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(© Corrine J. Humphrey/Index Stock)

C H A P T E R 9 C O N C E P T S

� Water is an essential macronutrient; to maintain fluid balance, intakemust equal losses.

� Sodium, chloride, and potassium are electrolytes. These and otherminerals are important in regulating blood pressure.

� Calcium, phosphorus, and magnesium are minerals needed for bonehealth.

� Iron is a component of the oxygen transport protein hemoglobin.Iron-deficiency anemia is the most common nutritional deficiencyworldwide.

� Copper functions in iron transport, connective tissue synthesis, lipidmetabolism, and antioxidant protection.

� Zinc is needed for many enzymes and for the activity of a number ofvitamins and hormones.

� Selenium is an essential part of the antioxidant enzyme glutathioneperoxidase.

� Iodine is essential for the synthesis of the thyroid hormones.� Chromium helps insulin function.� Fluoride is important for healthy teeth and bones.

Can taking a supplement of onemineral cause a deficiency of another?

How long can a person survive without water?

Does eating too much salt raise blood pressure?

Are iron supplements dangerous?

Ju s t A Ta s t e

Reuters Health

Study: OverweightChildren Risk IronDeficiencyTuesday, July 6, 2004—Overweight children are at doublethe risk of being iron deficient, perhaps because of baddiet or lack of exercise, a study said on Tuesday. . . .

Iron deficiency is a global problem most commonly foundin poorer people lacking proper nutrition, but the studyconcluded that the rising number of obese people in thedeveloped world should be checked and treated for it.

Too little iron in the blood can cause anemia and leadto learning and behavioral problems as well as poselimits on work and exercise.

One out of seven U.S. children is overweight, a three-foldincrease in the past 30 years, and many do not get screenedfor iron deficiency, Yale University researcher Karen Neadwrote in the journal Pediatrics.

To read the complete article, go to www.nlm.nih.gov/medlineplus/news/fullstory_18782.html.www.iconcast.com/H/HealthGuideB7.6/NewsonHealth3.htm

279

9Water and Minerals

Water and Minerals Make Up the Sea Within UsSome Minerals Are Needed in Large Amounts,

Some in Minute AmountsWe Consume Minerals from Both Plant and Animal

Sources

Water Is Essential to LifeOver Half of Your Body Weight Is WaterWater Requirements Depend on Water Losses

Sodium, Potassium, and ChlorideAre the ElectrolytesElectrolytes Are Essential for Nerve Conduction,

Muscle Contraction, and Fluid BalanceThe Modern Diet Is High in Sodium and Low

in Potassium

Hypertension Is High Blood PressureMineral Intake Can Affect the Risk of HypertensionThe Total Diet Is Important for a Healthy Blood Pressure

Calcium and Other Minerals AreNeeded for Healthy BonesBone Is a Living TissueOsteoporosis Increases the Risk of Bone FracturesCalcium Levels Are Carefully Regulated

Phosphorus Is Found in Bone and Almost Everywhere ElsePhosphorus Levels Are Regulated to Promote Bone

HealthIt Is Not Difficult to Get Enough Phosphorus in Your Diet

Magnesium Is Needed in Bone and Body FluidsIron Is Needed to Transport Oxygento Body TissuesIron Deficiency Causes Weakness and FatigueAbsorption Regulates How Much Iron Is in the BodyWomen Require More Iron than MenToo Much Iron Is Toxic

Copper Deficiency Can Cause IronDeficiency AnemiaZinc Is Needed for Enzyme,Hormone, and Vitamin ActivityA High Phytate Intake Can Cause Zinc DeficiencyToo Much Zinc Can Override Regulatory Mechanisms

Selenium Provides AntioxidantProtectionIodine is Needed to SynthesizeThyroid HormonesChromium Helps Regulate Blood SugarFluoride Prevents Cavities

INTRODUCTION

ow can someone be overweight and still sufferfrom a nutrient deficiency? In the United Statesand other developed countries, where diseases re-lated to overconsumption are the obvious prob-lem, we tend to forget about the dangers of

nutrient deficiencies. Many of the deficiencies that werepublic health problems in the early part of the 20th centuryhave been virtually eliminated by our plentiful and fortifiedfood supply, but poor food choices can still create nutrientdeficiencies even among those who are consuming morethan enough calories. Several of the nutrients at risk for defi-ciency in the American diet are minerals. As this article illus-trates, poor iron intake puts many at risk of iron deficiencyanemia and despite the fact that most Americans have plentyto eat, low intakes of calcium and zinc are also a concern.

H

280 Chapter 9 Water and Minerals

The complex molecules necessary for the emergence of life were forged in theearth’s first oceans. These primordial seas supported life because they were rich ininorganic minerals as well as organic substances. As organisms grew in complexity,the water and chemicals critical to their survival were incorporated into an internalsea. The right proportion of water and dissolved substances was necessary to allowall of the chemical reactions that sustain life. Today, our body fluids still haveabout the same composition as the oceans of primitive earth. Just as the right com-bination of water, organic molecules, and minerals was needed for the beginning oflife, the right combination is necessary in the body for the maintenance of life(Figure 9.1).

Some minerals are needed in large amounts,some in minute amountsThere are over 20 minerals that you need to include in your diet to stay healthy.Some of these make up a significant portion of your body weight, others are foundin only minute quantities. If more than 100 mg per day is required, an amountequivalent in weight to about 2 drops of water, the mineral is considered a majormineral; these include sodium, potassium, chloride, calcium, phosphorus, magne-sium, and sulfur. Minerals that are needed in smaller amounts are referred to astrace elements; these include iron, copper, zinc, selenium, iodine, chromium, fluo-ride, manganese, molybdenum, and more. Just because you need more of themajor minerals than the trace elements doesn’t mean that one group is more im-portant than the other. A deficiency of a trace element such as copper is just asdamaging to your health as a deficiency of one of the major minerals, such as cal-cium (Figure 9.2).

Minerals provide structure and regulate functionMinerals contribute to body structure and are involved in the regulation of theprocesses that maintain life. Many serve more than one function. For example, weneed calcium to keep our bones strong as well as to keep blood pressure normal, allowmuscles to contract, and transmit nerve signals from cell to cell. Some minerals help

Water and Minerals Make Up the Sea within Us

H

Li Be

Na

K Ca

Mg

Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga

Al

B

Si

C

P

N

S

O

Cl

F

Ar

Ne

He

Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra Ac Unq Unp Unh Uns Une

F I G U R E 9 . 1

The composition of the fluid inside our bodiesis similar to that of the oceans of primitiveearth where simple life forms such as thoseshown here first evolved. (Science Vu/ VisualsUnlimited)

F I G U R E 9 . 2

Minerals are chemical elements found in theperiodic table. The major minerals are shownin purple, and the trace elements are shownin blue.

Minerals Elements needed by thebody in small amounts for structure andto regulate chemical reactions and otherbody processes.

�*

Major minerals Minerals needed in thediet in amounts greater than 100 mg/per dayor present in the body in amounts greaterthan 0.01% of body weight.

�*

Trace elements Minerals required inthe diet in amounts of 100 mg or less perday or present in the body in amounts of0.01% of body weight or less.

�*

regulate fluid balance, others help regulate energy production, and some affect geneexpression. Many minerals act as cofactors needed for enzyme activity. None of theminerals we require act in isolation. Instead, they interact with each other as well asvitamins and other dietary components.

We consume minerals from both plant and animal sourcesFoods from both plants and animals provide good sources of minerals in our diet.Some of these minerals are present as functioning components of the plant or animaland are therefore present in consistent amounts. For instance, the iron content of meatis predictable because the iron is part of a protein in muscle that gives the meat its redcolor. In other foods, minerals are present as contaminants; where a food is grown andhow it is processed can affect its mineral content. For example, plants grown in an areawhere the soil is high in selenium are higher in selenium than plants grown in otherareas. The mineral content of some animal products may vary depending on the con-tent of the grasses on which the animals forage. Processing also affects the mineral con-tent of food, in some cases removing minerals and in others adding them. For example,when fruits and vegetables are peeled, the minerals in the skins are lost. When the branand germ of grains are separated the minerals they contain are removed from the grain.Enrichment adds the lost iron back to grain products and the fortification of breakfastcereals and other products adds calcium, iron, and other minerals. The mineral contentof the diet can be maximized by eating a variety of foods, including many unprocessedor less processed foods such as fresh fruits, vegetables, nuts, legumes, whole grains andcereals, milk, seafood, and lean meats (Figure 9.3).

Mineral absorption varies from food to food,meal to meal, and person to personThe bioavailability of the minerals that we consume in foods varies. For some miner-als, such as sodium, we absorb almost all of what we eat, but for others we only absorba small percentage; calcium absorption is typically about 25% and iron absorptionmay be as low as 5%. How much of a particular mineral is absorbed may vary fromfood to food, meal to meal, and person to person.

The food source of a mineral affects its absorption; in general the mineralsfound in animal products are better absorbed than those found in plant foods. Thedifference in absorption is due in part to the fact that plants contain substancesthat interfere with mineral absorption. For instance, phytates found in wholegrains, bran, and soy products bind calcium, zinc, iron, and magnesium, limitingtheir absorption. Tannins, found in tea and some grains, can interfere with iron ab-sorption, and oxalates, which are organic acids found in spinach, rhubarb, beetgreens, and chocolate, have been found to interfere with calcium and iron absorp-tion (Figure 9.4). Dietary fiber also interferes with mineral absorption. Althoughthe North American diet generally does not contain enough of any of these com-ponents to cause a trace element deficiency, diets in developing countries may. Forexample, in some populations the intake of phytates is high enough to cause a zincdeficiency.

The presence of one mineral can also interfere with the absorption of another.For example, mineral ions that carry the same charge compete for absorption inthe gastrointestinal tract. Calcium, magnesium, zinc, copper, and iron all carry a2� charge so, for example, a high intake of calcium may reduce the absorption ofiron. Although generally not a problem when whole foods are consumed, a largedose of one mineral from a supplement may interfere with the absorption of otherminerals.

The amount of a mineral already present in the body also affects how much is ab-sorbed. For instance if there is plenty of iron stored in your body, you will absorb lessof the iron you consume. Life stage can also affect absorption; calcium absorptionmay double during pregnancy.

Water and Minerals Make Up the Sea within Us 281

Cofactor An inorganic ion orcoenzyme required for enzyme activity.�*

F I G U R E 9 . 3

The mineral content of your diet can bemaximized by eating a variety of nutrient-dense foods. (© PhotoDisc)

F I G U R E 9 . 4

Compounds such as phytic acid, oxalates,and tannins found in these foods decreasemineral absorption. (Charles D. Winters)

Mineral supplements can helpprevent deficiencies, but theymay also contribute to them.Because minerals often competewith each other for absorption,consuming a supplementcontaining a large amount of asingle mineral can interfere withthe availability of other mineralsconsumed at the same time.

Men are more watery than women.A man’s body is 60 to 65% water,compared to 50 to 60% for a woman.This difference is because men havemore muscle, which contains a lot of water, and women have more fat,which has almost no water.


Water Is Essential to Life

Did you ever feel nauseous, light-headed, or dizzy while exercising on a hot day? If soyou might have been suffering from dehydration. Dehydration, a depletion of bodywater, will cause symptoms more rapidly than a deficiency of any other nutrient. Forexample, days and even weeks without some vitamins and minerals will not cause de-ficiency symptoms, but an hour of exercise on a hot day can result in dehydration(Figure 9.5).

Over half of your body weight is waterIn adults, about 60% of body weight is water. The percentage is higher in small chil-dren; infants have the highest percentage of water—about 70%. Body water decreasesin older adults. Water is found in varying proportions in all the tissues of the body;muscle is about 75% water and bone is about 25% water. Some water is found insidecells and is known as intracellular fluid and some, referred to as extracellular fluid, islocated outside cells. Extracellular fluid accounts for about a third of total body waterand is made up primarily of the water in blood and the fluid between cells, calledinterstitial fluid. Other extracellular fluids include lymph and fluids inside the lumenof the GI tract, the eyes, joints, and spinal cord.

Water moves in and out of body cellsThe water inside your bloodstream, cells, and the spaces between cells is not trappedthere. The cell membranes between these compartments are not watertight bags; watercan pass right through them. The water is held in cells and other body compartmentsby the proteins, sodium, potassium, and other small molecules that are dissolved inyour body water. Water moves back and forth between different body compartmentsin order to equalize the concentration of dissolved particles. When the concentrationof particles in one compartment is higher than in another, water will move toward thecompartment with the most dissolved substances. This diffusion of water is called os-mosis; water moves across membranes from an area with a lower particle concentra-tion to an area with a higher particle concentration (Figure 9.6). Osmosis occursthroughout nature. For example, if you sprinkle sugar on a fresh strawberry, the waterinside the strawberries will move across the skin of the strawberry to try to equalizethe sugar concentration on each side. In the body, the concentration of dissolved par-ticles affect where water is located. For example, if the concentration of sodium in the

Dehydration Excessive loss of waterresulting in depletion of body fluids.�*

Intracellular fluid The fluid locatedinside cells.�*

Extracellular fluid The fluid locatedoutside cells. It includes fluid found in theblood, lymph, gastrointestinal tract, spinalcolumn, eyes, joints, and that foundbetween cells and tissues.

�*

F I G U R E 9 . 5

Exercise in a hot environment can dramatically increase water lossesfrom sweat and lead to dehydration. (D. Clarke Evans/Getty ImagesNews and Sport Services)

Interstitial fluid The portion of theextracellular fluid located in the spacesbetween cells and tissues.

�*

Osmosis The passive movement ofwater across a membrane to equalize theconcentration of solutes on both sides.

�*

RememberOsmosis not only drives the movement of water from one body compartment toanother, but also allows water from the diet to move from the lumen of thegastrointestinal tract into the blood (see Chapter 3).

*

blood is higher than in the surrounding cells, water will be drawn into the blooddiluting the sodium. The body can regulate the amount of water in each compart-ment by adjusting the concentration of dissolved particles and relying on osmosis tomove the water.

The movement of water from one compartment to another also depends on fluidpressure. The fluid pressure of blood against the blood vessel walls, or blood pressure,causes water to be pushed out of the blood and into the spaces between cells. Whenthe pressure is lower, the water is drawn back into the blood by osmosis.

Water in the body provides many functionsWater bathes the cells of the body and lubricates and cleanses internal and externalbody surfaces. Watery tears lubricate the eyes and wash away dirt, synovial fluid lubri-cates the joints, and saliva lubricates the mouth, making it easier to chew and swallowfood. Water resists compression so it cushions body compartments such as the jointsand eyeballs against shock. The cushioning effect of water in the amniotic sac protectsthe fetus as it grows inside a pregnant woman. Blood, which is mostly water, flowsthrough our bodies, delivering oxygen and nutrients to cells and returning waste prod-ucts to the lungs and kidneys for excretion. In addition, water functions in chemicalreactions and helps regulate body temperature.

Water functions in chemical reactions Water is an excellent sol-vent; glucose, amino acids, minerals, and many other substances needed by bodycells dissolve in water. The chemical reactions of metabolism that support life takeplace in water. Water also participates directly in a number of chemical reactionsthat join small molecules together or break large molecules apart. Some of the reac-tions in which water participates help maintain the proper level of acidity in thebody.

Water helps regulate body temperature Water is important inmaintaining body temperature. The fact that water holds heat and changes tempera-ture slowly helps keep body temperature constant, but water is also more actively in-volved in temperature regulation.

The water in blood helps regulate body temperature by increasing or decreasingthe amount of heat lost at the surface of the body. When body temperature startsto rise, the blood vessels in the skin dilate, causing blood to flow close to the sur-face where it can release some of the heat to the surrounding air. The increasedblood flow at the surface is the reason your skin becomes red in hot weather orduring strenuous activity. In a cold environment the opposite occurs. The bloodvessels in the skin constrict, restricting the flow of blood near the surface and con-serving body heat.

Water also helps regulate body temperature through the evaporation of sweat.When body temperature increases, the brain triggers the sweat glands in the skin toproduce sweat, which is mostly water. As the sweat evaporates from the skin, heat islost, cooling the body.

Water Is Essential to Life 283

Cell swellsNet movement of

water in

Cell shrinksNet movement of

water out

No change incell shape

No net movementof water

Low salt outside High salt outsideSame salt in and out

F I G U R E 9 . 6

When the fluid surrounding a cell is lower in dissolved substances than the fluid withinthe cell, there is a net movement of water into the cell by osmosis (left panel). When theconcentration is equal there is no net movement of water (middle panel). When theextracellular fluid is higher in dissolved substances than the intracellular fluid, there is a net movement of water out by osmosis and the cell will shrink (right panel).

Body temperature is closelyregulated to maintain a normallevel of around 98.6�F. If the bodytemperature rises above 108�F orfalls below 80�F, death is likely.

Blood pressure The amount of forceexerted by the blood against the arterywalls.

�*


Water intake and water losses are regulatedBecause water is so important, our bodies have mechanisms that help to regulate theamount we consume and the amount we excrete. Most of our water intake is fromwater and other fluids that we drink. Solid foods also provide water; most fruits andvegetables are over 80% water and even roast beef is about 50% water. A smallamount of water is also produced in the body as a by-product of metabolic reactions.We lose water from our bodies in urine and feces, through evaporation from the lungsand skin, and in sweat. A typical young man loses close to 3 quarts of water daily. Be-cause water cannot be stored, to maintain the right amount of water in your bodywater intake and excretion must be balanced (Figure 9.7).

Feeling thirsty tells you to drink The need to consume water is sig-naled by the sensation of thirst. Thirst is caused by dryness in your mouth as well assignals from the brain. Your mouth becomes dry because less water is available tomake saliva. Thirst signals arise when the thirst center in the brain senses a decrease inthe amount of fluid and an increase in the concentration of dissolved substances inblood. Together, your dry mouth and signals from your brain make you feel thirstyand motivate you to drink.

Thirst is a powerful urge, but it cannot be relied on to regulate how much water isin the body. The sensation of thirst often lags behind the need for water and you don’tor can’t always drink when you are thirsty. Not drinking enough to replace losses canbe a problem for athletes exercising in hot weather. They lose water rapidly but do notfeel thirsty until they have lost so much body water that their performance has beencompromised.1 To maintain adequate fluid balance it is recommended that athletesdrink every few minutes whether or not they feel thirsty.

The kidneys regulate water lost in the urine Under most cir-cumstances, the majority of water losses occur in the urine. To ensure proper waterbalance, water loss in urine is regulated by the kidneys. The kidneys typically produceabout 1 to 2 liters (about a quarter to a half a gallon) of urine per day, but urine pro-duction varies depending on the amount of fluid consumed and the amount of wasteproducts that need to be excreted.

