This article is from the WebMD Feature Archive

Feb. 16, 2001 -- Participants in extreme athletic events, such as marathons and triathlons, are at risk for drinking too much fluid, according to recent research published in the January issue of The Clinical Journal of Sports Medicine.

"Most athletes understand the importance of drinking fluids during these events," Lewis Maharam, MD, tells WebMD. "They don't understand that drinking too much can be just as harmful as drinking too little. Overhydrating can lead to a dangerous condition called hyponatremia, or low blood sodium levels." Maharam, a sports medicine specialist practicing in New York City, is medical director of the New York City Marathon and the Country Music Marathon. He is secretary-treasurer of the International Marathon Medical Directors Association.

Marathoners who stay out on the course for a long time are at risk for hyponatremia, he says, because they lose salt in their sweat. "Those who drink lots of fluids in the days before the race and also stop at every drinking station along the course are also at special risk," he says. "Low blood sodium levels can lead to nausea, fatigue, vomiting, weakness, and sleepiness. In severe cases, it can lead to coma and death."

New Zealand researchers recorded weight changes and fluid intake in 18 participants in the Ironman Triathlon, a competition involving a 2.35-mile swim, 112-mile cycle, and a 26.2-mile marathon run. "The winner usually completes the course in the low eight hours," Allan Goldfarb, PhD, tells WebMD. "The average finisher takes about 12-15 hours." Goldfarb is professor of exercise physiology at the University of North Carolina at Greensboro.

The researchers found that median fluid intake was about one and a half pints per hour, with somewhat higher fluid consumption seen during the cycling section than during other parts of the race. Five participants developed low sodium levels; four of them were women. "[T]he subjects who developed hyponatremia had evidence of fluid overload despite modest fluid intakes, suggesting both a failure of excretion of the fluid and that the fluid needs in some ultradistance athletes may be less than the current recommendations," the authors write.

"There is a new emphasis on prevention in healthcare, and when it comes to exercise, the way to prevent problems is preparation," says Timothy Maggs, DC. "People should train ahead of time in the same conditions they will encounter during the actual race. This is true for all vigorous and unusual exercise, but it is especially important for marathons and triathlons. The only way to determine how we'll respond to certain circumstances is by subjecting ourselves to those circumstances before the actual events." Maggs specializes in sports medicine in Schenectady, N.Y., and is the author of a regular magazine column called "The Running Doctor."

Maharam agrees. He advises participants in long races to take 10 days to two weeks to get used to hot weather, gradually building workout intensity and duration. "Step out of bed every morning and onto the scale," he says. "If you're anywhere from 1% to 3% lighter than yesterday, rehydrate by drinking 8 ounces of fluid for each pound lost before training again."

To avoid hyponatremia, he recommends:

• Check your urine one-half hour before the race. If it is dark and concentrated, drink more fluids.
• During a marathon race, drink 1 cup (8-10 ounces) of fluid every 15-20 minutes along the way.
• