(Agencies)
Updated: 2008-04-03 20:39

NEW YORK - There is no clearcut scientific rationale for the average healthy individual to drink a lot of water -- and it may be downright harmful -- according to two kidney experts.

A volunteer gives out bottles of drinking water after flooding in Tewkesbury, central England, July 24, 2007. [Agencies]

Drinking a lot of water is claimed to be helpful for everything from clearing toxins and keeping organs in tip-top shape to keeping weight off and improving skin tone. At best, however, the evidence to back up these claims is weak, according to a new scientific review published in the Journal of the American Society of Nephrology.

"There is what I call an urban myth that drinking a lot of water is a healthy thing to do and it leads to people toting around plastic water bottles all day drinking water," Dr. Stanley Goldfarb, of the University of Pennsylvania, Philadelphia, told Reuters Health.

"The source of this is the complementary and alternative medicine worlds. If you go on the internet and look up water-drinking and its health implications, that's what you encounter," Goldfarb said.

As a kidney specialist, Goldfarb is interested in how the kidney handles fluids, which prompted him and colleague Dr. Dan Negoianu to review the scientific literature on the benefits of drinking water. In doing so, the researchers debunked four myths.

One is that drinking a lot of water suppresses appetite. "Many people drink water before and during the meal to try to suppress their appetite," Goldfarb explained, yet there is "no consistent evidence" that water suppresses appetite. "Because you absorb water so quickly and it moves through the GI tract so quickly, it probably doesn't fill you up the way people have proposed, nor does it lead to the release of hormones which suppress appetite as far as we know," the researcher said.

The second myth is that filling up on water flushes toxins from the body. "In fact, that is not how the kidney works," Goldfarb said. "When you drink a lot of water you end up having a larger volume of urine but don't necessarily increase the excretion of various constituents of the urine."

The third myth is that it reduces headaches. It does not, according to the evidence. The fourth myth is that water drinking improves your skin. "There are no data to suggest that it actually improves the water content of the skin," Goldfarb said.

Goldfarb and Negoianu did find solid evidence that people living in hot, dry climates, as well as some athletes, have an increased need for water, and people with certain diseases like kidney stones may benefit from increased water intake -- but no such data exist for average, healthy individuals.

Furthermore, there are a couple of circumstances where drinking a lot of water may be actually unhealthy. "In long-distance runners, for example, more harm is done by long distance runners over-drinking during races than by long distance runners who under-drink," Goldfarb explained.

He also cited the case of a woman who developed swelling of the brain and died when she drank water continuously and very rapidly for several minutes as part of a contest.

Goldfarb also said there is no rational basis for the widespread belief that people need to drink eight glasses of water a day, and it is unclear where this recommendation came from.

SOURCE: Journal of the American Society of Nephrology, online April 2, 2008.