The kidneys function like a strainer. As blood flows through them, water and smallmolecules are filtered out and blood cells and large molecules are retained. Some ofthe water and molecules that pass through the filter are reabsorbed into the blood andthe rest are excreted in the urine. The amounts that are reabsorbed depend on condi-tions in the body. When the concentration of dissolved particles in the blood is high,as it would be in an athlete who has not consumed enough water, a hormone calledantidiuretic hormone (ADH) signals the kidneys to reabsorb water, reducing theamount lost in the urine. This reabsorbed water is returned to the blood, preventingthe concentration of dissolved particles from dropping further. When the particle con-centration in the blood is low, as it might be after drinking several glasses of water,

Drink1500ml

Urine1450ml

Food1000ml 1100ml

Evaporation

250ml

Metabolism

200ml

Feces

F I G U R E 9 . 7

To maintain water balance, intake must equal output. This figureapproximates the amounts of water from different sources that make upwater intake and the amounts and route of lost water in a 70-kg adult who isnot losing water in sweat.

Antidiuretic hormone (ADH) Ahormone secreted by the pituitary glandthat increases the amount of waterreabsorbed by the kidney and thereforeretained in the body.

�*

Alcohol inhibits the activity ofADH, increasing water loss. Someof the effects of a “hangover” fromconsuming too much alcohol aredue to dehydration.

ADH levels decrease so less water is reabsorbed and more is excreted in the urine, al-lowing blood solute concentration to increase to normal (Figure 9.8). The amount ofwater lost from the kidneys is also adjusted by regulating the amount of sodium andother particles dissolved in the blood.

Even though the kidneys work to control how much water is lost, this function hasits limits. In order to allow the kidneys to continue to work, there is a minimumamount of water that must be lost as wastes are excreted. If there are a lot of wastes tobe excreted, more water must be lost. Wastes that must be eliminated in the urine in-clude urea and other nitrogen-containing waste products from protein breakdown, ke-tones from fat breakdown, and phosphates, sulfates, electrolytes, and other minerals.

Other water losses are not regulated The amount of water lost infeces and sweat and through evaporation is not regulated. Under certain circum-stances these losses can be great enough to be a danger to health and life.

In a healthy person only a small amount of water is lost in the feces, usually lessthan a cup. This is remarkable because every day about 9 liters (a little over 2 gallons)of fluid enters the gastrointestinal tract. In a healthy person more than 95% of thisfluid is reabsorbed before the feces are eliminated. However, in cases of severe diarrhealarge amounts of water can be lost via this route. If the lost fluid is not replacedquickly, the individual may become severely dehydrated.

Although we are not aware of it, we are continuously losing water from the skin andrespiratory tract due to evaporation. Amounts of water lost through evaporation varygreatly depending on activity, temperature, humidity, and body size. An inactive personat a moderate temperature loses about a liter per day; the amount increases with activ-ity, environmental temperature, and body size and decreases in high humidity. For ex-ample, more water will evaporate from your skin and lungs when you are walking inthe desert than when you are window shopping on a rainy day. Water is also lostthrough sweat when you exercise or when the temperature gets too hot. More sweat isproduced as exercise intensity increases and as the environment becomes hotter andmore humid. An individual doing light work at a temperature of about 84�F will loseabout 2 to 3 liters of sweat per day. Strenuous exercise in a hot environment can causewater losses in sweat to be as high as 2 to 4 liters in an hour.2 Clothing that allows theevaporation of sweat will permit the body to be cooled and will decrease sweat losses.

Water requirements depend on water lossesWater cannot be stored in the body and it is continuously lost, mostly through evapo-ration and urinary losses, so a steady supply must be consumed. Gram for gram, weneed more water each day than any other nutrient. The DRIs recommend 3.7 liters(3700 grams) per day for men and 2.7 liters (2700 grams) per day for women.3 How-ever, the amount you actually need is affected by your diet and activity level as well asenvironmental temperature and humidity. Activity increases water needs because it in-creases the amount of water lost in sweat; losses are greater in hot and humid environ-ments. The composition and adequacy of the diet also affect water needs. Alow-calorie diet increases water needs because as body fat and protein are brokendown to fuel the body, ketones and urea are produced and must be excreted in theurine. A high-sodium diet increases water losses because the excess salt must be ex-creted in the urine. A high-fiber diet increases water needs because more water is heldin the intestines and excreted in the feces.

Dehydration can be life-threatening Even small changes in theamount of water in the body can be life-threatening. Without food, you could proba-bly survive for about 8 weeks, but without water, you would last only a few days. Whenwater losses are great enough to reduce blood volume, the ability to deliver oxygen andnutrients to cells and remove waste products is affected. Early symptoms of dehydra-tion include thirst, headache, fatigue, loss of appetite, dry eyes and mouth, and dark-colored urine. Further loss affects thinking ability and physical performance. Latersymptoms include nausea, difficulty concentrating, confusion, and disorientation.

Water is Essential to Life 285

Kidneys

Release ofantidiuretic hormone

DECREASE INBODY WATER

LESS WATER LOSTIN URINE

F I G U R E 9 . 8

When an individual hasn’t consumed enoughfluid or loses too much water, the volume ofbody water decreases, signaling the pituitarygland to secrete antidiuretic hormone. Thishormone acts on the kidneys to increasewater reabsorption, thereby decreasing waterlosses in the urine.

Every year about 4 billion cases ofdiarrhea occur, causing 2.2 milliondeaths, mostly among children underthe age of 5.This is equivalent to 1 child dying every 15 seconds.Thesediarrhea-related deaths representapproximately 15% of all child deathsunder the age of 5 in developingcountries.The diarrhea is usuallycaused by a microbial infection, butthe death is caused by dehydration.

Infants need proportionately morewater per calorie than adultsbecause they lose more water intheir urine and through evaporation.


Dehydration is more likely to occur during exercise because water loss through sweatis increased. Drinking at regular intervals while you exercise to replace the water youare losing can prevent dehydration. Its mild symptoms disappear quickly after con-suming fluids, but if left untreated it can require medical attention. A loss of about 10to 20% of body weight as water can be fatal.

Young athletes involved in sports with weight classes, such as wrestling and boxing,sometimes use dehydration to reduce their body weight so they can compete in a lowerweight class. Being at the high end of the lower weight class is thought to provide an ad-

Your Choice: Is Bottled Water Better?

A bottle of water can cost anywhere from 69 cents in aminimart to $5 in a posh restaurant. For the price of onebottle of Evian, you could use 1000 gallons of water fromyour tap at home. Nonetheless, bottled water is an $8billion industry in the United States; Americans drank 5billion gallons in 2001.1 Why are we willing to pay so muchfor that glass of water? Is bottled better?

We buy bottled water assuming that the bottle is aguarantee of purity, but in reality, the jug at the watercooler and the Dasani that you guzzle at the gym may notbe any safer than tap water. The standards for the purity forbottled water are comparable to the minimum standards setby the Environmental Protection Agency (EPA) for municipalwater systems.2 Because the standards that regulate bottledwater are no more rigid than those regulating tap water, itis not surprising that some bottled water actually is tapwater. By definition, bottled water doesn’t have to beanything special; it can be any water as long as it has noadded ingredients except safe and suitable antimicrobialagents. In fact about 25% of the bottled water sold in theUnited States is from municipal water supplies.

To help consumers identify the source of their bottledwater and make labeling consistent from state to state, theFDA established standard definitions for all bottled water

products.3 Under these regulations, bottled water thatcomes from tap water must be clearly labeled as such.However, water that has been taken from a municipal watersupply and then treated—for example, filtered ordisinfected—need not indicate that it is tap water. “Distilledwater” and “purified water,” are examples of water takenfrom municipal water supplies and then treated. If you wantwater that did not come from the tap, select artesian water,spring water, well water, or mineral water. These come fromunderground water sources. Be aware however of wordslike “pure”, “pristine”, and “glacial”. They are added toemphasize the alleged purity of bottled water compared totap, but they have no set definitions or meanings.

When choosing your water, weigh the benefits against therisks. Bottled water is more expensive, and whether you aredrinking tap water or buying bottled water off the shelf,contamination is possible. A study by the National ResourcesDefense Council tested 1000 bottles of 103 different brands ofbottled water and found that although the quality of mostsamples was good, it was not necessarily purer or safer thantap water.2 The safest alternative is to buy distilled water. Inthe distillation process, nonvolatile chemicals are removed,and the heat destroys bacteria and other biologicalcontaminants. The resulting water is probably free ofcontaminants, but it is tasteless and lacking in essential dietaryminerals that water usually supplies. Before making a choice,take a look at the results of water-monitoring tests your watercompany is required to perform and compare them with thelegal limits of contaminants set by the EPA. This should helpyou decide. For more information, contact the FDA(www.fda.gov), the International Bottled Water Association(www.bottledwater.org), or the EPA (www.epa.gov).

References1. FDA Consumer Magazine. Bottled water: Better than tap? July–August 2002.

Available online at www.fda.gov/fdac/features/2002/402_h2o.html/AccessedAugust 20, 2004.

2. Safe drinking water: www.epa.gov/safewater/crypto.html/Accessed August 20,2004.

3. National Resources Defense Council. Clean water & oceans: Drinking water.Bottled Water: Pure Drink or Pure Hype? Executive Summary. Available onlineat www.nrdc.org/water/drinking/bw/exesum.asp/Accessed August 20, 2004.(Larry Williams/Corbis Images)

vantage over smaller opponents in that class.4 However, when weight loss is accomplishedthrough even mild dehydration, exercise performance can be impaired (see Chapter 11).

Consuming too much water dilutes the internal sea It is diffi-cult to consume too much water under normal circumstances. However, overhydrationmay occur with illness or, in certain situations, during exercise. For example, water andminerals are lost in sweat. When these losses are replaced with plain water the balance ofwater and dissolved substances is disrupted. Drinking plain water after excessive sweating islike pouring out half a glass of salt water and refilling the glass with plain water. The totalamount of water is the same but the salt in the glass is now more dilute. The same thingcan happen to your blood and is referred to as water toxicity. The early symptoms of watertoxicity may be similar to dehydration: nausea, muscle cramps, disorientation, slurredspeech, and confusion. It is important to determine if the symptoms are due to dehydra-tion or water toxicity because drinking water alone will make toxicity worse and can resultin seizure, coma, or death. To help prevent water toxicity it is recommended that beveragescontaining dilute solutions of sodium as well as sugar, such as sports beverages, be used toreplace water losses when exercise continues for more than an hour (see Chapter 11).

Sodium, Potassium, and Chloride Are the Electrolytes 287

Sodium, Potassium, and Chloride Are the Electrolytes

Keeping your body alive and moving requires the transmission of nerve impulses andthe contraction of muscles. These activities are triggered by the movement of electri-cally charged ions dissolved in water. These ions conduct an electrical current and aretherefore referred to as electrolytes. Sodium, potassium, and chloride are key elec-trolytes in your body. Electrolytes also help regulate fluid balance and are importantfor maintaining acid-base balance throughout the body (Table 9.1).

Electrolytes are essential for nerve conductionand muscle contractionEvery thought, every movement, and every response you make requires that a nerve im-pulse speed through your body to a target cell. Nerve impulses are created by the move-ment of sodium and potassium ions across the nerve cell membrane. Sodium andpotassium are both positively charged ions; sodium is concentrated outside cells,whereas potassium is concentrated inside cells where it is 30 times more concentratedthan outside the cell. The imbalance of sodium and potassium as well as a greater con-centration of positive ions just outside the cell membrane are forces that attract sodiumto the inside of cells. When a nerve cell is at rest sodium stays outside the cell becausesodium ions cannot pass freely across cell membranes. But, when a nerve is stimulated,the cell membrane becomes more permeable to sodium, allowing sodium ions to rushinto the nerve cell. When this happens, the positive charge inside the cell increases caus-ing the electrical charge at that location on the cell membrane to be reversed; this trig-gers an increase in sodium permeability on the adjacent patch of membrane. The changein sodium permeability and electrical charge continues to spread down the nerve as anerve impulse. If the nerve signal travels to a muscle cell, similar events occur at themuscle cell membranes and result in muscle contraction. Once the nerve impulse passes,the original resting concentrations of sodium and potassium inside and outside themembrane are restored so a new nerve signal can be triggered if the nerve is stimulated.

Balancing electrolytes helps balance body fluidsDid you ever weigh yourself after eating a very salty meal to find that you had gained afew pounds? The salt, which is sodium combined with chloride, was absorbed intoyour blood increasing the sodium concentration. This imbalance made you thirstyand stimulated you to drink enough to dilute the sodium in your blood. The extra

Ion An atom or group of atoms thatcarries an electrical charge.�*

Electrolytes Substances thatseparate in water to form positively andnegatively charged ions that conduct anelectrical current. In nutrition this termrefers to sodium, potassium, and chloride.

�*

If you are stranded on a desertisland, your first priority iswater. You can survive for weekswithout any food, but a lack ofwater can be fatal in a matterof days.


pounds you see on the scale reflect the extra water you have temporarily stowed away.By the next day your body will have had time to excrete the extra sodium and thewater along with it in your urine, bringing your weight back to normal.

Electrolyte levels are carefully regulated Our bodies are efficientat regulating the internal concentrations of electrolytes, even when dietary intake variesdramatically. For example, in northern Japan, sodium intake is greater than 10.3 gramsper day and among the Yanomamo Indians of Brazil, it is less than 0.2 grams per day,yet, blood levels of sodium are not significantly different among these groups.3

T A B L E 9 . 1A Quick Summary of the Major Minerals

Recommended Groups atFood Intake Major Deficiency Risk of Toxicity

Mineral Sources for Adults Functions Symptoms Deficiency and UL

Sodium Table salt, 1500 mg/day Major positive Muscle Those consuming Contributesprocessed extracellular ion, cramps a severely sodium to high bloodfoods nerve transmission, restricted diet, pressure in salt

muscle contraction, sweating sensitivefluid balance excessively people; UL is

2300 mg

Potassium Fresh 4700 mg/day Major positive Irregular Those consuming Abnormalfruits and intracellular ion, heartbeat, poor diets high heartbeat; novegetables, nerve transmission, fatigue, in processed ULlegumes, muscle contraction, muscle foods, thosewhole fluid balance cramps taking thiazidegrains, milk, diureticsand meat

Chloride Table salt, 2300 mg/day Major negative Unlikely None None likely;processed extracellular UL is 3600 mgfoods ion, fluid balance

Calcium Dairy 1000–1200 Bone and tooth Increased Postmenopausal Kidney stonesproducts, fish mg/day structure, nerve risk of women, elderly, in susceptibleconsumed transmission, osteoporosis those with individuals;with bones, muscle contraction, kidney disease UL is 2500 mgleafy green blood clotting, from food andvegetables, blood pressure supplementsfortified regulation, hormonefoods secretion

Phosphorus Meat, dairy, 700 mg/day Structure of bones Bone loss, Premature Calciumcereals, and and teeth, weakness, infants, resorptionbaked goods membranes, ATP, lack of alcoholics, from bone;

and DNA; acid-base appetite elderly UL is 4000 mgbalance

Magnesium Greens, 310–420 mg/day Bone structure, Nausea, Alcoholics, Nausea,whole grains, ATP stability, enzyme vomiting, those with vomiting, low nuts, seeds activity, nerve and weakness, kidney and blood pressure;

muscle function muscle gastrointestinal UL is 350 mgpain, heart disease from nonfoodchanges sources

Sulfur Protein foods, None specified Part of the structure None when None None likely;preservatives of some amino protein needs no UL

acids and vitamins are met

When we get thirsty, it means we need water. When we feel like a salty snack, doesthis mean we need salt? Most likely that answer is no. When salt intake is very low,there is a salt appetite, which causes you to crave salt, but most of us eat far too muchsalt for this appetite to be activated. The salt cravings that trigger your desire to plungeinto a bag of salty chips is a learned preference, not a physiological drive for salt (Fig-ure 9.9). If you cut back on your salt intake you will find your taste buds becomemore sensitive to the presence of salt.

Although thirst and salt cravings may cause you to consume more water and salt,the kidneys, not intake, are the primary regulator of sodium, chloride, and potassiumbalance in the body. Excretion of these electrolytes in the urine is decreased when in-take is low and increased when intake is high. The regulation of blood levels of potas-sium is important because even a small increase can be dangerous. If blood levelsbegin to rise, body cells are stimulated to take up potassium. This short-term regula-tion prevents the amount of potassium in the extracellular fluid from getting lethallyhigh. The long-term regulation of potassium balance depends on the release of pro-teins that cause the kidney to excrete potassium and retain sodium.

Controlling sodium excretion helps regulate bloodpressure Because water follows sodium by osmosis, the ability of the kidneys toconserve sodium provides a mechanism to conserve body water. This mechanismhelps to regulate blood pressure. For example, if you are out exercising on a hot dayyou will lose water and salt in sweat. If you lose more than you take in it will cause adrop in blood volume, which causes a decrease in blood pressure. The body has sen-sors that detect changes in blood pressure. The drop in blood pressure triggers theproduction and release of proteins and hormones that affect the amount of sodium,and hence water, retained by the kidneys. The first substance to be released whenblood pressure decreases is the enzyme renin. It is produced by the kidneys and beginsa series of events leading to the production of a small protein called angiotensin II. An-giotensin II increases blood pressure in two ways. First, it causes the muscles in bloodvessel walls to constrict. This increases blood pressure by narrowing the lumen of theblood vessel. Angiotensin II also stimulates the release of the hormone aldosterone,which causes the kidneys to increase sodium reabsorption. As more sodium is reab-sorbed, water follows, preventing water loss and maintaining blood volume and, con-sequently, blood pressure (Figure 9.10). If blood pressure begins to rise, as mightoccur if you eat a salty meal, the increase in blood pressure inhibits the release of reninand aldosterone, relaxing blood vessels and increasing the excretion of sodium andhence water by the kidneys and decreasing blood pressure to normal.

Sodium, Potassium, and Chloride Are the Electrolytes 289

F I G U R E 9 . 9

Our taste for salty chips is a learnedpreference, not an indication that we need more salt. (© PhotoDisc)

Kidneys

LOW BLOOD PRESSURE

Renin helps formangiotensin II

NORMAL BLOOD PRESSURE

Release of aldosterone

Blood vesselsconstrict

Kidneys retain sodiumand water

F I G U R E 9 . 1 0

When blood pressure decreases, a series of events returnsblood pressure to normal by constricting blood vesselsand increasing sodium and water retention by the kidney.

Renin An enzyme produced by thekidney that aids in the conversion ofangiotensin to its active form, angiotensin II.

�*

Angiotensin II A compound that causesblood vessel walls to constrict and stimulatesthe release of the hormone aldosterone.

�*

Aldosterone A hormone that increasessodium reabsorption and therefore enhanceswater retention by the kidney.

�*

The typical American diet containsabout 8 grams of salt. Salt is 40%sodium and 60% chloride by weight,so 8 grams contains 3.2 grams ofsodium (8 � 40% � 3.2 g) and4.8 grams of chloride.


The modern diet is high in sodium and low in potassiumOur diet today is high in salt (sodium chloride) and low in potassium. The reason forthis is that we eat a lot of processed foods, which are high in sodium and chloride, andtoo few fresh unprocessed foods such as fruits, vegetables, whole grains, and freshmeats, which are high in potassium.

