Key Tips on Hydration (Volume 4)

Hydration status and dehydration

Index

• Measuring hydration status.

• Hydration and chronic diseases.

• Signs and symptoms of dehydration.

 

MEASURING HYDRATION STATUS

KEY TIPSON HYDRATION

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Normal hydration status is the presumed condition of healthy individuals who maintain water balance1. Evaluation of hydration status is not easy, as during daily activities or exercise, fluid compartments are constantly fluctuating and therefore the evaluation of a single body fluid compartment volume is insufficient to provide valid information about total body water (TBW)2.

• Urine indicators: Volume and colour Specific gravity/osmolality

• Thirst• Plasma osmolality

• Plasma sodium concentration• Blood urea nitrogen• Saliva specific gravity• Bioelectrical impedance spectroscopy

• Body weight differences

Body weightx 0.6

70 kgTotal

body water(TBW)42 L

Intracellular fluid (ICF)

28 LInterstitialfluid (ISF)

10.5 LCell membrane

Capillary wallExtracellular fluid (ECF)

14 L

2/3

1/31/4 Plasma - 3.5 L

3/4

There are many hydration assessment techniques. The following are some of the methods used1-3:

BODY WATER COMPARTMENTS*

* Adapted from: Elsevier, Inc. Netterimages.com. http://www.netterimages.com/images/vpv/000/000/021/21248-0550x0475.jpg

An acute change in hydration status over a period of a few hours can be assessed by:

Hydration status can be assessed by:

We will focus on some techniques that are simple, easy to perform, and inexpensive, but also reliable, so that they can be used to evaluate hydration status during daily activities.

KEY TIPS ON HYDRATION

URiNE iNDiCATORSColourUrine colour correlates quite well with hydration status as assessed by plasma osmolality and other markers especially when measured on the first sample of the day, but it can be influenced by dietary factors and medications3. Nevertheless, it provides a useful estimate of hydration state during everyday activities2. The chart to the right shows that darker coloured urine is associated with an increased likelihood of dehydration.

VolumeIn a healthy adult a urine output of 1-2 litres per day may indicate good hydration while outputs of less than about 500 mL per day can indicate deficient hydration status. An output of more than about 300 ml per hour suggests excessive fluid intake1. Frequency of passing urine is a related parameter that might also give a rough guide. Physical activity and heat exposure can reduce urine output because of the loss of water in sweat, while cold stress can increase it2.

Specific gravityNormal (euhydrated) values range from about 1,010 to 1,020 and slightly over after overnight dehydration4. When serious hypohydration exists, urine specific gravity may exceed 1,0305.

Other urine indicators, including urine osmolality may also be used as indicators of hydration status6, but are less easy to measure.

1. EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. Available online: www.efsa.europa.eu/en/efsajournal/pub/1459.htm 2. Kolasa KM, Lackey CJ, Grandjean AC. Hydration and Health promotion. Nutrition Today 2009;44:190-201. 3. Panel on Dietary Reference Intakes for Electrolytes and Water (2005) Dietary reference intakes for water, potassium, sodium, chloride, and sulphate. National Academy Press: Washington DC. 4. Casa DJ, Armstrong LE, Hillman SK, Montain SJ, Reiff RV, Rich BSE, et al. National Athletic Trainers’ Association position statement: fluid replacement for athletes. J. Athletic Training 2000;35(2):212-224. 5. Armstrong LE. Assessing hydration status: the elusive gold standard. J Am Coll Nutr. 2007;26(5S):575SY584S. 6. Shirreffs SM, RJ Maughan. Urine osmolality and conductivity as markers of hydration status. Med Sci Sports Ex (1998) 30: 1598-1602. 7. Farrell MJ, Egan GF, Zamarripa F, Shade R, Blair-West J, Fox P, et al. Unique, common, and interacting cortical correlates of thirst and pain. Proc Natl Acad Sci U S A. 2006;103(7):2416–21.

the following information relates to healthy young and adult people. For healthy children and healthy elderly people, or those with pathological conditions, the responses indicating normal hydration (euhydration) may be different from those indicated below.

examPLe oF How urine coLour migHt vary witH

Hydration status

Pale yellow:Hyperhydration – overhydrated

Pale yellow:Hyperhydration – overhydrated

Amber-orange:Euhydration – optimally hydrated

Rich golden amber:Hypohydration - partially dehydrated.

Mid-brown:Severe dehydration

Mid-brown:Severe dehydration

Amber-orange:Euhydration – optimally hydrated

Rich golden amber:Hypohydration - partially dehydrated.

Probably adequately hydrated

Possibly dehydrated

Probably dehydrated

Possibilmente disidratato

Probabilmente disidratato

Probabilmente idratatoin modo adeguato

Posiblemente deshidratado

Probablemente deshidratado

Probablemente adecuadamentehidratado

ThiRSTThirst is triggered by both perceptual (taste, colour, flavour, temperature of beverages) and physiological mechanisms (increases in plasma (ECF) sodium concentration and osmolarity, reductions in plasma volume) at water deficits which correspond to a body weight loss of about 3% or more1. Several scales have been developed to quantify the feeling of thirst7. Individuals can learn to recognise their own thirst responses to various levels of dehydration.

