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How much water am I meant to drink? Is it really eight cups a day?
-- Lily
The notion that we must all drink eight cups of water per day to improve our health is an old one, but it isn't exactly accurate. Although the suggestion dates back to at least the 1940s, the latest to carry the mantel are, unsurprisingly, bottled water companies. Writing in the medical journal BMJ, Glasgow doctor Margaret McCartney pointed out that much of the current recommendations come from events sponsored by Danone, which owns bottled water lines Evian, Volvic and Badoit.
The "8x8 advice" may also endure because, cost aside, it's harmless. And being over-hydrated sure beats dehydration, which can cause headaches, light-headedness, fatigue and other, more serious complaints. Water is essential for proper digestion, kidney function and brain function and is required by every cell of the body. But that doesn't mean we need to sip on it all day.
There may be another reason we've stuck with an inaccurate eight cups -- and that answer isn't nearly so straight forward: the right amount of water to drink is the amount that quenches your thirst.
"When you think about the way that the body handles water, you pee it out. The body regulates water very carefully and doesn't allow it to accumulate. Extra water is immediately excreted," says Dr. Stanley Goldfarb, a professor of medicine at University of Pennsylvania and an expert on fluid management.
What's more, our bodies tell us when we require water -- that's what the thirst mechanism does. Thirst doesn't mean you've reached a dire level of dehydration either. Explains Goldfarb: "When you get thirsty, the deficit of water in your body is trivial -- it's a very sensitive gauge. It might be only a one percent reduction in your overall water. And it just requires drinking some fluid."
Or food: about 20 percent of the fluid we receive each day comes from water-heavy foods like fruits and vegetables.
There is, however, one exception: for those who suffer from kidney stones -- masses of crystals that form in the urine and pass painfully through the urethra -- staying overly hydrated is very beneficial, as it dilutes the concentration of material that forms into the clumps.
The typical U.S. adult downs about four cups a day, which is shy of the Institute of Medicine's recommendation to drink about three liters of fluid for men and 2.2 liters for women. But others disagree with this assessment -- if that's the amount of water a person naturally drinks in response to thirst, that's fine. But there is no benefit to forcing extra water.
Just to reiterate, we're talking exclusively about over-hydration. Beware dehydrating factors like exercise, salty foods and hot weather, and be sure to replace the fluid you've lost. A surefire way to tell if you've replaced your water sufficiently? It's all in your urine. If you're producing pale yellow pee, you've reached a hydrated status. You can keep drinking, but why?
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