About 77% of the salt we eat is from that added during processing and manufac-turing (Figure 9.11). Only about 12% comes from salt found naturally in food, while11% is from salt added in cooking and at the table.3 Some of the sodium in processedfoods is from salt added for flavoring; potato chips, lunchmeats, and canned soups areall high in sodium chloride. Some of the sodium is added as a preservative. Salt in-hibits bacterial growth; we find it in our food as sodium chloride as well as othersodium salts, such as sodium bicarbonate, sodium citrate, and sodium glutamate. Lessthan 1% of the salt we consume is from tap water.3 Softened water or mineral water isoften higher in sodium than tap water and, if consumed in large quantities, can con-tribute significantly to daily sodium intake.

The human diet was not always high in salt. Prehistoric diets consisted of plantfoods such as nuts, berries, roots, and greens and fresh animal foods such as meat andmilk, which are high in potassium and low in salt. Because of its value as a foodpreservative and flavor enhancer salt was highly prized by ancient cultures in Asia,Africa, and Europe, where it was used in rituals as well as in the preservation of food.Roman soldiers were paid in sal, the Latin word for salt from which we get our wordsalary. Today, rather than a prized commodity, salt is a substance we attempt to limitin the diet. The reason for restricting salt is that diets high in salt have been implicatedas a risk factor for high blood pressure.

400 400

Potassium

Sodium

Peanuts, roasted(1 c)

Kidney beans, dry, cooked (1 c)

Pork, roasted(3 oz)

Chicken breast(3 oz)

1% milk(1 c)

Potato, baked(1 medium)

Green beans,fresh (1 c)

Tomato(1 medium)

Oatmeal(1 c)

Peanut butter(2 Tbsp)

Kidney beans,canned (1 c)

Ham, roasted(3 oz)

Chicken nuggets(3 oz)

Americancheese (1.5 oz)

French fries(20 pieces)

Green beans,canned (1 c)

Spaghetti sauce(1/2 c)

Cheerios(1 c)

Less processed More processed

0 800 0 800mg mg

F I G U R E 9 . 1 1

Less processed foods tend to be low in sodium and good sources of potassium. More processed foods are generally higher in sodium and may also be lower in potassium.

The DRIs recommend less salt and more potassium Mostpeople in the United States and Canada need to reduce their salt intake and increasetheir potassium intake to meet recommendations for a healthy diet. The recom-mended salt intake is 3.8 grams per day; this represents 1500 mg of sodium and2300 mg of chloride for adults ages 19 to 50 years. The Daily Value for sodium usedon food labels is no more than 2400 mg of sodium per day (6 grams salt). All ofthese values are significantly lower than the typical daily intake of between 6 and 12grams of salt.

The DRIs recommend an intake of potassium of 4.7 grams per day; the DailyValue is at least 3.5 grams per day for adults. This amount is a significant increaseabove the typical 2 to 3 grams consumed by most Americans. However, those whoconsume a diet high in fruits and vegetables will easily meet the potassium recommen-dation; daily intakes of 8000 to 11,000 mg are not uncommon.3

Electrolyte deficiency can occur when losses are in-creased The electrolytes are found in plentiful amounts in the diet, and the kidneysof a healthy individual are efficient at regulating amounts in the body. Deficiencies andexcesses can occur due to illness or extreme conditions. For instance, sodium, chloride,and potassium depletion can occur with heavy and persistent sweating, chronic diar-rhea or vomiting, and kidney disorders that lead to excessive excretion. Medicationscan also interfere with electrolyte balance. For example the diuretic medications,known as thiazide diuretics, that are used to treat hypertension cause potassium loss.Generally, potassium supplements are prescribed along with or incorporated into med-ications that cause potassium loss. Deficiencies of any of the electrolytes can lead toelectrolyte imbalance, which can cause disturbances in acid-base balance, poor appetite,muscle cramps, confusion, apathy, constipation, and, eventually, an irregular heartbeat.For example, the sudden death that can occur in fasting, anorexia nervosa, or starvationmay be due to heart failure caused by potassium deficiency.

Too much potassium can be deadly No UL has been set for potas-sium because consuming too much potassium from foods is not a risk in healthypeople with normal kidney function. If, however, supplements are consumed in ex-cess or kidney function is compromised, blood levels of potassium can increase andcan potentially cause death due to an irregular heartbeat. A high oral dose generallycauses vomiting, but if too much potassium enters the blood, it can cause the heartto stop.

Too much salt can contribute to high blood pressure If youeat more salt than you need, your kidneys will excrete the extra. However, in manypeople, the mechanisms that regulate blood pressure are unable to prevent rises inblood pressure as salt intake increases. These individuals are referred to as salt-sensitive. Based on the relationship between blood pressure and salt intake a ULhas been set at 5.8 grams of salt per day. For those without salt-sensitivity, no toxiclevel of sodium intake has been documented as long as water needs are met and thekidneys are functioning properly. Another concern with high-sodium intakes in-volves the mineral calcium. A high-sodium intake increases calcium excretion, thusincreasing the risk of bone loss.

Hypertension Is High Blood Pressure 291

On average, blood pressure riseswith increases in sodiumintake, but this response isvariable depending on theindividual. People with highblood pressure or diabetes,older adults, and AfricanAmericans tend to be moresensitive to the blood pressureraising effect of dietary salt.

Hypertension Blood pressure that is consistently elevated to 140/90 mm of mercury or greater.

�*

Hypertension Is High Blood Pressure

A healthy blood pressure is less than 120/80 mm of mercury. Blood pressure between120/80 and 139/89 is referred to as prehypertension and blood pressure that is consis-tently above 140/90 mm of mercury or greater is called hypertension (see AppendixC).5 Hypertension is caused by an increase in blood volume or a narrowing of theblood vessels. Elevated blood pressure is associated with increased risk of cardiovascu-


lar diseases such as atherosclerosis, heart attack, and stroke. It also increases the risksfor kidney disease and early death. It is estimated that 25% of adult Americans andmore than half of those over 60 years of age have blood pressure in this range (Figure9.12).3

Some of the risk of developing hypertensionis inheritedHypertension is a complex disorder, most likely resulting from disturbances in one ormore of the mechanisms that control body fluid and electrolyte balance. It often goesunnoticed because it rarely has recognizable symptoms. But, it can cause serious dam-age to the kidneys, heart, and blood vessels.

The risk of developing hypertension increases with a family history of the disease.It is more common in African Americans, Puerto Ricans, and Cuban and MexicanAmericans than in non-Hispanic whites. The increased incidence among AfricanAmericans is reflected in their 80% higher rate of death from stroke, 50% higher rateof death from heart disease, and 320% greater rate of hypertension-related kidney fail-ure compared to Caucasians.6

Whether you have a family member with hypertension or not, your risk of devel-oping high blood pressure increases as you get older and is higher if you are over-weight, particularly if your excess fat is in your abdominal region. A lack of physicalactivity, heavy alcohol consumption, and stress can also increase blood pressure.6 Reg-ular exercise can prevent or delay the onset of hypertension and weight loss can helpin obese individuals. Your risk of developing high blood pressure can also be increasedor decreased by your dietary choices.

Mineral intake can affect the risk of hypertensionYour intake of sodium, chloride, potassium, calcium, and magnesium can affect yourblood pressure and your risk of hypertension. Other dietary components such as theamount of fiber and the type and amount of dietary fat may also affect your risk of de-veloping high blood pressure. A dietary pattern that incorporates all of the recom-mended amounts of each of these can have a significant impact on blood pressure.7

Diets high in salt may increase blood pressure Diets high insalt are associated with a higher incidence of hypertension. This relationship was de-termined by looking at salt intake and blood pressure in different populations. It wasfound that populations with higher sodium intakes have higher blood pressure. Be-cause of this association, a reduction of sodium intake to 1500 mg per day is recom-mended to keep blood pressure in the healthy range. This level of sodium intake mayalso help prevent bone loss.3

Diets high in potassium, calcium, and magnesiumlower the risk of hypertension Populations that eat a diet high inpotassium, calcium, and magnesium have lower average blood pressure than thosewith lower intakes. However, because diets that are high in potassium are usuallyalso low in sodium, it is difficult to tell if the lower incidence of hypertension isdue to the high potassium or the low sodium. Potassium supplements have beenshown to decrease blood pressure but since excessive potassium intakes can causean irregular heartbeat, potassium supplements are not recommended unless super-vised by a physician. Increasing consumption of potassium-rich foods such as ba-nanas, oranges, and potatoes is a safer way to increase potassium intake. Calciumand magnesium supplementation has been shown to lower blood pressure slightly

F I G U R E 9 . 1 2

Hypertension has been called the silent killerbecause it has no outward symptoms but canlead to atherosclerosis, heart attack, stroke,kidney disease, and early death. Everyoneshould have their blood pressure monitoredregularly. (Charles D. Winters)

Water softeners remove someminerals, mainly calcium andmagnesium, from water and replacethem with sodium. Softened waterhas about twice the amount ofsodium as unsoftened water—about94 mg per liter. If you are followinga sodium-restricted diet, you mayneed to bypass the water softenerwhen it comes to drinking water.

For more information onthe incidence, causes,and treatment of highblood pressure, go to

the National Heart, Lung,and Blood Institute at

www.nhlbi.nih.gov/siteindex

in individuals with hypertension, and perhaps in those with normal blood pressure(Table 9.2).8,9

The total diet is important for a healthy blood pressureHigh blood pressure is a serious public health problem in the United States. The riskof developing it can be reduced by regular exercise, keeping your weight in the healthyrange, and following the recommendations of the DASH diet and other nutritionalguidelines.

DASH, which stands for Dietary Approaches to Stop Hypertension, is a dietarypattern that does just that. It recommends lots of fruits and vegetables, nine to ten aday! It also includes low-fat dairy products, whole grains and nuts, and a moderateamount of lean meats (Table 9.3). These foods provide moderate amounts of sodiumand lots of fiber, potassium, magnesium, and calcium; they are also low in total fat,saturated fat, and cholesterol. Reductions in blood pressure are even greater when theDASH diet pattern is combined with a reduction in sodium intake.10 Following aDASH dietary pattern can have as great an impact on blood pressure as medications.


T A B L E 9 . 2Keeping Blood Pressure in a Healthy Range

• Choose and prepare foods with less salt.• Aim for a healthy weight—blood pressure increases with increases in body

weight and decreases when excess weight is lost.• Increase physical activity—it helps lower blood pressure, reduce risk of other

chronic diseases, and manage weight.• Eat fruits and vegetables—they are naturally low in salt and calories. They are

also rich in potassium, which may help decrease blood pressure.• If you drink alcoholic beverages, do so in moderation. Excessive alcohol

consumption has been associated with high blood pressure.

Source: USDA, DHHS. Dietary Guidelines for Americans, 2000.

For more information on the DASH diet,go to the DASH diet site at the

National Heart, Lung,and Blood Institute at

www.nhlbi.nih.gov/health/public/heart

T A B L E 9 . 3DASHing Your Diet

Your Calorie Needs 1600 2000 2600 3100

Food Group Recommended Number of Servings*

Grains 6–7 7–8 10–11 12–13

Vegetables 3–4 4–5 5–6 6–7

Fruits 3–4 4–5 5–6 6–7

Low-fat dairy 2–3 2–3 3–4 3–4

Meats, fish, poultry 1–2 1–2 2 2–3

Beans, nuts, and seeds 1/3 1/2 2/3 3/4

Limit fats and sweets

*Serving sizes correspond to the serving sizes recommended by the Food GuidePyramid.


50% Less Sodium than our

regular spaghetti sauce(See side panel for

nutrition information.)

Net Wt. 16 oz. (450g)

Nutrition FactsServing Size 1/2 cup (125g)Servings Per Container about 3 /1 2

10%

2%0%0%

%Daily Value**

50 Calories from Fat 10Amount Per Serving

Calories

15%3%4%

Vitamin A 10% • Vitamin C 25%Calcium 2% • Iron 10%*Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.

2,500Calories: 2,000

Sat FatCholesterol

Less thanLess than

20g 25g

3,500mg375g

2,400mg300mg

2,400mg3,500mg300g25g

Total Fat Less than 65g

300mg

80g

SodiumPotassiumTotal Carbohydrate Dietary Fiber

Less than

30g

Light Spaghetti Sauce, 250 milligrams(mg) per servingRegular Spaghetti Sauce, 500mg perserving

Total Fat 1g Saturated Fat 0gCholesterol 0mgSodium 250mgPotassium 530mgTotal Carbohydrate 9g

Dietary Fiber 1g Sugars 7gProtein 2g

F I G U R E 9 . 1 3

Food labels help you determine how muchsodium a food contributes to the diet.

The DASH diet is a dietary pattern that may provide more health benefits thanjust lowering blood pressure. It is not that different from what other recommenda-tions are advising us to eat. The Dietary Guidelines encourages the consumption offresh fruits, vegetables, grains, meats, and dairy products. Following the Food GuidePyramid recommendations also results in a diet similar to DASH, particularly if youaim for the high end of the recommended servings of vegetables, fruits, dairy prod-ucts, and grains and frequently choose dry beans and nuts from the Meat, Poultry,Fish, Dry Beans, Eggs, & Nuts Group (see Table 9.3).

Recommendations for a healthy diet suggest a reduction in sodium consumption.You can lower your salt intake by limiting the use of salt added in cooking and at thetable as well as that consumed in processed foods. Food labels can help identify low-sodium foods. All the sodium-containing additives are itemized in the ingredient list,and the total sodium content per serving is included in the Nutrition Facts section.Food labels also list the sodium content of a serving as a percent of the Daily Value.The Nutrition Facts on the label shown in Figure 9.13 tell us that a serving ofspaghetti sauce contains 250 mg, or 10% of the Daily Value for sodium. Additionalinformation can be obtained from descriptors relating to the salt or sodium content ofa product (Table 9.4). Some medications can also contribute a significant amount ofsodium to your diet. Drug facts labels on over-the-counter medications can help iden-tify those that contain large amounts of sodium.


T A B L E 9 . 4Looking for Low Sodium Food

What the Label Says What It Means

Sodium-free Contains less than 5 mg of sodium per serving.

Salt-free Must meet criterion for “sodium-free.”

Very low sodium Contains 35 mg or less of sodium per serving.

Low sodium Contains 140 mg or less of sodium per serving.

Reduced or less sodium Contains at least 25% less sodium per servingthan a reference food.

Light in sodium Contains at least 50% less sodium per servingthan the average reference amount for samefood with no sodium reduction.

No salt added, without No salt added during processing, and the food added salt, and unsalted it resembles and for which it substitutes is

normally processed with salt. (If the food is not“sodium-free,” the statement “not a sodium-free food” or “not for control of sodium in thediet” must appear on the same panel as theNutrition Facts panel.)

Lightly salted Contains at least 50% less sodium per servingthan a reference amount. (If the food is not“low in sodium,” the statement “not a low-sodium food” must appear on the same panelas the “Nutrition Facts” panel.)

So, What Should I Eat?

To stay hydrated• Drink before, during, and after you exercise• Drink two extra glasses of water on hot days• Bring a bottle of water with you on the airplane• Keep a water bottle in your car

To reduce your salt intake• Choose unprocessed foods—they have less sodium than processed foods• Do not add salt to the water when cooking rice, pasta, and cereals• Flavor foods with lemon juice, onions, garlic, pepper, curry, dill, basil, oregano, or thyme rather than salt• Limit salty snacks like potato chips, salted nuts, salted popcorn, and crackers• Substitute sliced roasted turkey, chicken, or beef for bologna, corned beef, hot dogs, and smoked turkey• Watch the sauces—Worcestershire sauce, soy sauce, barbecue sauce, ketchup, and mustard add a lot

of salt

To boost your potassium intake• Double your vegetable serving at dinner• Take two pieces of fruit for lunch• Have orange juice instead of soda or punch


Calcium and Other Minerals Are Needed for Healthy Bones

Sticks and stones can break your bones. The familiar rhyme reminds you that yourbones are not as hard as rock. The reason is that bones, unlike rocks, have a proteinmatrix as well as hard mineral crystals (Figure 9.14). Calcium and phosphorus are themost abundant minerals in bones but magnesium, fluoride, and other trace elementsare also important for bone structure. Healthy bones also depend on adequate dietaryprotein and vitamin C to form and maintain collagen, the most abundant protein inthe bone matrix. Adequate vitamin D is needed to allow calcium absorption so appro-priate levels of calcium and phosphorus are present in the blood.

Bone is a living tissueLike other tissues in the body bone is alive and is constantly being broken down andre-formed throughout life. Most bone is formed early in life. In the growing bones ofchildren, bone formation occurs more rapidly than breakdown so the total amount ofbone increases. Even after growth stops, bone mass continues to increase into youngadulthood. The greatest amount of bone that you have in your lifetime is called peakbone mass; peak bone mass is achieved somewhere between the ages of 16 and 30.After about age 35 to 45, the amount of bone broken down begins to exceed thatwhich is formed, so total bone mass decreases. Over time, if enough bone is lost, theskeleton is weakened and fractures occur more easily.

Osteoporosis increases the risk of bone fracturesOsteoporosis is a loss of bone that is great enough to increase the risk of bone fractures.You can’t feel your bones weakening so people with osteoporosis may not know theirbone mass is dangerously low until they are in their 50’s or 60’s and experience a bonefracture. Osteoporosis is caused by a loss of both the protein matrix of bone and theminerals that are embedded in it (Figure 9.15). In the United States, about 28 millionpeople have osteoporosis or are at risk due to low bone mass, and 80% of them arewomen.11,12 Osteoporosis leads to 1.5 million fractures annually, which account for $10to $15 billion per year in medical costs.11 Your risk of osteoporosis is affected by howdense your bones are, that is, your bone mass, and how fast you lose bone. The greater aperson’s bone mass and the slower bone is lost, the lower the risk of osteoporosis.

Peak bone mass is determined by genetics, gender, andlifestyle Someone who has more bone to begin with can lose more bone before beingat risk for fractures. How dense your bones are is determined by your genetics, gender,and lifestyle. Some of us inherit denser bones than others. For example, African Ameri-cans have denser bones than Caucasians. Men are larger and heavier than women andtherefore have a greater peak bone mass and a lower risk of fractures from osteoporosis.

F I G U R E 9 . 1 4

Our bones show up on X-rays because theyare denser than the soft tissue around them,but they are not as solid as rocks. (GustoProductions/Photo Researchers)

RememberThe important role of vitamin C insynthesizing collagen and the importanceof vitamin D for absorbing calcium fromthe diet are discussed in Chapter 8.

*

Peak bone mass The maximum bonedensity attained at any time in life, usuallyoccurring in young adulthood.

�*

Osteoporosis A bone disordercharacterized by a reduction in bone mass,increased bone fragility, and an increasedrisk of fractures.

�*

F I G U R E 9 . 1 5

Osteoporosis causes a decrease in bone densityand increases the risk of fractures. Normal bone(right). Bone weakened by osteoporosis (left).(Dr. Michael Klein/Peter Arnold, Inc.)

Lifestyle factors that affect bone mass include smoking, alcohol consumption, exercise,and diet. Smoking and alcohol consumption can decrease bone mass, whereas weight-bearing exercise, such as walking and jogging, increases bone mass. Having more body fatdecreases the risk of osteoporosis because adipose tissue produces estrogen, which helpsmaintain bone mass and enhances calcium absorption. A greater body weight also in-creases the amount of weight-bearing exercise that an individual gets in day-to-day activi-ties, which increases bone mass. Diet also affects bone mass. Adequate calcium intake,particularly while bone is being formed, allows greater peak bone mass.

