Despite
several water intake recommendations,
a better way to monitor hydration levels may be through markers such as urine color (1).
Although
dilution methods to determine total body water via plasma osmolality
measurement are the most accurate, valid, and sensitive ways, they are not
practical for most situations (2,3), but total body mass and urine color when used
in conjunction is a good way to assess hydration status (2,3).
Significant changes in urine color occur within 24 h of modifying
fluid intake volume (16) suggesting that individuals can use urine color
monitoring as a simple way of evaluating the adequacy of their fluid intake (17).
First-morning
urine should look like pale yellow (1), indicating the normal and expected
presence of some waste products from metabolism overnight. This color
corresponds to a state of euhydration (4,5) (it shouldn´t look like water, or
anything dark), 5 clear urinations per day with two after training is a good
rule of thumb.
Thirst
is initially perceived when a body weight deficit of 1–2 % exists (6,7), fluid
consumption should be adequate to avert the perception of thirst. Thirst
signals any imbalances of the osmolality of fluids and tissues (the electrolyte
concentration), and the total amount of water in our body (volume).
Dehydration
Dehydration
is characterized by weight loss, confusion, dry skin that is hot to the touch,
and possibly an elevated core body temperature. In a hot climate, dehydration
can be dangerous and result in thermal injury. Other causes of dehydration can
be excess diarrhea, vomiting due to GI dysfunction, kidney disease, and diuretic
medications.
Thirst
may be a poor measure of hydration because of the lag between the physiological
dehydration and the thirst signal. Special populations require more attention, elderly
are less sensitive to the thirst mechanism due to the deterioration of
osmoreceptor sensitivity (2,8-12); and children are inexperienced in
interpreting the thirst response (13,14).
Older adults are also at higher risk
for reduced kidney filtration function, which results in less efficient water
conservation (when dehydrated), further exacerbating difficulties in recognizing
a dehydrated state (15).
Would you like to know more?
References:
1. Lawrence E. Armstrong (2005).
Hydration assessment techniques. NutrRev 63, S40–S54.
2. Sawka MN, Burke LM, Eichner ER, Maughan RJ,
Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid
replacement. American College of Sports Medicine. Med Sci Sports Exerc.
2007 Feb;39(2):377-90.
3. Sawka M,
Burke LM, Eicher ER, et al. Exercise and fluid replacement. Med Sci Sports
Exerc. 39:377–390.
4. Armstrong
LE, Soto JA, Hacker FT Jr, Casa DJ, Kavouras SA, Maresh CM: Urinary indices
during dehydration, exercise, and rehydration. Int J. Sport Nutr 8:345–355,
1998.
5. Armstrong
LE, Maresh CM, Castellani JW, Bergeron MF, Kenefick RW, LaGasse KE, Riebe D:
Urinary Indices of Hydration Status. Int J Sport Nutr 4:265–279, 1994.
6. Greenleaf
JE, Morimoto T: Mechanisms controlling fluid ingestion: thirst and drinking. In
Buskirk ER, Puhl SM (eds): “Body Fluid Balance: Exercise and Sport.” Boca
Raton, FL: CRC Press,1996.
7. Hubbard RW,
Szlyk PC, Armstrong LE: Influence of thirst and fluid palatability on fluid
ingestion during exercise. In Gisolfi CV, Lamb DR (eds): “Perspectives in
Exercise Sciences and Sports Medicine. Fluid Homeostasis During Exercise.”
Indianapolis: Benchmark Press Inc, 1990.
8. Begum MN
& Johnson CS (2010) A review of the literature on dehydration in
institutionalized elderly. e-Spen Eur e-J Clin Nutr Metab 5, e47–e53.
9. Mentes J
(2006). Oral hydration in older adults: greater awareness is needed in
preventing, recognizing, and treating dehydration. Am J Nurs 106, 40–49.
10. Rolls BJ
& Phillips PA (2009). Aging and disturbances of thirst and fluid balance.
Nutr Rev 48, 137–144.
11. Binkley HM,
Beckett J, Casa DJ, et al. National Athletic Trainers’ Association position
statement: exertional heat illnesses. J Athl Train. 2002;37:329–343.
12. Phillips PA,
Rolls BJ, Ledingham JG, et al. Reduced thirst after water deprivation in
healthy elderly men. N Engl J Med. 1984;311:753–759
13. D’Anci K,
Constant F & Rosenberg I (2006). Hydration and cognitive function in
children. Nutr Rev 64, 457–464.
14. Kenney WL
& Chiu P (2001). Influence of age on thirst and fluid intake. Med Sci
Sports Exerc 33, 1524–1532.
15. Mentes J
(2006). Oral hydration in older adults: greater awareness is needed in
preventing, recognizing, and treating dehydration. Am J Nurs 106, 40–49.
16. Perrier E, Demazieres A,
Girard N, Pross N, Osbild D, Metzger D, Guelinckx I, Klein A. Circadian
variation and responsiveness of hydration biomarkers to changes in daily water
intake. Eur J Appl Physiol. 2013;113:2143–2151. doi: 10.1007/s00421-013-2649-0.
17. Erica T. Perrier Evan C. Johnson, Amy L.
McKenzie, Lindsay A. Ellis, and Lawrence E. Armstrong. Urine colour change as an indicator of
change in daily water intake: a quantitative analysis. Eur J Nutr. 2016;
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