BODY WEighT DiffERENCE MEASUREMENT is a sensitive, accurate and easily measured indicator of change in hydration status when measured regularly and under standard conditions1. This technique is especially appropriate for measuring dehydration that occurs over a period of 1 to 4 hours. The base is simple: body weight loss is approximately equal to sweat loss (corrected for the weight of fluid and food consumed and urine and faecal losses)2. Other factors influencing body weight should be carefully controlled. For example, carbohydrate loading in athletes will increase body weight by retaining water with glycogen stored in muscle1.

note: colour reproduction may not be accurate, do not use this chart for diagnostic purposes.

HYDRATION AND CHRONIC DISEASES

KEY TIPSON HYDRATION

FOR HEALTHCARE PROFESSIONAL DISTRIBUTION ONLY

Dehydration is the process of losing body water and can eventually lead to hypohydration, the condition of body water deficit, when intake of fluids and water included in food is insufficient to keep the body hydrated1,2. Hypohydration may have an effect on cognitive and physical performance, and also on the health status1-8.

Severe hypohydration (involving a loss of more than 10% of body weight) is a well-known cause of mortality. However, there is increasing evidence that mild hypohydration (involving a loss of 1-2% of body weight)1 may also contribute to different diseases3,8.

Low habitual fluid intake leads to chronic hypohydration, which is likely to be mild. In contrast, symptoms of acute mild hypohydration may be severe4.

CHRONIC MILD DEHYDRATION

Maintenance of good hydration has been shown to reduce the risk for these conditions6.

can be present in many individuals failing to meet daily water requirements, but it has been shown to be a common condition in some population groups, including the elderly and those who participate in physical activity in warm environments5.

Some studies have shown an association, although not necessarily a causal one (see different levels of scientific evidence*), between a low habitual fluid intake and some chronic diseases3,6-8, such as: • urolithiasis and cystic fibrosisIb; • urinary tract infections, exercise asthma, hypertonic dehydration in the infant, and hyperglycaemia in diabetic ketoacidosisIIb; • constipation, hypertension, fatal coronary heart disease, venous thromboembolism, glaucoma, and strokeIII; • dental diseaseIV.

Evidence is also available, but inconsistent for bladder and colon cancer3,6.

*Categories of evidence are as follows: Ib: Evidence from at least one randomised, controlled trial; IIb: Evidence from at least one other type of quasi-experimental study; III: Evidence from descriptive studies, such as comparative studies, correlation studies, and case control studies; IV: Evidence from expert committee reports, opinions or clinical experience of respected authorities, or both.

KEY TIPS ON HYDRATION

**See our educational materials about effects of dehydration, how to measure hydration status and water intake recommendations at: http://www.europeanhydrationinstitute.org/educational_materials.html

1. EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. Available online: www.efsa.europa.eu/en/efsajournal/pub/1459.htm 2. Institute of Medicine: Dietary reference intakes for water, potassium, sodium, chloride, and sulfate. Washington, DC: The National Academies Press, 2005. 3. Manz F. Hydration and disease. J Am Coll Nutr 2007;26(5):535S–541S. 4. Maughan RJ. Hydration, morbidity, and mortality in vulnerable populations. Nutrition Reviews 2012;70(Suppl. 2):S152–S155. 5. Maughan RJ. Impact of mild dehydration on wellness and on exercise performance. Eur J Clin Nutr 2003;57(Suppl):S19–S23. 6. Manz F, Wentz A. The importance of hydration for the prevention of chronic diseases. Nutrition Reviews 2005;63(6):S2-S5. 7. Popkin BM, D’Anci KE, Rosenberg IH. Water, Hydration and Health. Nutr Rev 2010;68(8):439-458. 8. Brocker C, Thompson DC, Vasiliou V. The role of hyperosmotic stress in inflammation and disease. Biomol Concepts 2012;3(4):345-364. 9. Kolasa KM, Lackey CJ, Grandjean AC. Hydration and Health promotion. Nutrition Today 2009;44:190-201. 10. Manz F, Johner SA, Wentz A, Boeing H, Remer T. Water balance throughout the adult lifespan in a German population. Br J Nutr 2012; 107(11):1673-81.

PRACTICAL TIPS TO MAINTAIN A GOOD HYDRATION STATUS• In healthy people, adequate hydration can usually be maintained with normal drinking behaviour

and by responding to thirst2.

• With age, the body loses its ability to have a thirst response to fluid deficit2. Drinking regularly is therefore desirable to maintain good hydration2. Common antihypertensive medications may also affect the thirst mechanism.