Bone loss occurs with age and increases in women atmenopause Bone loss is a normal part of aging. Age-related bone loss occurs in bothmen and women, but women lose additional bone for about 5 years after menopause. Thispostmenopausal bone loss is related to declining estrogen levels, which affect bone cells anddecrease intestinal calcium absorption. Postmenopausal bone loss is one of the reasons os-teoporosis is a greater threat for women. Osteoporosis-related fractures occur in one out ofevery two women over age 50 and in about one in every eight men over 50 (Figure 9.16).11

The incidence of osteoporosis in African American women is half that of Caucasianwomen. The reason for this difference is that African American women not only havehigher peak bone mass, but also lower rates of bone loss after menopause.13

It is easier to prevent osteoporosis than to treat itOnce osteoporosis has occurred, it is difficult to restore lost bone. Therefore, the besttreatment for osteoporosis is to prevent it by achieving a high peak bone mass. A lowcalcium intake is the most significant dietary factor contributing to osteoporosis. Lowcalcium intake during the years of bone formation results in a lower peak bone massand, along with it, an increase in the risk of osteoporosis. A diet adequate in calciumand vitamin D and not excessive in phosphorus, protein, or sodium will reduce risk.Maintaining an active lifestyle that includes weight-bearing exercise and limits smok-ing and alcohol consumption will help to further improve bone density.

Osteoporosis is commonly treated with estrogen to increase calcium absorptionalong with supplements of calcium and vitamin D and regular weight-bearing exer-cise. Other treatments include other hormones and drugs that increase calcium ab-sorption or decrease bone loss; these are enhanced by calcium supplementation.14

Increased intakes of vitamin K, magnesium, fluoride, and boron are less effective buthave also been used to prevent and treat bone loss.

Calcium Is the Most Abundant Mineral in the Body 297

F I G U R E 9 . 1 6

Bone loss due to osteoporosis can cause astooped posture and a decrease in stature.(Larry Mulvehill/Photo Researchers)

For more information onthe incidence and risksof osteoporosis, go tothe National Institutes of

Health Osteoporosis andRelated Bone Disease National

Resource Center at www.osteo.org/

Calcium Is the Most Abundant Mineral in the Body

In an average person about 1.5% of body weight is calcium and 99% of this calciumis found in bone. The remaining calcium is located in body fluids where it performsother essential functions. For example, it is needed for cell communication and theregulation of body processes. Calcium helps regulate enzyme activity and is necessaryfor blood clotting. It is needed for the release of neurotransmitters, which allow nerveimpulses to pass from one nerve to another and from nerves to other cells. Inside themuscle cells, calcium allows the two muscle proteins, actin and myosin, to interact tocause muscle contraction. Calcium also plays a role in blood pressure regulation, pos-sibly by controlling the contraction of muscles in the blood vessel walls and signalingthe secretion of substances that regulate blood pressure.

Calcium levels are carefully regulatedThe roles of calcium are so vital to survival that powerful regulatory mechanisms ensurethat normal concentrations are maintained both inside and outside of cells. Slight changesin blood calcium levels trigger the release of hormones that work to keep calcium levels


P I E C E I T T O G E T H E R

A Diet for More Than Healthy Blood PressureJoshua is a 41-year-old father of three children. His father died ofa stroke at the age of 54 as a result of undiagnosed and untreatedhigh blood pressure. Joshua wants to live to see his grandchildren,so he exercises as often as he can, about three times a week, hasstopped smoking, and watches his diet and weight. Despite theseefforts, at his recent physical his blood pressure was elevated to138/89. Rather than start him on medication, his doctor

suggested a dietary approach first and referred him to a dietitian.A record of his diet from the previous day reveals that Joshua ismaintaining a normal body weight of 175 pounds by consumingabout 2500 Calories per day. After evaluating Joshua’s currentdiet, the dietitian recommends he follow the DASH diet to reducehis blood pressure. Joshua’s diet is shown here along with amodified diet that incorporates the dietitian’s recommendations.

Current Diet Modified Diet

Breakfast BreakfastOrange juice 3/4 cup Orange juice 3/4 cup1% low-fat milk 1 cup 1% low-fat milk 1 cupWheaties w/1 tsp sugar 1 cup Wheaties w/1 tsp sugar 1 cup

Banana 1 mediumWhole wheat bread w/jelly 1 slice Whole wheat bread w/jelly 2 slicesMargarine 1 tsp Margarine 1 tsp

Lunch LunchTuna salad 3/4 cup Tuna salad 3/4 cupWheat bread 2 slices Whole wheat bread 2 slices

Carrot sticks 1/2 cupBell pepper strips 1/2 cup

Chips 1 oz Fruit cocktail (light syrup) 1/2 cupCola 1 can 1% low-fat milk 1 cup

Dinner DinnerBaked chicken 3 oz Chicken in a stir fry with 3 oz

Almonds 10Broccoli 1/2 cupMushrooms 1/2 cup

Rice 1 cup Brown rice 1 1/2 cupSalad 1 cup Salad 1 cupLight salad dressing 1 Tbsp Light salad dressing 1 TbspDinner roll 1 Dinner roll 1Margarine 2 tsp Margarine 2 tspCantaloupe 1/2 cup Cantaloupe 1/2 cupIced tea (sweetened) 12 oz 1% low-fat milk 1 cup

Snacks SnacksCookies 2 large Frozen yogurt 1/2 cupDried apricots 5 Dried apricots 5Milky Way candy bar 1 Graham crackers 2Cola 1 can


HOW DO JOSHUA’S CURRENT DIET AND THE MODIFIEDDIET COMPARE TO THE RECOMMENDATIONS

OF THE FOOD GUIDE PYRAMID?

Your answer:

HOW DO THE CHANGES IN JOSHUA’S DIET AFFECTHIS INTAKE OF SODIUM AND POTASSIUM?

His original diet was not high in sodium, containingabout 2300 mg, which is slightly below the Daily Value of 2400 mg but above the DRI recommendation of 1500mg. The changes in his diet reduce his sodium slightly butincrease his potassium intake from 2870 mg to 5000 mg.The amount of magnesium is also increased slightly.

Joshua’s wife Yuka is 42 years old. Although she is notconcerned about her blood pressure, Yuka is concernedabout osteoporosis because her mother was recentlyhospitalized with a hip fracture. She wants to make sureshe is consuming adequate calcium. She is mildly lactoseintolerant.

IF YUKA CONSUMED THE MODIFIED DIET,WOULD IT MEET HER AI FOR CALCIUM?

Yes, her AI is 1000 mg, and the modified diet contains 1320 mg of calcium.

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Because of her lactose intolerance, Yuka does not drinkmuch milk. She can tolerate a small amount on her morningcereal and can consume yogurt and cheese in moderateamounts. If the milk consumed at lunch and dinner iseliminated from her diet, she would not meet the AI.

WHAT CHANGES WOULD INCREASE THE AMOUNTOF CALCIUM FROM LOW-LACTOSE SOURCES?

To increase calcium, Yuka could substitute canned salmonfor tuna in the salad at lunch. She could also include moretofu in her diet—a food she ate frequently while growingup in Japan. Including a serving of miso soup with tofu, orusing tofu instead of chicken in the stir fry at dinner wouldincrease calcium by about 130 mg. She can also replace themilk with small amounts of yogurt and low-fat cheese. Shemight also consider taking a calcium supplement.

Yuka only weighs 110 pounds and requires about 1800Calories to maintain her body weight.

HOW COULD THIS DIET BE CHANGED TO REDUCE THEENERGY CONTENT WITHOUT REDUCING THE CALCIUM?

Your answer:

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constant. When calcium levels drop, parathyroid hormone (PTH) is released. PTH has mul-tiple actions, which get more calcium into the blood and help keep it there. PTH stimu-lates the release of calcium from bone. It also stimulates the kidneys to activate vitamin D.Activated vitamin D increases the amount of dietary calcium absorbed from the gastroin-testinal tract and acts alongside parathyroid hormone to stimulate calcium release from thebone. PTH also acts in the kidneys to reduce the amount of calcium lost in the urine,thereby conserving the calcium already present in the blood. The overall effect of PTH isto rapidly increase blood calcium levels (Figure 9.17). If blood calcium levels become toohigh, PTH secretion is shut off and calcitonin is released. Calcitonin acts primarily onbone to inhibit the release of calcium, resulting in a decrease in blood calcium levels.

Calcium absorption depends on diet, age, and life stageDietary calcium is absorbed from the intestine by both active transport and passivediffusion. Active transport depends on the active form of vitamin D and accounts formost absorption in a meal with low to moderate amounts of calcium. When calciumintake is high, passive transport becomes more important. The efficiency with whichcalcium is absorbed also depends on dietary factors that block absorption and the lifestage of the individual.

Absorption can be helped or hindered by other dietarycomponents Because of vitamin D’s role in the active transport of calcium, it isthe nutrient that has the most significant impact on calcium absorption. When it isabsent, less than 10% of dietary calcium may be absorbed compared to the typical25% that is absorbed when it is present. The addition of vitamin D to milk thereforemakes sure the calcium in the milk can be absorbed efficiently.

Other substances present in foods, including oxalates, fiber, phytates, and tannins, in-terfere with calcium absorption. For example, spinach is a high-calcium vegetable butonly about 5% of the calcium is absorbed; the rest is bound by oxalates and excreted inthe feces.15 Vegetables such as kale, collard greens, turnip greens, mustard greens, andChinese cabbage are low in oxalates so their calcium is well absorbed. Chocolate also con-tains oxalates, but chocolate milk is still a good source of calcium because the amount ofoxalates from the chocolate added to a glass of milk is small. Fiber can also reduce calciumabsorption but, with a few exceptions, the effect is small. Phytates, however, can have asignificant effect on the absorption of calcium from foods such as wheat bran and pinto,

Activatesvitamin D

Increasesintestinal calcium

absorption

NORMALBLOOD

CALCIUM

LOW BLOODCALCIUM

Parathyroidhormone

Reducescalcium lost

in urineStimulatescalcium release

from bone

Parathyroid hormone (PTH) Ahormone secreted by the parathyroidgland that acts to increase blood calcium levels.

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Calcitonin A hormone produced bythe thyroid gland that stimulates bonemineralization and inhibits bone breakdown,thus lowering blood calcium levels.

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F I G U R E 9 . 1 7

When blood levels of calcium drop they are quickly restoredto normal by the actions of parathyroid hormone.


YOGURT

Salmon

1 Cup 2% milk300mg Ca

120 Cal

6 cupsKidney beans

1350 Cal

7 ozTofu

160 Cal

2 ozCheddar cheese

230 Cal

2 cupsIce cream545 Cal

11 slicesWhite bread

730 Cal

5 ozCanned salmon

200 Cal

3/4 cupFruit yogurt

190 Cal

11/3 cupCooked collards

66 Cal

F I G U R E 9 . 1 8

This figure illustrates the amounts of various foods that you wouldneed to eat to obtain the same amount of calcium as one cup ofreduced fat milk.

red, and white beans. You would need to eat almost 10 servings of red beans or 16 serv-ings of spinach to absorb the same amount of calcium as you would from 1 cup of milk.When calcium intake is low, these dietary components may reduce absorption enough toaffect calcium status, but when calcium intake is adequate, their effect is insignificant.16

Calcium absorption is higher when bones are growingCalcium absorption is higher at times of life when the need is the greatest. During in-fancy, about 60% of calcium consumed is absorbed. In young adults absorption isabout 25%. In older adults absorption declines in part due to a decrease in blood lev-els of the active form of vitamin D. An additional decrease in calcium absorption oc-curs in women after menopause due to the decrease in estrogen.

During pregnancy, when calcium is needed for formation of the fetal skeleton, cal-cium absorption increases to over 50% during the 5th or 6th month of gestation. Cal-cium need is also increased during lactation, but some of the calcium needed to makemilk appears to come from the mother’s bones. After lactation, an increase in calciumabsorption and retention of calcium by the kidneys help restore bone calcium.

You need enough calcium to support bonegrowth and maintenanceHow much calcium do you need? Early in life you need enough to support bonegrowth. Therefore the DRI recommendations are higher for children than adults. Anintake of 1300 mg per day is recommended for growing children and adolescentswhen peak bone mass is being achieved; this recommendation drops to 1000 mg perday for adults age 19 through 50 years. Absorption decreases with age, so later in lifethe recommendation is increased again, this time to 1200 mg per day for those age 51and older to maintain bone and prevent fractures from osteoporosis.14

Dairy products are the best source of calcium in theAmerican diet The main source of calcium in the North American diet is milk,yogurt, cheese, and other dairy products. Fish such as sardines that are consumed intheir entirety, including the bones, are also a good source, as are legumes and some greenvegetables such as mustard greens, Chinese cabbage, kale, and broccoli (Figure 9.18).Grains are only a moderate source of calcium, but because they are consumed in such

It is estimated that only 25% ofboys and 10% of girls consume therecommended amount of calciumand only 50 to 60% of adults meetthe recommendation.


large quantities they make a significant contribution to dietary calcium intake. Adequatecalcium intake can be achieved by following the Food Guide Pyramid recommendationof two to three servings of milk, yogurt, or cheese daily plus three to five servings of veg-etables a day.

Some of the calcium in our diet is added to foods during processing. For example,many baked goods such as breads, rolls, and crackers, have added nonfat dry milkpowder, which provides calcium. Tortillas that are treated with lime water (calciumhydroxide) and tofu made with calcium sulfate are good sources of calcium. In addi-tion, there are many products on the market, such as orange juice and breakfast cere-als, that are fortified with calcium (Table 9.5).

Calcium supplements can help meet calcium needs Indi-viduals who do not meet their calcium needs with diet alone can benefit from cal-cium supplementation. In young individuals supplemental calcium can increasepeak bone mass. In postmenopausal women, calcium supplements are not effectiveat increasing bone mass but they can help reduce bone loss.17 Because calcium ab-sorption decreases when large amounts (500 mg or more) are consumed at onetime, it is better to take a lower-dose calcium supplement (no more than 500 mgper dose) twice a day than to take a once-a-day supplement that provides 100% ofthe AI. What you take with your supplement also affects the availability of the cal-cium and of other minerals in the diet. Acidic foods, lactose, and fat increase cal-cium absorption, whereas oxalate, phytates, and fiber inhibit calcium absorption.The large amounts of calcium contained in a supplement can also interfere with theabsorption of iron, zinc, magnesium, and phosphorus, so supplements should betaken with care. Very high doses can also cause kidney stone formation and kidneyinsufficiency. A UL of 2500 mg per day from food and supplements has been set foradults ages 19 to 70 years.

T A B L E 9 . 5Finding Good Sources of Calcium

What the Label Says What It Means

High-calcium, rich in calcium, Contains 200 mg of calcium or more per excellent source of calcium serving

Good source of calcium Contains 100 mg to 190 mg of calcium perserving

More or added calcium Contains at least 100 mg more of calcium perserving than a reference food

Milk may do more than add calciumfor healthy bones. A recent studycomparing the amount of weight lostby subjects consuming a low-caloriediet found that those who includedthree to four servings of dairyproducts daily lost more weight thanthose who supplemented calcium or consumed a low-dairy diet (Obes. Res. 12:582–590, 2004).

Phosphorus Is Found in Bone and Almost Everywhere Else

Most of the phosphorus in your body is found with calcium in bones and teeth as partof the hard mineral crystals. The smaller amount of phosphorus in soft tissues hasboth structural and regulatory roles. It is a component of phospholipids, which formthe structure of cell membranes. It is a major constituent of DNA and RNA, whichorchestrate the synthesis of proteins. Phosphorus is also involved in regulating enzymeactivity because the addition of phosphorus as phosphate can activate or inactivatecertain enzymes. The high-energy bonds of ATP are formed between phosphategroups. Phosphorus is also part of a buffer that helps regulate intracellular acidity sothat chemical reactions can proceed normally.

Buffer A substance that reacts with anacid or base to prevent changes in acidity.�*

Calcium and vitamin D intakes aresuch a concern in the United Statesthat some nutrition scientists havesuggested that they be added toenriched grains along with B vitaminsand iron.

Phosphorus Is Found in Bone and Almost Everywhere Else 303

Off the Label: Counting All Your Calcium?

Do you get enough calcium? You may consume it innatural sources such as milk, yogurt, and leafy greenvegetables. Or, you may choose calcium-fortified foods tohelp meet your needs. Perhaps you include a calciumsupplement just to be sure. To find out if you get enoughyou need to count all your calcium sources.

You can see if a packaged food is a good source bylooking at the label. All food labels list the % Daily Valuefor calcium in the Nutrition Facts panel. To calculate themilligrams of calcium in a food, multiply the % Daily Valueby 1000 mg (the Daily Value for calcium). For example, a boxof fortified breakfast cereal may show that a servingprovides 25% of the Daily Value for calcium. By multiplying25% by 1000 mg you can calculate that a serving provides250 mg of calcium. Foods high in calcium may include astatement that they are a good source of calcium as well asthe health claim that a diet high in calcium helps reduce therisk of osteoporosis.

The label on your milk carton indicates that an 8-ounceglass has 30% of your Daily Value for calcium. But, for anumber of reasons, many of us don’t drink milk, or drinkless than we should. Teenage girls concerned about theirweight will typically choose a diet soda over a glass of milk.The soda label says calorie-free, but it is also calcium-free.Twenty years ago boys and girls consumed more milk thansoft drinks, but today they consume twice as much soda popas milk. Teenage girls consume only 60% of therecommended amount of calcium, with soda drinkersconsuming almost one-fifth less calcium than non-sodadrinkers.1 Many older adults do not drink milk because theyare lactose intolerant, believe milk is for kids, or skimp onmilk to decrease their calorie intake.

If your calcium count from food comes up short, you canadd to your intake by choosing a supplement. Yourmultivitamin and mineral supplement will only provide asmall amount of the calcium you need; each pill would haveto be the size of a marble to give you enough calcium alongwith everything else it contains. To get a significant amountof your calcium from a supplement, choose one thatcontains calcium alone or calcium with vitamin D. Vitamin Dis commonly included in calcium supplements because it aidscalcium absorption. The Supplement Facts label will tell youhow much of each nutrient is included in your supplement.If you choose a product that contains vitamin D you need tobe sure to monitor the amount of vitamin D, because it canbe toxic in large amounts. If you double your calcium dose,you will get twice as much vitamin D.

The form of calcium used in supplements is alsoimportant. Calcium carbonate is absorbed as well as thecalcium from milk, and the other forms, including calciumcitrate, calcium gluconate, calcium lactate, calcium citrate-malate, and calcium phosphate, are absorbed as well ascalcium from a mixed diet.2 Calcium preparations such asbone meal, coral calcium, powdered bone, dolomite(limestone), and oyster shell should be avoided because theymay contain enough contaminants to be dangerous ifconsumed routinely.3

Some calcium supplements are also over-the-counterantacids. These will have a Drug Facts, rather than aSupplement Facts label (see Chapter 3, Antacids: Getting theDrug Facts). Some of these, such as Tums, which containscalcium carbonate, are safe, effective calcium supplements.However, antacids that contain aluminum and magnesiummay actually increase calcium losses from the body.

To see if you are getting enough calcium, you need tocheck the labels on your foods, supplements, and drugs;consider the form of calcium in each; and watch for excessesof other nutrients and contaminants. Sound complicated?Maybe an extra glass of milk is an easier choice.

References1. Center for Science in the Public Interest. Liquid candy highlights. Available

online at www.cspinet.org/sodapop/highlights.htm/Accessed August 23, 2004.2. Mortensen, L., and Charles, P. Bioavailability of calcium supplements and the

effect of vitamin D: Comparisons between milk, calcium carbonate, and calciumcarbonate plus vitamin D. Am. J. Clin. Nutr. 63:354–357, 1996.

3. Bourgoin, B. P., Evans, D. R., Cornett, J. R., et al. Lead content in 70 brands ofdietary calcium supplements. Am. J. Public Health 83:1155–1160, 1993.(George Semple)


Phosphorus levels are regulated to promotebone healthBlood levels of phosphorus are not as strictly controlled as those of calcium, but levelsare maintained in a ratio with calcium that allows minerals to be deposited into bone.Phosphorous is more easily absorbed than calcium. About 60 to 70% is absorbed from atypical diet. Vitamin D enhances phosphorous absorption, but enough can be absorbedeven when vitamin D is absent. The regulatory mechanisms that increase calcium ab-sorption at the intestine and increase calcium release from bone have similar effects onphosphorus. Therefore low calcium will cause an increase in both calcium and phospho-rus absorption and release both calcium and phosphorus from bone. The kidney is im-portant for regulating phosphorus levels; when blood phosphorous levels increase theamount lost in the urine also increases to keep blood levels in the normal range.

It is not difficult to get enough phosphorus in your dietIt is easy to find good dietary sources of phosphorus. Dairy products such as milk, yo-gurt, and cheese, as well as meat, cereals, bran, eggs, nuts, and fish are all good sources(Figure 9.19). Food additives used in baked goods, cheese, processed meats, and softdrinks also provide phosphorus. Because phosphorus is so widely distributed in food,dietary deficiencies are rare. Most diets meet the RDA of 700 mg per day for adults.14

Marginal phosphorus status may be caused by losses due to chronic diarrhea and over-use of aluminum-containing antacids, which prevent phosphorus absorption. Phos-phorus deficiency can lead to bone loss, weakness, and loss of appetite.

Toxicity from high phosphorus intake is rare in healthy adults, but excessive in-takes can lead to bone resorption. Levels of phosphorus intake typical in the UnitedStates are not believed to affect bone health as long as calcium intake is adequate. TheUL for phosphorus is 4.0 grams per day for adults.14

Phosphorus (mg)

RDA

0 700

Sunflower seeds (1/4 c)Walnuts (1/4 c)

Garbanzo beans (1 c)Tofu (1/2 c)Beef (3 oz)

Sardines, canned (3 oz)Chicken (3 oz)

1% milk (1 c) Cheese, cheddar (1.5 oz)

Yogurt (1 c)Orange (1 med)

Kiwi (2 med)Apple (1 med)

Carrots (1 c)Broccoli (1 c)

Kale, cooked (1 c)Potato (1 med)

Oatmeal (1 c)Spaghetti (1 c)

White bread (2 sl)Whole-wheat bread (2 sl)

600500400300200100

F I G U R E 9 . 1 9

Phosphorus content of selections from each group of the Food Guide Pyramid. The dashed line represents the RDA for adults. As with calcium, dairy products are goodsources of phosphorus. Unlike calcium, phosphorus is plentiful in a variety of other foods. (Brian Hagiwara/Food Pix)

Magnesium Is Needed in Bone and Body Fluids

Magnesium Is Needed in Bone and Body Fluids 305

Magnesium (mg)

RDA

Sunflower seeds (1/4 c)Almonds (1/4 c)

Garbanzo beans (1 c)Tofu (1/2 c)Beef (3 oz)

Sardines, canned (3 oz)Chicken (3 oz)

1% milk (1 c) Cheese, cheddar (1.5 oz)



Carrots (1 c)Broccoli (1 c)

Spinach, cooked (1 c)Potato (1 med)



0 400100 200 300

F I G U R E 9 . 2 0

Magnesium content of selections from each group of the Food Guide Pyramid. The dashed line represents the RDA for adult men age 31 and older. Leafy greens such asspinach are excellent sources. (Corbis Images)

Magnesium is far less abundant in the body than calcium or phosphorus, but it is stillessential for healthy bones. About 50 to 60% of the magnesium in the body is in bonewhere it is essential for maintaining structure. The rest of the magnesium is found incells and fluids throughout the body. The kidneys regulate blood levels of magnesium.When intake is low, excretion in the urine is decreased. As intake increases, urinary ex-cretion increases to maintain normal blood levels.

Magnesium functions in over 300 reactionsIn addition to its role in bone structure, magnesium is involved in regulating calciumhomeostasis and is needed for the action of vitamin D and many hormones includingPTH.18 Magnesium is important for blood pressure regulation and may play a role inmaintaining cardiovascular health. In addition, magnesium is involved in chemical reac-tions throughout metabolism including those necessary for the generation of energy fromcarbohydrate, lipid, and protein (see Table 9.1). In some of these reactions it is an enzymeactivator, but it is also needed to stabilize ATP, so every reaction that generates or usesATP requires magnesium. It is important for the functioning of the nerves and musclesbecause it is needed to transport sodium and potassium across cell membranes. It isneeded to allow muscles to relax after a contraction. Because it is involved in DNA, RNA,and protein synthesis, magnesium is particularly important for dividing, growing cells.

We get magnesium from greens and whole grainsMagnesium is found in many foods but in small amounts, so you can’t get all youneed from a single food. It is found in leafy greens such as spinach and kale because itis a component of the green pigment chlorophyll. Nuts, seeds, bananas, and the germand bran of whole grains are also good sources of magnesium (Figure 9.20). Processed


foods are generally poor sources. For example, removing the bran and germ of thewheat kernel reduces the magnesium content of a cup of white flour to only 28 mg,compared with the 166 mg in a cup of whole wheat flour. “Hard” water, which is highin calcium and magnesium, can be a significant source. Magnesium absorption is en-hanced by the active form of vitamin D and decreased by the presence of phytates andcalcium.

The RDA for magnesium is 400 mg per day for young men and 310 mg per dayfor young women.14 A deficiency can cause nausea, muscle weakness and cramping,irritability, mental derangement, and changes in blood pressure and heartbeat. Lowblood magnesium levels affect levels of blood calcium and potassium; therefore someof these symptoms may be due to alterations in the levels of these other minerals.

Magnesium deficiency is rare in the general population. However, it does occur inthose with alcoholism, malnutrition, kidney disease, and gastrointestinal disease, aswell as in those who use diuretics that increase magnesium loss in the urine. Marginalintakes of magnesium have been associated with a number of chronic diseases includ-ing osteoporosis, atherosclerosis, and high blood pressure.

No adverse effects have been observed from magnesium consumed in foods, buttoxicity may occur from concentrated sources such as magnesium-containing drugs,like milk of magnesia and magnesium-containing supplements. Magnesium toxicitycauses nausea, vomiting, low blood pressure, and other cardiovascular changes. TheUL for adults and adolescents over 9 years of age is 350 mg of nonfood magnesium.


To get calcium into your body and your bones• Drink your milk!• Have at least one serving of a leafy green vegetable a day• Bone up on calcium by having sardines or canned salmon, which are eaten with the bones• Taste some tofu• Snack on yogurt; ounce for ounce it has more calcium than milk• Walk, jog, or jump up and down—weight-bearing exercises build up bone

Don’t fret about phosphorus—it’s in almost everything you eat

To maximize your magnesium• Have whole grains• Sprinkle nuts and seeds on salads, cereals, and stir fries• Go for the green—whenever you eat green you are eating magnesium and most greens contain

calcium too

The incidence of heart attacks islower in areas that have hard water,which is water that has a highcontent of minerals such as calciumand magnesium.

Iron Is Needed to Transport Oxygen to Body Tissues

Iron is good for your blood. We have known since the 18th century that iron is amajor constituent of blood. By 1832, iron tablets were used to treat young women inwhom “coloring matter” was lacking in the blood. Today we know that the red colorin blood is due to the iron-containing protein hemoglobin (Table 9.6). The hemoglo-bin in red blood cells transports oxygen to body cells and carries carbon dioxide awayfrom cells for elimination by the lungs. Most of the iron in the body is part of hemo-globin but iron is also needed for the production of a number of other iron-contain-ing proteins. It is part of myoglobin found in muscle, where it enhances the amount

Hemoglobin An iron-containingprotein in red blood cells that binds oxygenand transports it through the bloodstreamto cells.

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Iron Is Needed to Transport Oxygen to Body Tissues 307

T A B L E 9 . 6A Quick Summary of the Trace Elements



Iron Red meats, 8–18 mg/day Part of hemoglobin, Fatigue, Infants and Gastrointestinalleafy greens, which delivers weakness, small preschool upset,dried fruit, oxygen to cells, pale red blood children, liver damage;whole and myoglobin, which cells, low adolescents, UL is 45 mgenriched holds oxygen in hemoglobin women ofgrains muscle, and (iron deficiency childbearing

compounds anemia) age, pregnantneeded in energy women, athletesproduction and immune function

Copper Organ meats, 900 �g/day A part of proteins Anemia, poor Those who over- Vomiting;nuts, seeds, needed for iron growth, bone supplement zinc UL is 10 mgwhole grains, absorption, lipid abnormalitiesseafood, metabolism, cocoa collagen synthesis,

nerve and immunefunction, and antioxidant protection

Zinc Meat, 8–11 mg/day Regulates protein Poor Vegetarians, Decreasedseafood, synthesis; functions growth and low-income copperwhole in growth, development, children, elderly absorption,grains, eggs development, skin rashes, depressed

wound healing decreased immuneimmunity, and immune function; ULantioxidant function is 40 mgprotection

Selenium Organ 55 �g/day Antioxidant Muscle pain, Populations in Nausea,meats, protection as part weakness, a areas with low- diarrhea,seafood, of glutathione form of heart selenium soil vomiting,eggs, whole peroxidase, disease fatigue, hairgrains synthesis of changes; UL

thyroid hormones is 400 �g

Iodine Iodized salt, 150 �g/day Needed for Goiter, Populations Enlargedsalt water synthesis of cretinism, in areas with thyroid; UL is fish, seafood, thyroid hormones mental low-iodine soil 1110 �gdairy retardation, and where products growth and iodized salt is

developmental not usedabnormalities

Chromium Brewers 25–35 �g/day Enhances High blood Malnourished None reported;yeast, nuts, insulin action glucose children no ULwhole grains,mushrooms

Fluoride Fluoridated 3–4 mg/day Strengthens tooth Increased risk Populations in Mottled water, tea, enamel, enhances of dental caries areas with teeth, kidney fish, remineralization of unfluoridated damage, bonetoothpaste tooth enamel, water abnormalities;

reduces acid UL is 10 mgproduction bybacteria in the mouth (Continued)


of oxygen available for use in muscle contraction. It is also essential for energy produc-tion as a part of several proteins needed in aerobic metabolism. Iron-containing pro-teins are involved in drug metabolism and the immune system. Iron is also acomponent of the enzyme catalase, which protects the cell from oxidative damage.

Iron deficiency causes weakness and fatigueWhen iron is deficient, hemoglobin cannot be produced. When not enough hemoglo-bin is available, the red blood cells that are formed are small and pale and unable todeliver adequate oxygen to the tissues. This is known as iron deficiency anemia (Figure9.21a). Symptoms of iron deficiency anemia include fatigue, weakness, headache, de-creased work capacity, an inability to maintain body temperature in a cold environ-ment, changes in behavior, decreased resistance to infection, impaired development ininfants, and an increased risk of lead poisoning in young children. Anemia is the laststage of iron deficiency. Earlier stages have no symptoms because they do not affectthe amount of iron in red blood cells but they can be detected by blood tests thatmeasure levels of iron in the plasma and in body stores (Figure 9.21b).

Despite the fact that iron is one of the best understood of the trace elements, irondeficiency anemia is the most common nutritional deficiency in the United States andworldwide.19 In the United States, it affects 7.8 million adolescent girls and women ofchildbearing age and 700,000 children between the ages of 1 to 2 years. The incidenceis greatest among low-income and minority women and children. Worldwide it is esti-mated that over 2 billion people suffer from iron deficiency anemia and another 3 bil-lion have deficient iron stores.20

Absorption regulates how much iron is in the bodyIron is not easily eliminated from the body so iron level is regulated primarily by ad-justing the amount of iron that is absorbed. How much iron reaches body cells de-pends on the form of iron in the diet and the body’s need.

Iron from animal sources is better absorbed Iron in the dietcomes from both plant and animal sources. Much of the iron in animal products ispart of a chemical complex called heme iron, which is found in certain proteins suchas myoglobin and hemoglobin. The best sources of heme iron are red meats and organmeats such as liver and kidney (Figure 9.22). Heme iron is absorbed more than twiceas efficiently as nonheme iron. The iron found in plant sources such as leafy green

One strange symptom that isoccasionally associated with irondeficiency is pica. Pica is acompulsion to eat nonfood itemssuch as clay, ice, paste, laundrystarch, paint chips, and ashes.Sometimes the things consumedcontain toxic minerals, such as leador substances that inhibit mineralabsorption.

Iron deficiency anemia A conditionthat occurs when the oxygen-carryingcapacity of the blood is decreasedbecause there is insufficient iron to makehemoglobin. It is diagnosed in adultswhen hemoglobin concentration is lessthan 11 grams per 100 ml of blood.

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T A B L E 9 . 6A Quick Summary of the Trace Elements (Continued)



Manganese Nuts, 1.8–2.3 mg/day Functions in Growth None Nervelegumes, carbohydrate retardation damage; ULwhole and lipid is 11 mggrains, tea metabolism

and antioxidantprotection

Molybdenum Milk, organ 45 �g/day Aids the action Unknown None Arthritis andmeats, of a number of in humans jointgrains, enzymes inflammation;legumes UL is 2 mg

Heme iron A readily absorbed formof iron found in animal products that ischemically associated with proteins suchas hemoglobin and myoglobin.

�*


Iron stores

Adequateiron

status

Normal Depletion Deficiency

Low ironstores

Depletediron stores

Iron Status

Low levelsof circulating

iron

Irondeficiency

anemia

Iron in plasma

Iron in RBCs

F I G U R E 9 . 2 1

(a) Iron deficiency anemia occurs whenthere is not enough iron to synthesizeadequate amounts of hemoglobin. It causesthe red blood cells to become small andpale. Normal red blood cells are shown onthe left and those typical of iron deficiencyanemia are illustrated on the right. (b) Irondeficiency anemia is the final stage of irondeficiency. Inadequate iron first causes adecrease in the amount of stored iron,followed by low iron levels in the plasma. Itis only after plasma levels drop that there isno longer enough iron available to maintainhemoglobin in red blood cells. (a: B&BPhotos/Custom Medical Stock Photo, Inc.;b; Custom Medical Stock Photo, Inc.)

Iron (mg)

RDA

987654321


Lentils (1 c)Beef (3 oz)

Salmon (3 oz)Chicken (3 oz)

1% milk (1 c)Cheese, cheddar (1.5 oz)


Kiwi (2 med)Apple (1 med)Raisins (1/2 c)

Tomato (1 med)Broccoli, cooked (1 c)Spinach, cooked (1 c)

Potato, baked (1 med)Oatmeal (1 c)

Spaghetti (1 c)White bread (2 sl)

Whole-wheat bread (2 sl)

10

F I G U R E 9 . 2 2

Iron content of selections from each group of the Food Guide Pyramid. The dashed line represents the RDA for adult men and postmenopausal women. Both plant andanimal foods are good sources of iron, but the heme iron in animal foods is more readily absorbed. (Tony Freeman/PhotoEdit)

(a) (b)


Nucleus

Iron is lostwhen celldies

Lumen ofsmall intestine

iron

Ferritin Nucleus

Transferrin

Mucosalcells

BloodBone marrow,liver, and othertissue

Iron

iron

F I G U R E 9 . 2 3

Iron that enters the mucosal cells of the small intestine may either be bound to ferritin ortransported in the blood by the protein transferrin. Iron trapped in the mucosal cell byferritin is lost when the cell dies. Iron transported by transferrin reaches body cells thatneed iron. When iron levels are high, more iron is stored as ferritin.

For more information oniron deficiency anemia,go to the World HealthOrganization Web site

at www.who.int/nut/

vegetables like spinach and kale, legumes, and grains is nonheme iron. Animal foodsalso contain nonheme iron in addition to heme iron. Nonheme iron absorption canbe enhanced as much as sixfold by consuming it with foods rich in vitamin C. Con-suming beef, fish, or poultry in the same meal as nonheme iron also increases absorp-tion. For example, a small amount of hamburger in a pot of chili will enhance thebody’s absorption of iron from the beans. On the other hand, fiber, phytates, tannins,and oxalates prevent absorption by binding iron in the gastrointestinal tract. The pres-ence of other minerals may also decrease iron absorption.

Iron absorption depends on iron needs When iron is absorbed, itenters the cells of the small intestine. It can either be stored there or transported in theblood to other parts of the body. Stored iron is bound to the iron storage protein fer-ritin. Iron that is to be transported must first be bound to an iron transport proteincalled transferrin. When the iron-transferrin complex reaches body cells, it binds to aprotein on the cell membrane called a transferrin receptor, which allows the iron to betaken into the cell. When iron is in short supply, the number of transferrin receptors in-creases. Having more transferrin receptors allows more iron to be delivered to the cells.When iron is plentiful, the number of transferrin receptors decreases so less iron is deliv-ered to cells, while the amount of ferritin increases to enhance the ability to store iron.As a result, more iron is then left in the mucosal cells bound to ferritin and is thereforelost when the cells die and are sloughed into the intestinal lumen (Figure 9.23).

Iron is also stored as ferritin in other parts of the body, primarily the liver, spleen,and bone marrow. When ferritin concentrations in the liver become high, some isconverted to an insoluble storage protein called hemosiderin. Iron can be mobilizedfrom body stores as needed, and deficiency signs will appear only after stores are de-pleted (see Figure 9.21b).

Iron is lost primarily through blood loss Iron is not readily ex-creted. Even when red blood cells die, the iron in their hemoglobin is not lost fromthe body; the iron is recycled and can be incorporated into new red blood cells. Mostiron lost even in healthy individuals occurs through blood loss, including that lostduring menstruation and the small amounts lost from the gastrointestinal tract. Someiron is also lost through the shedding of cells from the intestine, skin, and urinarytract.

Women require more iron than menIron is the only nutrient for which the recommended intake is greater for youngwomen than it is for young men. The RDA for iron for menstruating women is 18mg per day, but for adult men it is only 8 mg per day. The greater need is due to theiron lost in menstrual blood. Only about one-fourth of adolescent girls and women ofchildbearing age meet the RDA for iron through their diet.19 After menstruation stopsthe need for iron decreases, so the requirement for postmenopausal women is the

Ferritin The major iron storageprotein.�*

Transferrin An iron transport proteinin the blood.�*

same as for adult men. The RDA for iron assumes that the diet contains both plantand animal sources of iron.21 A separate RDA category was created for vegetarians andthese recommendations are higher to account for the poorer iron absorption fromplant sources (Table 9.7).

