November 2, 1999

When Too Much Water Hurts a Runner


Sports bottles of water have become indispensable accessories in gym bags and symbols of good health. But sports doctors are warning people not to drink too much water during endurance events like the New York City Marathon, which takes place on Sunday.

Steve Berman for The New York Times

Though athletes need to drink regularly during a race to prevent de-hydration, experts say that excess water can lead to hyponatremia, a potentially fatal condition that is rare but increasing among recreational athletes. Hyponatremia is an abnormally low concentration of sodium in the blood. The cause is unknown, but overconsumption of water is thought to increase the risk by diluting blood sodium.

Until recently, hyponatremia was seen almost exclusively in ultramarathons and other extremely high-endurance events, said Dr. Michael Sawka, chief of thermal and mountain medicine at the United States Army Research Institute of Environmental Medicine in Natick, Mass. "Now we're seeing it in marathons, hiking and military occupations," he said.

Symptoms include nausea and vomiting, muscle weakness, headache and disorientation, as well as bloating and puffiness in the face and fingers. In the last year or so, a dozen marathon runners in this country were known or suspected of having hyponatremia, said Dr. William Roberts, a spokesman for the American College of Sports Medicine, the professional organization of sports physicians.

One victim was a 43-year-old woman who died after running the Chicago Marathon last fall.

Doctors are looking for hyponatremia more now than ever before, but they say that increased vigilance does not fully explain the increased diagnoses. Another reason may be that many recreational athletes are drinking too much water. "We've done a good job of educating people on proper rehydration, but some people have taken that to the nth degree, thinking that the more you drink, the better," Dr. Sawka said.

Doctors say that most of the marathon runners with hyponatremia were relatively inexperienced athletes who entered races to raise money for charity. "They're the ones who are in the race for a long time, and there's some speculation that they're drinking too much water during the race," Dr. Roberts said.

The condition seems more common among women than men. Medicine and Science in Sports and Exercise, a journal, recently reported that about half the women studied who finished the New Zealand Ironman triathlon developed hyponatremia, compared with 14 percent of the men.

Doctors are not sure why. It may be that women simply drink more water than men.

The guidelines, set by the sports medicine organization, call for about 17 ounces of fluid two hours before exercise, and then early and at regular intervals to replace all the water lost through perspiration.

Women are especially susceptible to a disorder of recreational athletes.

Dr. Roberts said that people could calculate their "sweat rate" ahead of time by weighing themselves and then exercising for half an hour at the pace and in the conditions anticipated in a coming race. Then they should weigh themselves again to get the number of pounds lost through perspiration.

For every pound lost, they should drink a pint per hour during the race. The guidelines also recommend drinking a sports beverage, like Gatorade, that contains carbohydrates and electrolytes. Sports drinks help prolong an athlete's peak performance and replace sodium lost in perspiration.

Whether sports drinks help prevent hyponatremia is under study, the American College of Sports Medicine says. In any case, doctors say, an effective way for runners to maintain healthy blood sodium concentrations in Sunday's race is to salt their food every day between now and then.