Contemporary Nutrition 6th ed.

Chapter 8, Vitamins

Vitamins• Essential organic substances• Produce deficiency symptoms when

missing from diet • Yield no energy (kcals)• Basic functions

– Facilitate energy-yielding chemical reactions– Function as co-enzymes

Coenzymes

Fig. 06.11

Vitamins

• 13 known specific nutrients• Involved in almost every metabolic

process• Minute amounts needed (micronutrients)• Body cannot make (indispensible)• Fat soluble• Water soluble

Vitamins

• Named in order of discovery• Megadose (>10x needs) to correct

deficiency– Vitamin C – scurvy– Vitamin D – psoriasis

• Synthetic vs food sources– Vitamin E – natural form– Folic acid – synthetic form

• All vitamins thought to be discovered

Preservation of Vitamins

• Decreased vitamin content– Improper storage– Excessive cooking– Exposure to light, heat, air, water, and alkalinity

• Eat foods soon after harvest• Freeze foods not consumed within a few

days• Blanching destroys enzymes

– Slows down vitamin degradation

Fat-Soluble Vitamins Overview

• Dissolve in organic solvents• Not readily excreted; toxicity• Absorbed with fat

– Problem if fat malabsorption present• Transported like fat in chylomicrons

– (40-90% absorbed)

Vitamin A

• First vitamin discovered• Reported as essential in 1913• Egyptians and Greeks understood curative

value of liver-rich source of Vitamin A

Vitamin A

• Retinoids –– Preformed vitamin A– Fish and organ meats

• Carotenoids– Provitamin A

• Beta-carotene – Precursors to Vitamin A

Vitamin A

• Liver– Clears Vitamin A from chylomicrons– Main storage place– Targets – most cells of body– Retinoid form greatest concentration

Vitamin A

• Deficiency - most common cause of nonaccidental blindness

• Required in eye for:– Transforming light into neural signals needed

for vision– Maintain cellular differentiation for

• Conjunctival membranes• Cornea• Ocular structures

Fig. 16.39

Vitamin A

• Deficiencies– Night blindness

• Inability to adjust to dim light– Xeropthalmia

• Decreased mucus production - dry eyes – Epithelial cells

• Barriers against infections– Growth, development, reproduction

• Prevents fetal malformations• Failure of embryo to develop

Fig. 15.11

Vitamin A

• Cardiovascular disease– Maybe through antioxidant properties

• Carotenoids

• Cancers– Animal studies primarily– Skin, breast, liver, colon, prostate, lung – Prevent or delay

Vitamin A

• Toxicity– Retinoids may expand and destabilize

membranes• Joint and bone pain

– Teratogenic effects• Spontaneous abortions• Birth defects (1st trimester)

Vitamin A

• Sources– Dark green and yellow-orange vegetables

• Spinach, broccoli, carrots, sweet potatoes

Food Sources of Vitamin A

Recommended Amounts for Vitamin A

• 900 ug RAE (retinol activity equivalents) for men

• 700 ug RAE for women• Daily Value is 1000 ug (RAE)• Upper Level is 3000 ug or 10,000 IU

(RAE of preformed)• Much stored in the liver• No separate RDA for carotenoids

Vitamin D

• Prohormone• Cholesterol-like substance converted to

prohormone D• Enzymes in liver and kidneys convert to

active hormone form• Synthesized from sun exposure (90%)

– Sunscreen SPF >8 decreases synthesis 95%– Expose hands, face, arms 2-3 x/week for 5-10

minutes each time (more for darker skin)

Vitamin D

• Insufficient sun exposure makes this a vitamin

• Use stored Vitamin D in winter, need dietary source

• 80% of dietary Vitamin D absorbed

Functions of Vitamin D

• Regulates blood calcium– Along with the parathyroid hormone– Regulates calcium + phosphorus absorption

• From intestine– Reduces kidney excretion of calcium– Regulates calcium deposition in bones

• Influences normal cell development– Linked to reduction of breast, colon, and

prostate cancer

Role in Bone Formation• Vitamin D hormone

– Causes calcium + phosphorus to deposit in the bones– Strengthens bones

• Rickets is the result of low vitamin D – Breastfed infants with little sun exposure– 1650 recognition of disease– 1822, 1889 observations regarding urban vs rural– Cod liver oil – remedy (18th, 19th centuries)– 1930’s addition of provitamin D to milk

• Osteomalacia (soft bones) – Rickets-like disease in adults– Bones lose minerals and become porous

Food Sources of Vitamin D

• Sources– Fatty fish (salmon, herring)– Fortified milk, yogurt– Some fortified cereal

• Food not a significant source of Vitamin D• Casual sun exposure usually sufficient

Adequate Intake (AI) for Vitamin D

• 5 ug/d (200 IU/day) for adults under age 51

• 10-15 ug/day (400 - 600 IU/day) for older adults– May need combination of fortified foods

and supplements

Toxicity Warning

• Vitamin D can be very toxic, especially in infancy and childhood

• Upper Level is 50 ug/day• Results in

– Over-absorption of calcium (hypercalcemia), – Calcium deposits in organs and blood

vessels– Growth retardation– Cell death

• Tanning does not result in toxic levels

Fig. 05.16a

Fig. 07.20

Vitamin E

• Vitamin looking for a disease• Role in some metabolic function? • Vitamin E activity depends on “antioxidant

network”– Antioxidants and antioxidant enzymes

maintain E in unoxidized state– E ready to intercept and scavenge radicals

• Prevents spread of free radical damage in cell membranes, DNA, cell components

Vitamin E

• Fat-soluble antioxidant

• Resides mostly on cell membranes

Food Sources of Vitamin E

Vitamin E

• Benefits– May help prevent cardiovascular disease– Cancer – Improves vitamin A absorption– Helps metabolize iron in cells– Maintains nervous system, immune function

Vitamin E

• Upper Level is 1,000 mg/day (supplementary alpha-tocopherol)– Most active form

• Upper Level is 1500 IU (natural sources) or 1100 IU (synthetic forms)– Research ongoing regarding excess intake

Vitamin E

• Toxic effects– Inhibit vitamin K metabolism and

anticoagulants • Reduced clotting

– Possible hemorrhage– Muscle weakness, headaches, nausea

Vitamin K (“Koagulation”)

• Synthesized by bacteria in the colon and absorbed– 10% of that needed– Balance comes from diet

• Role in coagulation process– Activates blood-clotting factors

• Role in calcium-binding potential– Activates proteins that help Ca binding in

bone, muscle, kidneys

Vitamin K

Food Sources of Vitamin K

• Liver• Green leafy vegetables• Broccoli• Peas• Green beans• Resistant to cooking losses• Limited vitamin K stored in the body

Adequate Intake for Vitamin K

• 90 ug/day for women• 120 ug/day for men• Excess vitamins A and E

– Interferes with vitamin K– May cause hemorrhage and fractures

• Newborns – Routinely injected with vitamin K– Breast milk is a poor source

• Toxicity unlikely; readily excreted

Fig. 18.16