The risk of iron deficiency is increased in groups whose needs are higher. Pregnantwomen are at risk because the need for iron is increased due to the increase in maternalblood volume and the growth of other maternal tissues and the fetus. Iron deficiency iscommon among pregnant women even in industrialized countries and can lead to pre-mature delivery and greater risk to the mother. Iron deficiency is also common in in-fants, children, and adolescents because their rapid growth increases iron needs. Athletesare another group susceptible to iron deficiency. The DRIs suggest that athletes’ ironneeds may be 30 to 70% higher than the general population (see Chapter 11).

To meet needs consider the amount and bioavailability of ironSomeone who consumes 2 to 3 servings of meat, fish, or poultry a day is getting about5 to 8 mg of iron, much of which is highly absorbable heme iron. If you are not a meateater you can meet your iron needs from plant sources. A peanut butter sandwich and abox of raisins provide 3.3 mg. The amount of iron absorbed from these foods is lower,but can be increased if you include a source of vitamin C with the meal. For example,you could add orange sections to your lunch or have strawberries for dessert. You can


T A B L E 9 . 7How Much Iron Do You Need?

Gender/Life Stage Recommended Intake

Infants0–6 months 0.27 mg*7–12 months 11 mgChildren1–3 years 7 mg4–8 years 10 mgMales9–13 years 8 mg14–18 years 11 mg� 19 years 8 mgFemales9–13 years 8 mg14–18 years 15 mg19–50 years 18 mg� 51 years 8 mgFemales taking oral contraceptives14–18 years 11.4 mg19–50 years 10.9 mgPregnancy� 18–50 years 27 mgLactation� 18 years 10 mg19–50 years 9 mgVegetariansMen � 19 years 14 mgMenstruating women 33 mgAdolescent girls 26 mg

*This value is an AI; all other values are RDAs.


P I E C E I T T O G E T H E R

Adding to Your Iron IntakeHanna is a 23-year-old graduate student. She has been feelingtired and run down all semester. She recently read an articleabout iron deficiency in young women and became concernedabout her iron status. She decides to go to the health centerwhere she has blood drawn. The results of her tests indicate thatshe does not have iron deficiency anemia, but her iron stores arevery low.

A review of her typical diet shows that Hanna’s iron intake isless than the recommended amount. She decides to try toincrease the amount of iron she gets from her diet beforeconsidering iron supplements. Hanna is from SouthCarolina and consumes a primarily vegetarian diet. At homeher mother prepared meals in iron cookware, but the pans inHanna’s college apartment are stainless steel. Her typical dietis shown below.

Typical DietFood Amount Iron (mg)

BreakfastGrits with 1 cup 0.5

butter 1 tsp 0Plantain 1 0.9Whole wheat toast 1 slice 1.2Apple juice 3/4 cup 0.7Tea with 1 cup 0

sugar 1 tsp 0

LunchApple 1 medium 0.2Cornbread with 1 piece 1.5

butter 1 tsp 0Yogurt 1 cup 0.2Tomato 1 medium 0.5Tea with 1 cup 0

sugar 1 tsp 0

DinnerRice 1 cup 2.4Peanuts 1/3 cup 0.9Kale 1 cup 1.2Yams 1 cup 1.1Apple juice 3/4 cup 0.7Tea with 1 cup 0

sugar 1 tsp 0

Total 12.0

DOES HANNA’S IRON INTAKE MEET THE RDA FOR A YOUNG FEMALE VEGETARIAN?

No. The RDA for a vegetarian woman who is menstruatingis 33 mg. Hanna’s diet only provides 12 mg.

WHAT OTHER DIETARY FACTORS COULD BECONTRIBUTING TO HANNA’S POOR IRON STATUS?

Your answer:

HOW COULD HANNA INCREASE THE IRONCONTENT OF HER DIET?

Hanna is a vegetarian, so her iron sources are limited toplant foods, which are generally lower in iron and containonly the less-well-absorbed nonheme form of iron. Thereare, however, good plant sources of naturally occurring ironas well as sources fortified with iron. For instance, switchingfrom the half cup of grits, containing about 0.5 mg of iron,to a fortified cereal will greatly increase her intake. Adding2 tablespoons of raisins to the hot cereal contributesanother 0.4 mg. Another good vegetarian source of iron isbeans. A bowl of chili with beans at lunch will add 8 mg ofiron. Cooking her meals in an iron skillet would add ironto foods cooked in it.

WHAT COULD HANNA DO TO INCREASE THE AMOUNTOF IRON ABSORBED FROM HER MEALS?

Your answer:

DOES HANNA’S DIET PROVIDE GOOD VEGETARIANSOURCES OF CALCIUM? ARE THERE OTHER NUTRIENT

DEFICIENCIES FOR WHICH SHE MAY BE AT RISK?

Your answer:

�

�

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also use iron-fortified foods to help meet your iron needs. Food labels can help identifyfoods that are good sources of iron. The iron content of packaged foods must be listedon food labels as a percent of the Daily Value. A serving of enriched grains providesanywhere from 4 to 10% of the Daily Value; a serving of fortified breakfast cereal maysupply 30, 40, or even 100% of the Daily Value.

Although diet is the ideal way to meet iron needs, supplements are often recom-mended for groups at risk for deficiency. Iron supplements typically contain nonhemeiron. Therefore, to enhance absorption, iron supplements should be consumed withfoods containing vitamin C, such as orange juice; taken with a meal containing meat,fish, or poultry; and not taken with dairy products or substances that bind iron. Ironsupplements should not be taken at the same meal as calcium supplements, which de-crease iron absorption. Large intakes of iron from supplements can interfere with theabsorption of zinc and copper. They can also cause stomach upset and constipation.Taking a fiber supplement can help alleviate constipation, but be aware that the fiberwill reduce iron absorption if these are taken at the same time.

Too much iron is toxicA single, large dose as well as more moderate doses of iron consumed over a longer periodof time can both cause toxicity symptoms. Acute iron toxicity from excessive consump-tion of iron-containing supplements is one of the most common forms of poisoningamong children under age 6. Accumulation of iron in the body over time, referred to asiron overload, generally occurs only in individuals with hereditary abnormalities in ironabsorption, diseases requiring frequent blood transfusions, or conditions in which redblood cell synthesis is abnormal. A UL has been set at 45 mg per day from all sources.

Even a single large dose can be life-threatening Iron poisoningmay cause damage to the intestinal lining, abnormalities in body acidity, shock, and liverfailure. Even a single large dose can be fatal. To protect children from accidental poison-ing, iron-containing products such as drugs and supplements are required to display awarning on the label (Figure 9.24). In addition, since most cases of serious iron poison-ing have occurred with products containing 30 mg or more per dose, these products arepackaged in individual doses to make consumption of many pills difficult for a youngchild.22 Iron-containing supplements should be taken only as suggested on the label andstored out of the reach of children or others who may consume them in excess.

Hemochromatosis is an inherited condition that leads toiron overload Hemochromatosis is a genetic disorder in which iron absorptionis increased. The accumulation of excess iron that occurs in hemochromatosis causes


Iron cooking utensils provide iron tothe body when it leaches into food.Leaching is enhanced by acidicfoods. For example, 3 ounces ofspaghetti sauce cooked in a glasspan contains about 0.6 mg of iron,but the same amount of saucecooked in an iron skillet containsabout 5.7 mg, depending on howlong it is cooked.

5 6789 34 00 34 5 2

WARNING: CLOSE TIGHTLY ANDKEEP OUT OF REACH OF CHILDREN.CONTAINS IRON, WHICH CAN BEHARMFUL OR FATAL TO CHILDRENIN LARGE DOSES. IN CASE OFACCIDENTAL OVERDOSE, SEEKPROFESSIONAL ASSISTANCE ORCONTACT A POISON CONTROLCENTER IMMEDIATELY.

F I G U R E 9 . 2 4

Labels on iron-containing supplements and medications must carry atoxicity warning.

Hemochromatosis An inheritedcondition that results in increased ironabsorption.

�*


oxidative changes resulting in heart and liver damage, diabetes, and certain types ofcancer. Iron deposits also darken the skin. To have these symptoms, an individualmust inherit the hemochromatosis gene from both parents. If you inherit the genefrom only a single parent you won’t have these serious symptoms, but you will absorbiron better than people who do not have the gene at all. The treatment for hemochro-matosis is simple: regular blood withdrawal. Iron loss through blood withdrawal willprevent the complications of iron overload, but to be effective it must be initiated be-fore organs are damaged. Therefore, genetic screening is essential to identify and treatindividuals before any damage has occurred.

Iron supplements can bedangerous because consumptionof excess iron can cause liverfailure. In fact, iron supplementoverdose is the leading cause ofliver transplants in children.

Much of what we know aboutcopper was discovered by studyingpeople who have a rare disordercalled Menke’s kinky hair syndromein which the ability to use copper isdefective.

Copper Deficiency Can Cause Iron Deficiency Anemia

It is logical that consuming too little iron will cause iron deficiency anemia but too lit-tle copper can also cause this problem. Iron and copper status are interrelated becausea copper-containing protein is needed for iron to be transported from the intestine.Even if iron intake is adequate, without copper, iron can’t get to tissues and this resultsin iron deficiency that may lead to anemia. Copper also functions in a number of im-portant proteins and enzymes that are involved in connective tissue synthesis, lipidmetabolism, maintenance of heart muscle, and function of the immune and centralnervous systems.21 Some of these roles are also reflected in the symptoms seen withcopper deficiency. When copper is deficient the protein collagen does not form nor-mally, so changes in the skeleton occur that are similar to those seen in vitamin C defi-ciency. Blood cholesterol levels are elevated in copper deficiency, reflecting copper’srole in cholesterol metabolism. Copper deficiency has also been associated with im-paired growth, degeneration of the heart muscle, degeneration of the nervous system,and changes in hair color and structure. Because copper is needed to maintain the im-mune system, a diet low in copper increases the incidence of infections. Copper is alsoan essential component of a form of the antioxidant enzyme superoxide dismutase(SOD), so a deficiency weakens antioxidant defenses.

Copper also interacts with zincThe zinc content of the diet can have a major impact on copper absorption. Whenzinc intake is high, it stimulates the synthesis of a zinc-binding protein. This proteinhelps regulate zinc absorption; but it also binds copper, preventing it from beingmoved out of mucosal cells into the blood.23 The antagonism between copper andzinc is so great that phytates, which inhibit zinc absorption, actually increase the ab-sorption and utilization of copper. Copper absorption is also reduced by high intakesof vitamin C, iron, manganese, and molybdenum.

Most Americans consume adequate amountsof copperThe RDA for copper for adults is 900 �g per day. We consume it in seafood, nuts andseeds, whole grain breads and cereals, and chocolate; the richest dietary sources ofcopper are organ meats such as liver and kidney (Figure 9.25). As with many othertrace elements, soil content affects the amount of copper in plant foods.

Severe copper deficiency is relatively rare, although it may occur in premature in-fants. Copper toxicity from dietary sources is also rare but has occurred as a result ofdrinking from contaminated water supplies or consuming acidic foods or beveragesstored in copper containers. Toxicity is more likely to occur from copper-containingsupplements. Excessive copper intake causes abdominal pain, vomiting, and diarrhea.The UL has been set at 10 mg of copper per day.

F I G U R E 9 . 2 5

These foods are good sources of copper.(Charles D. Winters)

Many body processes depend on zinc. It is involved in the functioning of nearly 100different enzymes. These enzymes are needed for the synthesis of DNA and RNA, themetabolism of carbohydrate, antioxidant protection, acid-base balance, and folate ab-sorption. Zinc also plays a role in the storage and release of insulin, the mobilizationof vitamin A from the liver, and the stabilization of cell membranes. Zinc is involvedin gene expression and therefore is needed for the growth and repair of tissues, the ac-tivity of the immune system, and the development of sex organs and bone. Zinc-containing proteins are needed for the activity of vitamin A, vitamin D, and a numberof hormones including the thyroid hormones, estrogen, and testosterone. Withoutzinc, these nutrients and hormones cannot bind to DNA to increase or decrease geneexpression and, hence, the synthesis of certain proteins.

A high phytate intake can cause zinc deficiencyThe essentiality of zinc in the human diet was not recognized until the 1960’s, when asyndrome of growth depression and delayed sexual development was seen in Iranianand Egyptian men consuming diets based on vegetable protein. Although the diet wasnot low in zinc, it was high in grains containing phytates, which interfered with zincabsorption, causing a deficiency.

In addition to poor growth and development, zinc deficiency causes skin rashes, diar-rhea, and impaired immune function. The impact of zinc deficiency on immune functionis rapid and extensive, causing a decrease in the number and function of immune cells inthe blood. The drop in immune function can lead to an increased incidence of infections.Diminished immune function is a concern even for moderate zinc deficiency. Because zincis needed for the proper functioning of vitamins A and D and the activity of numerous en-zymes, deficiency symptoms can resemble deficiencies of other essential nutrients. Zinc isalso needed for the thyroid hormones to function; a deficiency slows energy metabolism.

Symptomatic zinc deficiency is relatively uncommon in North America, but in devel-oping countries it has important health and developmental consequences. Supplementshave been shown to reduce the incidence of infections and diarrhea in children in devel-oping nations.24 The risk of zinc deficiency is greater in areas of the world where the dietis high in phytate, fiber, tannins, and oxalates, which limit zinc absorption. Groups atgreatest risk of deficiency worldwide are the elderly, low-income children, and vegetari-ans—particularly female vegans. Groups likely to be at risk of deficiency in the UnitedStates include young children, adolescent females, and older adults.25

Zinc in animal foods is better absorbed than that in plant foodsThe RDA for zinc is 11 mg per day for adult men and 8 mg per day for adult women.We consume it in red meat, liver, eggs, dairy products, vegetables, and some seafood(Figure 9.26). Whole grains are a good source, but refined grains are not because zincis lost in milling and not added back in enrichment. Because plant foods are high insubstances that bind zinc it is better absorbed from animal sources. Grain productsleavened with yeast provide more zinc than unleavened products because the yeastleavening of breads reduces the phytate content.

Zinc absorption and excretion are regulatedZinc consumed in the diet can be used by the cells lining the intestine, pass throughthese cells into the blood, or, in a manner analogous to iron, be trapped in the intestinalmucosal cells by a zinc-binding protein. When zinc intake is high more of this zinc-binding protein is made, so more zinc is held in the mucosal cells and lost into the gut

Zinc Is Needed for Enzyme, Hormone, and Vitamin Activity 315

Zinc Is Needed for Enzyme, Hormone, and Vitamin Activity


when these cells die (Figure 9.27). If zinc intake is low, less of this protein is made andmore dietary zinc passes into the blood. Unlike iron, excess zinc can be eliminated fromthe body. It is present in pancreatic and intestinal juices, which enter the lumen of theintestine during digestion. When zinc levels are low, the zinc that enters the gastroin-testinal tract from these sources is absorbed and recycled. When levels are high, it istrapped by the zinc-binding protein and eliminated in the feces when the cell dies.

Too much zinc can override regulatorymechanismsDespite the ability to regulate how much zinc is absorbed and eliminated from thebody, high intakes can override this regulation and lead to toxicity. A single dose of 1to 2 grams can cause gastrointestinal irritation, vomiting, loss of appetite, diarrhea,

Zinc (mg)

RDA

105


Lentils (1 c)Eggs (1)

Beef (3 oz)Crab (3 oz)




Kiwi (2 med)Apple (1 med)Broccoli (1 c)

Spinach, cooked (1 c)Potato, baked (1 med)



1 2 3 4 6 7 8 9 11 12

F I G U R E 9 . 2 6

Zinc content of selections from each group of the Food Guide Pyramid. The dashed line represents the RDA for adult men. As with iron, red meat is one of the bestsources of zinc. Other good sources include seafood and dairy products. (Rita Maas/The Image Bank/Getty Images)

Zinc is lostwhen celldies

Zinc-bindingprotein

Zinc-bindingprotein

Blood

Zinc

Zinc

Zn

Zinc

High Zinc Low Zinc

Zinc

NucleusNucleus

Zn

Zn Zn

ZnF I G U R E 9 . 2 7

Zinc absorption is regulated by a zinc-binding protein in intestinal mucosal cells.When zinc levels are high more of this protein is made, trapping more dietaryzinc and preventing it from being absorbed.

Selenium Provides Antioxidant Protection 317

abdominal cramps, and headaches. High intakes have been shown to decrease im-mune function and reduce concentrations of HDL cholesterol. Supplements provid-ing 50 mg per day of zinc have been shown to interfere with the absorption of copper.High doses of zinc can also interfere with iron absorption because zinc is also trans-ported by the iron transport protein transferrin. If zinc levels are high there is no roomfor iron to bind to transferrin. The converse is also true; too much iron can limit thetransport of zinc. A UL has been set at 40 mg per day from all sources based on theadverse effect of excess zinc on copper metabolism.21

Zinc is often marketed as a supplement to improve immune function, enhance fertilityand sexual performance, and cure the common cold. For individuals consuming adequatezinc, there is no evidence that extra is beneficial. But in individuals with a mild zinc defi-ciency, supplementation may result in improved wound healing, immunity, and appetite;in children it can result in improved growth and learning. In healthy older adults, supple-ments of zinc have been shown to improve the immune response (see Chapter 13).21

Zinc is added to throat lozengesto reduce cold symptoms. Thedirect contact between zinc andvirus-infected cells in the throatis hypothesized to reduceinflammation. However, there islittle experimental evidence tosupport the effectiveness of zinclozenges.

Selenium Provides Antioxidant Protection

When people think of antioxidants they usually think of vitamin C, vitamin E, andeven �-carotene, but selenium is also an antioxidant. It performs this role as part of anantioxidant enzyme called glutathione peroxidase. Selenium from the diet becomes apart of some of the amino acids that make up the final structure of this enzyme. Glu-tathione peroxidase neutralizes peroxides before they can form free radicals, whichcause oxidative damage. By reducing free radical formation, selenium can spare some ofthe requirement for vitamin E, because vitamin E is used to stop the action of free radi-cals once they are produced (Figure 9.28). In addition to its antioxidant role, seleniumis needed for the synthesis of the thyroid hormones, which regulate metabolic rate.

The selenium content of foods depends on where they are grownIn a region of China with very high selenium in the soil, people develop symptomssuch as hair loss and changes in their fingernails. While, in another part of China, aform of heart disease called Keshan disease occurs in part due to selenium deficiency.These geographic differences illustrate the wide variation in the amount of seleniumin the soil and how these differences affect selenium intake and human health. Sele-nium toxicity and deficiency are not likely to be a problem except when the diet is pri-marily made up of locally grown food. When the diet includes foods from manydifferent locations, the high selenium content of foods grown in one geographic re-gion is offset by the low selenium content of foods from other regions. The RDA forselenium for adults is 55 �g per day. The average intake in the United States meets ornearly meets this recommendation for all age groups. Seafood, kidney, liver, and eggsare excellent sources of selenium (Figure 9.29). Grains and seeds can be good sourcesdepending on the selenium content of the soil where they were grown. Fruits, vegeta-bles, and drinking water are generally poor sources.

