How Much Water is Enough? Drowning in Opinions

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It seems like a simple question: How much water should we drink? Whenever the topic comes up, we seem to drown in opinions. Now a Glasgow general practitioner, Margaret McCartney, has stated in the British Medical Journal that the eight glasses per day we’ve all been told to consume is “not only nonsense, but thoroughly debunked nonsense.”

The answer may be in your urine

McCartney takes issue with an initiative called Hydration for Health, which was created and is sponsored by Danone, a large food company that produces bottled waters. Hydration for Health is “recommending 1.5 to 2 litres [50 to 68 ounces] of water daily [as]…the simplest and healthiest hydration advice you can give.”

The initiative’s website states that “many people, including children, are not drinking enough…Children can be at greater risk than adults of feeling the effects of not drinking enough because of their smaller size.” The site also warns that the elderly “often have a decreased sensation of thirst, which can lead to a higher risk of dehydration.”

The general consensus in the medical arena is that the best way to tell if people are getting enough water—from the tap, food, other beverages—is not whether they are thirsty, but by the color of their urine. Light-colored or clear urine means a person is well hydrated, and amber or dark yellow urine usually is a sign of dehydration.

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Signs and symptoms of mild to moderate dehydration include a dry sticky mouth, thirst, dry skin, headache, constipation, dizziness or lightheadedness, sleepiness, reduced urine output, and few or no tears when crying. Severe dehydration, which is a medical emergency, is marked by extreme thirst, very dry mouth, skin, and mucous membranes, lack of sweating, sunken eyes, dark yellow or amber urine, low blood pressure, rapid heartbeat and breathing, and fever.

Dr. McCartney points to research that debunks the eight-glasses-a-day myth, including the work of Professor Heinz Valtin from Dartmouth Medical School. His review in the American Journal of Physiology, entitled “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? stated that “No scientific studies were found in support of 8 x 8,” and that analyses of work in peer-reviewed journals “strongly suggest that such large amounts are not needed.”

The authors of a 2010 report in Clinics in Dermatology on nutrition and water comment on the recommendation to drink six to eight glasses of water daily to keep the skin hydrated and looking healthier. They stated that “we have found no scientific proof for this recommendation,” and that the “only certainty about this issue is that, at the end of the day, we still await scientific evidence to validate what we know instinctively to be true—namely that it is all a myth.”

When dealing with a need as basic as water and hydration, it is helpful to have reliable guidelines from trustworthy authorities. Individuals should discuss the issue with a trusted medical professional if they have questions. But at the end of the day, even though the general recommendation has been to drink eight glasses of water per day, many people do not follow it, myth or no myth.

SOURCES:
McCartney M. British Medical Journal 2011; 343: d4280
Telegraph, July 13, 2011
Valtin H. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 2002 Nov; 283(5): R993-1004
Wolf R et al. Clinics in Dermatology 2010 Jul-Aug; 28(4): 380-83
Picture source: Wikimedia Commons

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