• Water replacement can be enhanced by consuming beverages at meals and in other social situations2.

• Monitoring hydration status is recommended. Assessing urine colour provides a useful estimate of the hydration state during everyday activities9**.

GROUPS PARTICULARLY VULNERABLE TO DEHYDRATION:

• The elderly: Dehydration is commonly believed by geriatricians to be an acute precipitating factor for hospital admissions, with added heat stress probably increasing symptoms4.

• Infants and children are more susceptible to dehydration than adults. Special care has to be given during periods of frequent vomiting or diarrhoea.

SOURCES OF WATER IN THE DIET:

• It is calculated that of the total water needed:

The adequate intake of water recommended by EFSA1** varies with age and gender and provides a guideline water intake. However, individual requirements will vary according to factors such as environmental temperature and level of physical activity.

70-80%from beverages (all types, not just plain water)1,10.

20-30%typically comes from food and

However, this may vary greatly depending on the diet that an individual chooses1,10

Recognising signs andsymptoms of miLd dehydRation

KEY TIPSON HYDRATION

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Fluids are continuously lost from the body. Water is lost via respiration and through the skin, renal system, and gastrointestinal tract1 and this water needs to be replaced. The daily water requirement depends on a number of factors including the person’s diet, environment, age and activity level1. For adolescents over 14 years old and adults the European Food Safety Authority (EFSA) has given an adequate water intake of 2 L for females and 2.5 L for males*2.

Dehydration occurs when the body loses more water than it takes in. Mild dehydration (equivalent to a 1-2%2 decrease in body mass) may have an effect on performance and may lead to an increased risk of adverse health outcomes3:

Physical performance: Dehydration can adversely affect exercise performance and it is estimated from research that dehydration equivalent to 2% of body

mass loss is where a negative effect on endurance performance may occur4.

Cognitive performance: Acute dehydration - such as that resulting from 2 hours exercising in the heat- can indeed affect mental performance. However, in situations where less severe dehydration occurs (such as when refraining from drinking for a relatively short period of time) authors have generally failed to find evidence of cognitive impairment5.

Disorders and Disease: There is strong evidence for an association between chronic systematic mild dehydration and urolithiasis, urinary tract infection, hyperglycaemia in diabetic ketoacidosis, and mitral valve prolapse. Association with constipation, hypertension, coronary heart disease, stroke, venous thromboembolism, dental disease, gallstones, and glaucoma is less strong6.

Is your physIcal performancelower than usual?

Do you feel tIreD anD lethargIc?

are you constIpateD?

These mighTbe signs ofmild dehydration

* please consult our educational material section at the address below to check water adequate intakes for other ages and special conditions. www.europeanhydrationinstitute.org/educational_materials.html

KEY TIPS ON HYDRATION

signs and symptoms of dehydRation may incLude:* thirst3

* tiredness3

* palpitations due to an increase in heart rate7

* increased body temperature as a result of decreased blood flow to the skin and sweating compromising thermoregulation7

although these signs and symptoms are neither specific nor sensitive, it is important to consider whether dehydration might be the cause.

70-80%from beverages(all types, not just plain water)2,8

20-30%typically comes from food and about

most people drink in response to thirst, and in many cases this is enough to avoid dehydration. however, it is important to take into account that the regulatory mechanism impairs with age, and it may not always be possible to drink when thirst arises.

under special circumstances, when large amounts of water and electrolytes are lost due to vomiting, diarrhoea, or even sweating (e.g. after intensive sport or during hot weather), oral rehydration salt solutions or electrolyte solutions are needed.

In order to ensure an appropriate amount of water, it is important to take into account that of the total water consumed, about:

However, this may vary greatly depending on the diet that an individual chooses2,8

1. Panel on Dietary Reference Intakes for Electrolytes and Water (2005) Dietary reference intakes for water, potassium, sodium, chloride, and sulphate. National Academy Press: Washington DC. 2. EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. Available online: www.efsa.europa.eu/en/efsajournal/pub/1459.htm 3. Kolasa KM, Lackey CJ, Grandjean AC. Hydration and Health promotion. Nutrition Today 2009;44:190-201. 4. Cheuvront SN, Carter R, Sawka M. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2003;2:202-8. 5. Szinnai G, Schachinger H, Arnaud MJ, Linder L, Keller U. Effect of water deprivation on cognitive-motor performance in healthy men and women. Am J Physiol Regul Integr Comp Physiol 2005;289(1):R275-80. 6. Manz F, Wentz A. The importance of good hydration for the prevention of chronic diseases. Nutr Rev. 2005;63:S2-S5. 7. Kavrouras SA, Anastasiou CA. Water physiology. Nutrition Today 2010;45:S27-S32. 8. Manz F, Johner SA, Wentz A, Boeing H, Remer T. Water balance throughout the adult lifespan in a German population. Br J Nutr 2011;1-9 [Epub ahead of print].

     

 

 

 

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