Symptoms of selenium deficiency include muscular discomfort and weakness. Ke-shan disease occurs when selenium is deficient, but selenium deficiency is not the onlyfactor involved in this disease. It is believed to be due to a number of interactingthings, including selenium deficiency, other nutritional factors, and some type of in-fection. Selenium supplements relieve most of the symptoms of Keshan disease andreduce its incidence.

Selenium toxicity has been reported in the United States because of a manufactur-ing error that created mineral supplements containing a dose of 27 mg of seleniumper day. The individuals who used these supplements had symptoms that includednausea, diarrhea, abdominal pain, fingernail and hair changes, nervous system abnor-malities, fatigue, and irritability. Adverse effects such as hair and fingernail loss and

H2O2

H2O2

Glutathioneperoxidose(selenium)

Neutralizedperoxides

Vitamin E

Neutralizedfree radicals

Freeradicals

Cellulardamage

H2O2

H2O2

H2OPeroxides

F I G U R E 9 . 2 8

Selenium is a part of the enzyme glutathioneperoxidase, which neutralizes peroxides beforethey form free radicals. This can spare some ofthe need for vitamin E.

Glutathione peroxidase A selenium-containing enzyme that protects cells fromoxidative damage by neutralizing peroxides.

�*


gastrointestinal upset have been reported at much lower levels. The UL for adults is400 �g per day from diet and supplements.21

Selenium levels may affect cancerdevelopmentThe role of selenium in cancer has been under investigation for three decades. An in-creased incidence of cancer has been observed in regions where selenium intake islow. In 1996 a study investigating the effect of selenium supplements on people witha history of skin cancer found that the supplement had no effect on the recurrence ofskin cancer but the incidence of lung, prostate, and colon cancer all decreased in theselenium-supplemented group.26 There was a great deal of excitement about this result.Could selenium supplements reduce cancer risk? Many were hopeful, but continuedstudy has found that the results were not as miraculous as they originally seemed. Evi-dence now suggests that selenium supplements actually increase the incidence of certaintypes of skin cancer.27 The reduction in the incidence of lung and prostate cancer seen inthe 1996 study is believed to have occurred primarily in people who began with low lev-els of selenium. So, enough selenium is necessary to prevent cancer, but supplements ofselenium have not been shown to be of additional benefit in the general population.

Selenium (µg)

RDA

4010


Lentils (1 c)Eggs (1)

Beef (3 oz)Crab (3 oz)





Broccoli, cooked (1 c)Spinach, cooked (1 c)

Potato, baked (1 med)Oatmeal (1 c)

Spaghetti (1 c)White bread (2 sl)

Whole-wheat bread (2 sl)

503020 60

F I G U R E 9 . 2 9

Selenium content of selections from each group of the Food Guide Pyramid. The dashed line represents the RDA for adults. Seafood is rich in selenium and other animalproducts and plant foods are also good sources. (PhotoDisc, Inc./Getty Images)

Iodine Is Needed to Synthesize Thyroid Hormones

More than half of the iodine in your body is stored in a small gland in your neckcalled the thyroid gland. The reason iodine is concentrated in this gland is that it is anessential component of the thyroid hormones. Thyroid hormones regulate metabolicrate, growth, and development, and promote protein synthesis. If blood levels of the

Iodine Is Needed to Synthesize Thyroid Hormones 319

thyroid hormones drop, thyroid-stimulating hormone is released. This hormone sig-nals the thyroid gland to take up iodine and synthesize more thyroid hormones.When the supply of iodine is adequate, thyroid hormones can be made and their pres-ence turns off the synthesis of thyroid-stimulating hormone.

Iodine deficiency causes goiter and affectsgrowth and developmentIf iodine is deficient, thyroid hormones cannot be made. Without sufficient thyroidhormones metabolic rate slows, causing fatigue and weight gain. The most obviousoutward sign of deficiency is an enlarged thyroid gland called a goiter (Figure 9.30). Agoiter forms when reduced thyroid hormone levels cause thyroid-stimulating hor-mone to be released, stimulating the thyroid gland to make more thyroid hormones.Because iodine is unavailable, the hormones cannot be made, but the stimulation con-tinues causing the thyroid gland to enlarge. In milder cases of goiter, treatment withiodine causes the thyroid gland to return to normal size, but it may remain enlarged inmore severe cases.

Thyroid hormone is needed for growth, development, and protein synthesis, so io-dine deficiency causes other problems in addition to goiter. If iodine is deficient dur-ing pregnancy, it increases the risk of stillbirth and spontaneous abortion. Deficiencyalso can cause a condition called cretinism in the offspring. Cretinism is characterizedby symptoms that include mental retardation, deaf mutism, and growth failure. Io-dine deficiency during childhood and adolescence can result in goiter and impairedmental function.

Iodine deficiency was common in the central United States and Canada in the early1900’s, but today it is rare in this part of the world due to the addition of iodine totable salt. Iodized salt was first used in Switzerland in the 1920’s as a way to combatiodine deficiency. Salt iodinization and other forms of iodine supplementation, suchas injections or oral doses of iodized oil, are now used in most countries with an io-dine deficiency disease problem of public health significance. Despite these efforts io-dine deficiency remains a world health problem. Worldwide, 600 million people havegoiter and 1.5 billion people are at risk for iodine deficiency.28

Iodine comes from the sea and is added to our saltThe iodine content of foods varies depending on the soil where plants are grown orwhere animals graze. Iodine is found in sea water so seafood and plants grown nearthe sea are high in iodine. Plants grown inland have lesser amounts, depending on theiodine content of the soil. In some plant foods substances called goitrogens increasethe risk of iodine deficiency by interfering with the utilization of iodine or with thy-roid function. Goitrogens are found in turnips, rutabaga, cabbage, cassava, and millet.When these foods are boiled, the goitrogen content is reduced because some of thesecompounds leach into the cooking water. They are primarily a problem in Africancountries where cassava is a dietary staple. In the American diet goitrogens are not aproblem because they are present in foods that are not consumed to any large extentin the typical diet.

Since the iodinization of salt began in the early 1900’s, the typical iodine intake inNorth America has met or exceeded the RDA of 150 �g per day for adult men andwomen. Iodized salt is commonplace in the United States, and only iodized salt is soldin Canada. It takes only about half a teaspoon of iodized salt to meet recommenda-tions. We also get iodine from contaminants and other additives in foods. Iodine-containing additives used in cattle feed and disinfectants used on milking machinesand storage tanks increase the iodine content of dairy products. Iodine-containingsterilizing agents are also used in fast-food restaurants, and iodine is used in doughconditioners and some food colorings.

Despite our intake of iodine from iodized salt and contaminants, toxicity is rare.Chronically high intakes of iodine can cause an enlargement of the thyroid gland

F I G U R E 9 . 3 0

Iodine deficiency causes enlargement of thethyroid gland, a condition called goiter. (AlisonWright/Corbis)

Although the seas provide much ofour iodine, sea salt is a poor sourcebecause the iodine is lost in thedrying process.

Goiter An enlargement of the thyroidgland caused by a deficiency of iodine.�*

Cretinism A condition resulting frompoor maternal iodine intake during pregnancythat causes stunted growth and poormental development in offspring.

�*


Your Choice: Should You BuyIodized?

When selecting a box of salt for the kitchen cupboard, youcan choose one that just says “salt” or one that is labeled“iodized salt.” Iodized salt is salt to which the trace elementiodine has been added. Which should you choose?

You can get enough iodine without using iodized salt.But some of your food needs to come from the ocean or aplace that has lots of iodine in the soil. When the earth wasformed, all soils were high in iodine, but today iodine ismost plentiful in areas close to the sea. The soil inmountainous areas and river valleys has little iodine leftbecause it has been washed out by glaciers, snow, rain, andflood waters. The iodine washed from the soil hasaccumulated in the oceans, where it is present as iodideions. When these ions come in contact with sunlight, theyare oxidized to form iodine, which can escape into the air.Every year approximately 400,000 tons of iodine escapesinto the atmosphere from the ocean surface. The iodine inthe atmosphere is returned to the soil in rain, but the returnis slow and the amounts returned to the soil are small. Inareas where the forces of nature have resulted in iodine-deficient soil, the iodine deposited from rain will be washedaway again by these same forces. Therefore, iodine-deficient soil will remain deficient.

The effects of iodine-depleted soil on human health havebecome a part of history in many areas of the world. InEurope the presence of iodine deficiency was recorded inclassical art, which portrayed even the wealthy with goiterand cretinism. Leonardo da Vinci is said to have been moreknowledgeable about goiter than medical professors of histime.1 A century ago goiter was endemic in the centralregions of North America. However, the iodinization of salt,which began in the early 20th century, has virtuallyeliminated iodine deficiency in the United States,

Switzerland, andsome other Europeancountries.

Why fortify salt?Salt was selected asthe vehicle for addediodine because it is afood item consistentlyconsumed by themajority of thepopulation at risk.People do not need

to change their eating habits to include the fortifiedproduct in their diet. The iodine can be added to saltuniformly, inexpensively, and in a form that is well utilizedby the body. It can be added in amounts that eliminatedeficiency when typical quantities of salt are consumed bythe population, but is unlikely to be consumed in toxicamounts. Developing nations, where iodine deficiency is stilla public health problem, have experimented with iodizedsalt as well as the fortification of other foods that arefrequently consumed such as fish sauce, sugar, and drinkingwater.2

So, should you choose iodized salt? For about 50 yearsthe average intake of iodine in the United States hasexceeded the RDA, and iodine deficiency has been rare.3 Thetypical diet includes iodine from iodized salt as well as fromfoods transported across the country and around the world.However, recent surveys have shown a significant reductionin the average American iodine intake.4 The average intakeis still considered sufficient, but the drop has increased thenumber of people who are at risk of deficiency. There aremany factors that may have contributed to the decrease iniodine intake.4 Egg yolks are rich in iodine, but eggconsumption has declined due to concerns about dietarycholesterol intake. The amount of salt added in the homemay also have declined due to recommendations regardingblood pressure. And, most of the salt in the American dietcomes from processed foods, which contain non-iodizedsalt. There have also been changes in the amounts of iodine-containing additives and contaminants in foods. Despite thisdecrease, most people get plenty of iodine, especially if theylive near the coast or buy food in a supermarket. However, ifyou eat little seafood, live inland where the soil is deficientin iodine, and consume primarily foods grown locally,choosing salt labeled “iodized” may be the best way toensure your iodine needs are met.

References1. Underwood, B. A. Micronutrient malnutrition: Is it being eliminated? Nutr.

Today 33:121–129, 1998.2. World Health Organization. Eliminating iodine deficiency disorders. Available

online at www.who.int/nut/idd.htm/Accessed August 23, 2004.3. Hollowell, J. G., Staehling, N. W., Hannon, W. H., et al. Iodine nutrition in the

United States. Trends and public health implications: Iodine excretion datafrom National Health and Nutrition Examination Surveys I and III (1971–1974and 1988–1994). J. Clin. Endocrinol. Metab. 83:3401–3408, 1998.

4. Lee, K., Bradley, R., Dwyer, J., and Lee, S. L. Too much versus too little: Theimplications of current iodine intake in the United States. Nutr. Rev.57:177–181, 1999.(George Semple)

that resembles goiter. The UL for adults is 1100 �g of iodine per day from allsources. Goiter from excessive iodine can also occur if iodine intake changes drasti-cally. For example, in someone with a marginal intake, a large dose from supple-ments could cause thyroid enlargement even at levels that would not be toxic in ahealthy person.

Chromium Helps Regulate Blood Sugar 321

Chromium Helps Regulate Blood Sugar

Glucose fuels your cells, but you can’t use this energy unless the glucose gets intoyour cells where the reactions that synthesize ATP occur. Getting glucose into cellsrequires the hormone insulin, and chromium helps insulin to do its job. When car-bohydrate is consumed, insulin is released and binds to receptors on cell mem-branes. The binding of insulin triggers the uptake of glucose by cells, therebyreducing blood sugar levels. It also stimulates protein and fat synthesis. Chromiumis part of a small peptide that stabilizes the bound insulin and increases its effects.29

When chromium is deficient, it takes more insulin to keep blood glucose levelsnormal.

A deficiency of chromium affects the ability to regulate blood glucose, causing diabetes-like symptoms, such as elevated blood glucose levels and increased insulinlevels. There is some evidence that chromium deficiency may play a role in the devel-opment of type 2 diabetes, but its role is not clear. Chromium deficiency may alsocause elevated blood cholesterol and triglyceride levels, but the role of chromium inlipid metabolism is not fully understood.30 Overt chromium deficiency is not a prob-lem in the United States.

Chromium supplements do not help build musclesSome people take supplements of a form of chromium called chromium picolinate.These supplements are promoted to reduce body fat and increase muscle mass, re-sults that appeal to individuals wanting to lose weight as well as to athletes tryingto build muscle (Figure 9.31). Because chromium is needed for insulin action andinsulin promotes protein synthesis, it is likely that adequate chromium is necessaryto increase lean body mass. However, studies on the effects of chromium picolinateor other chromium supplements in healthy human subjects have found no benefi-cial effects on muscle strength, body composition, weight loss, or other aspects ofhealth.31

Toxicity is always a concern when nutrients are included in popular supple-ments. There have been reports that have linked chromium supplements to kidneydamage and changes in DNA. However, the evidence that chromium was the causeof the kidney damage was not strong and the DNA damage only occurred in testtubes, not in people. There is little evidence of dietary toxicity in humans and theDRI committee concluded that there was insufficient data to establish a UL forchromium.

Refined foods are low in chromiumThe recommended intake for chromium is 35 �g per day for men and 25 �g per dayfor women. Dietary sources of chromium include liver, brewer’s yeast, nuts, and wholegrains. Milk, vegetables, and fruit are poor sources. Refined carbohydrates such aswhite breads, pasta, and white rice are also poor sources because chromium is lost inmilling and not added back in the enrichment process. Chromium intake can be in-creased by cooking in stainless steel cookware because chromium leaches from thesteel into the food.

F I G U R E 9 . 3 1

Chromium supplements are marketed toincrease lean body mass and decrease bodyfat. (George Semple)


Does the water in your community contain fluoride? Fluoride is added to drinkingwater to reduce the incidence of dental caries (cavities). Fluoride protects teeth in anumber of ways. During tooth formation, it is incorporated into the crystals of thetooth enamel. These fluoride-containing crystals are more resistant to acid than thoseformed when fluoride is absent. The fluoride-containing crystals help protect the teethfrom the cavity-causing acids produced by bacteria in the mouth. Fluoride has itsgreatest effect on dental caries prevention up to the age of 13, the period of maximumtooth development, but it has been shown to also have benefits in adults. In additionto making tooth enamel more acid-resistant, fluoride in saliva reduces cavities by re-ducing acid produced by bacteria, inhibiting the dissolution of tooth enamel by acid,and increasing enamel re-mineralization after acid exposure.

Fluoride is also incorporated into the mineral crystals in bone. There is evidencethat fluoride stimulates new bone formation and has therefore been suggested tostrengthen bones in adults with osteoporosis. Slow-release fluoride supplements havebeen shown to increase bone mass and prevent new fractures.32

Too much fluoride causes tooth discolorationDid you ever read your toothpaste tube? Somewhere on the label it will warn: “If you ac-cidentally swallow more than used for brushing, seek professional help or contact a poi-son control center immediately.” The fluoride in toothpaste is good for your teeth, butswallowing too much can cause problems. Due to concern over excess fluoride intake,this warning is now required on all fluoride-containing toothpastes. In children toomuch fluoride causes mottled teeth, a condition called fluorosis (Figure 9.32). A recentincrease in fluorosis in the United States has occurred due to the chronic ingestion oftoothpaste containing fluoride. In adults doses of 20 to 80 mg per day can result inchanges in bone health that can be crippling, as well as changes in kidney function andpossibly nerve and muscle function. Death was reported with an intake of 5 to 10 gramsper day. The UL for fluoride is set at 0.1 mg per kg per day for infants and children lessthan 9 years of age, and at 10 mg per day for those between the ages of 9 and 70.14

Some people believe that water fluoridation represents a public health hazard andthat the added fluoride increases the risk of cancer. These beliefs are not supported byscientific facts; the small amounts consumed in drinking water do not pose a risk forhealth problems such as cancer, kidney failure, or bone disease.

Most of our fluoride comes from water and toothpasteFluoride is present in small amounts in almost all soil, water, plants, and animals. Therichest dietary sources of fluoride are fluoridated water, tea, and marine fish consumedwith their bones. Tea contributes significantly to total fluoride intake in countries thatconsume large amounts of the beverage.14 In the United States, most of the fluoride inthe diet comes from toothpaste and from fluoride added to the water supply—usually0.7 to 1.2 mg per liter. (Water companies often report fluoride levels in parts per mil-lion [ppm], 1 mg per liter � 1 ppm.) Swallowed toothpaste is estimated to contribute

Fluoride Prevents Cavities

The fluoridation of public drinkingwater to prevent dental cariesbegan in Grand Rapids, Michigan in1945. Today over half of us live inareas where fluoride is added to thewater or it is naturally present inour water in adequate amounts.

Fluorosis Mottling of the toothenamel caused by chronic over-consumption of fluoride.

�*

The recognition of the importanceof fluoride in dental health wasmade in the 1930’s when it wasnoted that children with fluorosishad fewer dental caries. It wassoon recognized that loweramounts of fluoride could protectagainst cavities without causingmottled teeth.

F I G U R E 9 . 3 2

Too much dietary fluoride causes the teeth to appear mottled(enamel fluorosis). (a) Normal teeth. (b) Teeth showing enamelfluorosis. (a: E. H. Gill/Custom Medical Stock Photo, Inc.; b: NIH/Custom Medical Stock Photo, Inc.)

For more information on fluoride and dental caries, go to the American

Dental Association Oral Health Topics at

www.ada.org/public/topics

(a) (b)

about 0.6 mg per day of fluoride in young children. Because food readily absorbs thefluoride in cooking water, the fluoride content of food can be significantly increasedwhen it is handled and prepared using fluoridated water. Cooking utensils also affectfood fluoride content. Foods cooked with Teflon utensils can pick up fluoride fromthe Teflon, whereas aluminum cookware can decrease fluoride content. Fluoride is ab-sorbed into the body in proportion to its content in the diet.

The AI for fluoride from all sources is based on a recommended intake of 0.05 mgper kg per day for everyone 6 months of age and older. This is equivalent to about 3.8mg per day for men based on a weight of 76 kg and for women it is equivalent to 3.1mg per day based on a weight of 61 kg. The American Academy of Pediatrics suggestsa fluoride supplement of 0.25 mg per day for children 6 months to 3 years of age, 0.5mg per day for children ages 3 to 6 years, and 1.0 mg per day for those ages 6 to 16who are receiving less than 0.3 mg per liter of fluoride in the water supply. These sup-plements are available by prescription for children living in areas with low water fluo-ride concentrations.

