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Eight Glasses of Water Myth
For some people, drinking plenty of water is a very good idea. As we age, for example, many of us grow less sensitive to losses of body water and don't drink when we should. Developing a water habit is a good precaution against dehydration. In addition, researchers have good evidence that people who develop kidney stones can lower their risk of further problems by drinking more fluids. "Those are the only patients we would tell to drink more water," says Alpern.
But there are also people for whom guzzling water is dangerous. According to Dr. Gary Robertson, who studies water metabolism at Northwestern University Medical School in Chicago, these are patients whose bodies have trouble eliminating fluids--for example, those with diabetes who are taking anti-diuretic hormone, or ADH, which prevents the body from losing water. "The excess water cannot be excreted," he says, "and the result is water intoxication, which produces symptoms ranging from mild headache to confusion, coma, seizures and occasionally even death."
Increasingly, says Robertson, doctors are prescribing ADH for conditions such as nocturia, a persistent need to urinate at night, which ruins sleep in many elderly people; and bed-wetting, in both older adults and children. He's aware of one case already in which a diabetic woman taking ADH died of water intoxication after following the advice of an article discussing the health benefits of water.
Of course, if you're healthy, and you're laboring over the stair machine, playing basketball, or even gardening in a hot, dry climate, you're going to need a lot more than a liter to keep you hydrated. But you hardly need a nutritionist or a doctor to tell you that.
"You're dying of thirst," says Alpern. "The thirst mechanism is one of the most powerful and sensitive of all the body's regulatory processes."
Thirst Is Your Best Indicator
Robertson says that this mechanism almost always kicks in when we've lost between 1% and 2% of body water. "There's no evidence that this 1 to 2% decrease is harmful in any way," he says. "Thus, there is really no need to 'prevent' this slight decrease in body water by drinking a specified amount in the absence of thirst."
What if you're sweating and for some reason don't or can't drink? That's when the body will begin to squeeze water from its own tissues, including the brain and the skin. And that's why you may get a headache when dehydrated, and why your skin can look ragged and dry. A tall, cool glass of water or soda or iced tea will soothe your head and revive your skin, in most cases, doctors say--but only if you're dehydrated to start with.
"If you're a normally hydrated person, like you or me," says Dr. David Rish, a dermatologist in Beverly Hills, "then drinking extra water is not going to do anything for your skin. If your skin is dry, and you're hydrated, the best thing to do is apply lotion."
Using Water as a Diet Aid
Perhaps most cruelly of all, there's no good evidence that drinking water significantly curbs appetite. "I think that's mostly an invention of the diet industry," says Carolyn Katzin, a nutritionist in Brentwood who runs the American Cancer Society's nutrition program in California. "A better way to get water is in fruits and vegetables."
A couple of liters of drinking water certainly fill the stomach, researchers say. But you're just as hungry shortly thereafter; and once all that water flows under the bridge, you tend to eat as many calories as you would have without guzzling.
Barbara Rolls, the Pennsylvania State researcher, says water can help you eat fewer calories--as long as it's cooked into food. In a 1999 study, Rolls tallied how many calories 24 healthy adult women ate when served a lunch of chicken and rice. When the chicken and rice were prepared as a casserole and served with a glass of water, the women consumed an average of 392 calories each. When the rice, chicken and water were cooked together into a soup, the women ate an average of only 289 calories each. "And they did not make up for those calories by eating more at dinner," says Rolls.
"This is really the way the body is engineered to get water--in food, in soup, in fruits and vegetables, which are almost all water," says UCLA psychologist William McCarthy, who's also director of science at the Pritikin Longevity Center in Santa Monica. "When we get water in this food matrix, it stays with us for a while. Whereas when we drink liquid water, it goes right through the body. I see all these people carrying around their water bottles like talismans to protect them from disease and weight gain. Well, lots of that water is going into the stomach--and right out."
Not that it's doing any mischief in healthy adults along the way. "You know, I get patients in my office all the time, saying, 'I've been real good, doc, I'm drinking seven glasses of water a day,' " says Alpern. "And I leave them alone. It's certainly not doing them any harm, and it's a lot better than other habits they could have."
So relax, doctors say. Forget the diet books. And listen to your own body. Says Ann Grandjean: "Look, if you're running to the bathroom so much it seems like you can't get any work done, you're drinking too much. And if you're going less than four times a day, you're probably drinking too little."
By Benedict Carey, LA Times
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