Sulfur, Manganese, Molybdenum, and Other Minerals Are Also Essential 323

Do you drink bottled water? If theanswer is yes, you might beincreasing your risk of tooth decay.Bottled water does not containfluoride and dentists are becomingconcerned that the increasingpopularity of bottled water isreducing typical fluoride intake andincreasing the risk of dental caries.

Sulfur, Manganese, Molybdenum, and Other Minerals Are Also Essential

There are many other minerals in the human body. Some of these may be essential forhuman health, and others may be present only as a result of environmental exposure.DRI recommendations have been set for manganese and molybdenum.

Manganese participates in enzymatic reactionsManganese is a mineral that is often confused with magnesium. Although it is in-volved in some of the same processes, it is needed in far smaller amounts. The AI is2.3 mg per day for men and 1.8 mg per day for women based on the amounts con-sumed in the healthy population.

Manganese is a constituent of some enzymes and an activator of others. Manganese-requiring enzymes are involved in amino acid, carbohydrate, and cholesterol metab-olism; bone formation; urea synthesis; and antioxidant protection as a componentof superoxide dismutase.

The best dietary sources of manganese are whole grains, nuts, legumes, and leafygreen vegetables (Figure 9.33). A naturally occurring manganese deficiency has neverbeen reported in humans. Manganese deficiency in animals causes growth retardation,reproductive problems, birth defects in the offspring, and abnormalities in brain func-tion, bone formation, glucose regulation, and lipid metabolism. Toxic levels of man-ganese result in damage to the nervous system. The UL is 11 mg per day from allsources.

Molybdenum activates enzymesLike many other trace elements, molybdenum is needed to activate enzymes. It func-tions in the metabolism of sulfur-containing amino acids and nitrogen-containingcompounds present in DNA and RNA, the production of uric acid, and the oxidationand detoxification of various other compounds. The molybdenum content of foodvaries with the molybdenum content of the soil where the food is produced. The mostreliable sources include milk, milk products, organ meats, breads, cereals, and legumes.Molybdenum is readily absorbed from foods; the amount in the body is regulated byexcretion in the urine and bile.

An RDA for molybdenum has been set at 45 �g per day for adults. A naturally oc-curring deficiency has never been reported. Although there are few data on adverse ef-fects of high intakes of molybdenum in humans, a UL of 2000 �g per day was setbased on impaired growth and reproduction in animals.

F I G U R E 9 . 3 3

Legumes, nuts, and whole grains are high inmanganese. (Rita Maas/The Image Bank/Getty Images)


Sulfur is a part of proteins and other moleculesSulfur is one of the major minerals; over 100 mg is present in our bodies. Sulfur isfound in sulfur-containing amino acids in proteins, the sulfur-containing vitamins,and a few other molecules. The sulfur-containing amino acids methionine and cys-teine are needed for protein synthesis. Cysteine is also part of the compound glu-tathione, which is important in detoxifying drugs and protecting cells from oxidativedamage. Thiamin and biotin are sulfur-containing vitamins that are essential for en-ergy production. We consume sulfur in proteins and in food preservatives such as sul-fur dioxide, sodium sulfite, and sodium and potassium bisulfite, which are used asantioxidants. There is no recommended intake for sulfur, and no deficiencies areknown when protein needs are met (see Table 9.1).

Other minerals may be important for healthThere is evidence that arsenic, boron, nickel, silicon, and vanadium play a role inhuman health. The need for and functions of these minerals have been reviewed bythe DRI committee but there was not sufficient data to establish a recommended in-take for any of these elements. ULs have been set for boron, nickel, and vanadium.Other trace elements that play a physiological role include aluminum, bromine, cad-mium, germanium, lead, lithium, rubidium, and tin. The specific functions of thesehave not been defined, and they have not been evaluated by the DRI committee. Allthe minerals, both those known to be essential and those that are still being assessedfor their role in human health, can be obtained by choosing a variety of foods fromeach of the groups of the Food Guide Pyramid.


To add more high iron foods• Eat red meat, poultry, or fish—they are all good sources of heme iron• Add raisins to your oatmeal• Have a fortified breakfast by eating iron-fortified cereal• Dust off the iron skillet• Have some beans—they are a good vegetarian source of iron

To increase your iron absorption• Have orange juice with your iron-fortified cereal• Don’t take your calcium supplement with your iron sources

Think zinc• Scramble some eggs• Beef up your zinc by having a few ounces of meat• Eat whole grains but make sure they are yeast leavened

Trace down your minerals• Check to see if your water is fluoridated• See if your salt is iodized• Replace refined grains with whole grains to increase your chromium intake• Have some seafood to add selenium to your diet

S U M M A R Y

Summary 325

T H I N K I N G F O R Y O U R S E L F

1. How does your diet compare to the DASH diet?a. Use 1 day of the food record you kept in Chapter 2 to

compare the number of servings you ate from each ofthe food groups to the number of servingsrecommended by the DASH diet for your energyintake as shown in Table 9.3.

b. Suggest modifications to your diet that would allow itto meet DASH guidelines.

c. What difficulties or inconveniences do you see withfollowing this dietary pattern?

d. What other dietary or lifestyle changes might youmake if you are at high risk of hypertension?

2. Do you drink enough fluid?a. Keep a log of all the fluids you consume in 1 day.

Calculate your fluid intake by totaling the volume ofwater, beverages, and foods that are liquid at roomtemperature.

b. How does your intake on this day compare withyour estimated requirement? How about if youadded an hour of jogging or basketball to your day?

3. How much sodium do processed foods add to yourdiet?a. Use food labels to estimate the amount of sodium you

consume from processed foods each day.

b. Make a list of processed foods you commonly eat thatcontain more than 10% of the Daily Value for sodiumper serving.

c. What less-processed choices could you substitute forthese?

4. Do you get enough calcium?a. Using the food record you kept in Chapter 2, calculate

your average calcium intake.b. How does your intake compare with the AI for

calcium for someone of your age and sex?c. If your calcium intake is below the AI, modify your

diet to increase your calcium consumption withoutsignificantly increasing your energy intake.

5. Are you at risk for iron deficiency?a. Using the 3-day food intake record you kept in

Chapter 2, calculate your average daily intake of iron.b. How does your iron intake compare with the

recommendation for someone of your age and sex?c. If your intake is low, suggest modifications to your diet

to meet the RDA for iron for someone your age and sex.d. If your diet already meets the recommendations for

iron, make a list of foods you like that are goodsources of iron.

e. Identify the major food sources of iron in your currentdiet and indicate whether they contribute heme iron.

1. Minerals are elements needed by the body to regulatechemical reactions and provide structure. Theirbioavailability is affected by their food sources, thebody’s need, and interactions with other minerals,vitamins, and other dietary components such as fiber,phytates, oxylates, and tannins.

2. Water is an essential nutrient that accounts for about60% of adult body weight. Since water isn’t stored inthe body, intake from water, other fluids, and foodsmust replace losses in urine, feces, and sweat, and fromevaporation. Water provides transport, protection,lubrication, and temperature regulation in the body.Water balance is controlled by stimulating intake withthirst and regulating the amount lost in the urine. Therecommended intake of water is 2.7 liters per day forwomen and 3.7 liters per day for men; needs varydepending on environmental conditions and activitylevel. Dehydration can occur if water intake is too lowor output is excessive.

3. The minerals sodium, chloride, and potassium areelectrolytes important in the maintenance of fluidbalance and the functioning of nerves and muscles. The North American diet is abundant in sodium and chloride from processed foods and table salt but generally low in potassium, which is high inunprocessed foods such as fresh fruits and vegetables.Recommendations for health suggest that we should eat more potassium and less salt.

4. Electrolyte and fluid balance is regulated primarily bythe kidneys. Failure of these regulatory mechanismsmay be a cause of hypertension. Diet affects the risk of hypertension: a high sodium intake increases risk; a low potassium, magnesium, and calcium intake alsoincreases risk.

5. Bone is a living tissue that is constantly being brokendown and reformed. Peak bone mass occurs in youngadulthood. As adults age more bone is broken downthan is made, causing a decrease in overall bone mass.


11. Zinc is needed for the activity of many enzymes, andzinc-containing proteins are needed for the activity ofvitamins A and D and a number of hormones. Zincabsorption is regulated by a protein that binds zinc in themucosal cells and limits how much can enter the blood.High levels of phytate interfere with zinc absorption.Zinc deficiency depresses immunity but too much canhave the same effect; zinc deficiency also contributes tocopper and iron deficiency. Good sources of zinc includered meats, eggs, dairy products, and whole grains.

12. Selenium is part of the enzyme glutathione peroxidase,which protects against oxidative damage by preventing freeradical formation. Adequate dietary selenium spares someof the need for vitamin E. Dietary sources include seafood,eggs, organ meats, and plant foods grown in selenium-richsoils. In China, selenium deficiency is associated with aheart condition known as Keshan disease. Low seleniumintake has been linked to increased cancer risk.

13. Iodine is an essential component of thyroid hormones,which control basal metabolic rate, growth, anddevelopment. When iodine is deficient, the thyroidgland enlarges, forming a goiter. Iodine deficiency alsoaffects growth and development. The use of iodized salthas virtually eliminated iodine deficiency in NorthAmerica, but it remains a world health problem. Thebest sources of iodine in the diet are seafood, foodsgrown near the sea, and iodized salt.

14. Chromium is needed for normal insulin action andglucose utilization. It is found in liver, brewer’s yeast,nuts, and whole grains.

15. Fluoride is necessary for the maintenance of bones andteeth and prevention of dental caries. Most of thefluoride in the diet in the United States comes fromfluoridated drinking water and toothpaste.

16. Manganese and molybdenum are both cofactors neededfor the activity of a number of enzymes. Sulfur is amajor mineral found in sulfur-containing amino acids,the sulfur-containing vitamins, and a few othermolecules; it is part of a buffer that helps regulate acid-base balance. Boron, arsenic, nickel, silicon, andvanadium may be essential in small amounts but can betoxic if consumed in excess.

This bone loss is accelerated in women for about 5 yearsafter menopause. A low bone mass causes osteoporosis,a condition that increases the risk of bone fractures.

6. Most of the calcium in the body is found in bone, butcalcium is also essential for nerve transmission, musclecontraction, blood clotting, and blood pressureregulation. Blood levels of calcium are tightly regulatedby the hormones PTH and calcitonin, which affect theamount of calcium excreted in the urine, absorbed fromthe diet, and released from bone. Good sources ofcalcium in the American diet include dairy products,fish consumed with bones, and leafy green vegetables.

7. Phosphorus is widely distributed in foods. It has animportant structural role in bones and teeth.Phosphorus is also part of a buffer system that helpsprevent changes in acidity and is an essentialcomponent of phospholipids, ATP, and DNA.

8. Magnesium is important for bone health and it isneeded as a cofactor for numerous reactions throughoutthe body as well as to stabilize ATP. It is important forblood pressure regulation and is essential for nerve andmuscle conductivity. The best dietary sources are wholegrains and green vegetables.

9. Iron functions as part of hemoglobin, which transportsoxygen in the blood. Iron deficiency anemia is the mostcommon nutritional deficiency worldwide. The amountof iron absorbed depends on other foods in the diet aswell as the type of iron. Heme iron, found in meats, ismore absorbable than nonheme iron, found in meatand plant foods. If iron stores are low, more iron istransported from the intestinal cells to body cells. Whenbody stores are adequate, less iron is transported. If toomuch iron is absorbed, the heart and liver can bedamaged and diabetes and cancer are more likely. Asingle large dose of iron is toxic and can be fatal.

10. Copper functions in a number of proteins that affect ironand lipid metabolism, synthesis of connective tissue, andantioxidant protection. A copper-containing protein isneeded for iron transport. High levels of zinc can cause acopper deficiency. A copper deficiency can result inanemia and bone abnormalities. Seafood, nuts, seeds, andwhole grain breads and cereals are good sources of copper.

R E V I E W Q U E S T I O N S

1. How is the amount of water in the body regulated?2. Describe the functions of water in the body.3. List three factors that increase water needs.4. What is the role of the electrolytes (sodium, potassium,

and chloride) in the body?5. What types of foods contribute the most sodium to the

North American diet?6. What types of foods are good sources of potassium?7. What is the DASH diet, and how does it affect blood

pressure?

8. What is the major source of calcium in the NorthAmerican diet?

9. When blood calcium levels drop too low, how does thebody return levels to normal?

10. Why might low calcium intake during childhoodincrease the risk of osteoporosis?

11. Why are women more likely than men to developosteoporosis?

12. Name four structures or molecules that containphosphorus.

13. What is the function of magnesium in the body?14. Why does iron deficiency cause red blood cells to be

small and pale?15. List several good sources of iron in the diet and indicate

if they contain heme iron.16. Discuss three factors that affect iron absorption.17. What is hemochromatosis?18. Explain why a deficiency of copper can contribute to

anemia.

19. How does zinc affect the synthesis of proteins?20. Why does excess zinc cause a deficiency of copper?21. What is the role of selenium in the body?22. What is a goiter and what causes it?23. What is the role of chromium in the body?24. How does fluoride function in dental health?

References 327

R E F E R E N C E S

1. Askew, E.W. Nutrition and performance in hot, cold, and high-altitude environments. In Nutrition in Exercise and Sport, 3rd ed.Wolinsky, I., ed. Boca Raton, Fla: CRC Press, 1998: 597–619.

2. Shen, H-P. Body fluids and water balance. In Biochemical andPhysiological Aspects of Human Nutrition. Stipanuk, M. ed.Philadelphia: W. B. Saunders, 2000: 843–865.

3. Institute of Medicine, Food and Nutrition Board. DietaryReference Intakes for Water, Salt and Potassium. Washington, DC:National Academy Press, 2004.

4. Oppliger, R. A., Case, H. S., Horswill, C. A., et al. AmericanCollege of Sports Medicine position statement: Weight loss inwrestlers. Med. Sci. Sports Exerc. 28:ix–xii, 1996.

5. Chobanian, A. V., Bakris, G. L., Black, H. R., et al. Seventhreport of the Joint National Committee on Prevention,Detection, Evaluation, and Treatment of High Blood Pressure.Joint National Committee on Prevention, Detection, Evaluation,and Treatment of High Blood Pressure. National Heart, Lung,and Blood Institute. Hypertension 42:1206–1252, 2003.

6. American Heart Association. Factors that contribute to highblood pressure. Available online at www.americanheart.org/presenter.jhtml?identifier-4650/Accessed August 31, 2004.

7. Sacks, F. M., Svetkey, L. P., Vollmer, W. M., et al. Effects on bloodpressure of reduced dietary sodium and the Dietary Approaches toStop Hypertension (DASH) diet. DASH-Sodium CollaborativeResearch Group. N. Engl. J. Med. 344:3–10, 2001.

8. Jee, S. H., Miller, E. R., 3rd, Guallar, E., et al. The effect ofmagnesium supplementation on blood pressure: A meta-analysisof randomized clinical trials. Am. J. Hypertens. 15:691–696,2002.

9. Allender, P. S., Cutler, J. A., Follmann, D., et al. Dietary calciumand blood pressure: A meta-analysis of randomized clinical trials.Ann. Intern. Med. 124:825–831, 1996.

10. Greenland, P. Beating high blood pressure with low sodiumDASH. N. Engl. J. Med. 344:53–55, 2001.

11. National Institutes of Health. Consensus Development ConferenceStatement: Osteoporosis Prevention, Diagnosis, and Therapy, March27–29, 2000. Available online at consensus.nih.gov/cons/111/111_statement.htm/Accessed August 31, 2004.

12. Osteoporosis overview. Osteoporosis and related bone diseases.National Resource Center. Available online atwww.osteo.org/osteo.html/Accessed August 23, 2004.

13. Bohannon, A. D. Osteoporosis and African American women. J. Womens Health Gend. Based Med. 8:609–615, 1999.

14. Institute of Medicine, Food and Nutrition Board. DietaryReference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D,and Fluoride. Washington, DC: National Academy Press, 1997.

15. Heaney, R. P., Weaver, C. M., and Recker, R. R. Calciumabsorption from spinach. Am. J. Clin. Nutr. 47:707–709, 1988.

16. Bronner, F., and Pansu, D. Nutritional aspects of calciumabsorption. J. Nutr. 129:9–12, 1999.

17. Riggs, B. L., O’Fallon, W. M., Muhs, J., et al. Long-term effectsof calcium supplementation on serum parathyroid hormone level,bone turnover, and bone loss in elderly women. J. Bone Miner.Res. 13:168–174, 1998.

18. Sojka, J. E., and Weaver, C. M. Magnesium supplementation andosteoporosis. Nutr. Rev. 53:71–74, 1995.

19. Centers for Disease Control and Prevention. Recommendationsto prevent and control iron deficiency in the United States. Morb. Mortal. Wkly. Rep. 47:1–29, 1998. Available online atwww.cdc.gov/mmwr/preview/mmwrhtml/00051880.htm/Accessed August 23, 2004.

20. World Health Organization. Micronutrient deficiencies, battlingiron deficiency anemia. The challenge, updated September 3,2003. Available online at www.who.int/nut/ida.htm/AccessedAugust 23, 2004.

21. Food and Nutrition Board, Institute of Medicine. Dietary ReferenceIntakes: Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper,Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium,and Zinc. Washington, DC: National Academy Press, 2001.

22. Iron-containing supplements and drugs: Label warning statementsand unit-dose packaging requirements. Federal Register, January 1997.

23. Turnlund, J. R. Copper. In Modern Nutrition in Health andDisease, 9th ed. Shils, M. E., Olson, J. A., Shike, M., and Ross, A. C., eds. Baltimore: Williams & Wilkins, 1999: 241–252.

24. Fraker, P. J., King, L. E., Laakko, T., and Vollmer, T. L. Thedynamic link between the integrity of the immune system andzinc status. J. Nutr. 130:1399S–1406S, 2000.

25. Briefel, R. R., Bialostosky, K., Kennedy-Stephenson, J., et al. Zincintake of the U.S. population: Findings from the Third NationalHealth and Nutrition Examination Survey, 1988–1994. J. Nutr.130:1367S–1373S, 2000.

26. Clark, L. C., Combs, G. F., Jr., Turnbull, B. W., et al. Effect ofselenium supplementation for cancer prevention in patients withcarcinoma of the skin. JAMA 276:1957–1968, 1996.

27. Duffield-Lillico, A. J., Slate, E. H., Reid, M. E., et. al. Seleniumsupplementation and secondary prevention of nonmelanoma skincancer in a randomized trial. J. Natl. Cancer Inst. 95:1477–1481,2003.

28. World Health Organization. Eliminating iodine deficiencydisorders. Available online at www.who.int/nut/idd.htm/AccessedAugust 23, 2004.

29. Vincent, J. B. The biochemistry of chromium. J. Nutr.130:715–718, 2000.

30. Anderson, R. A. Chromium as an essential nutrient for humans.Regul. Toxicol. Pharmacol. 26:S35–S41, 1997.

31. Lukaski, H. C. Chromium as a supplement. Ann. Rev. Nutr.19:279–301, 1999.

32. Pak, C. Y., Sakhaec, K., and Zerwekh, J. E. Sustained-releasesodium fluoride in the management of established menopausalosteoporosis. Am. J. Med. Sci. 313:23–32, 1997.

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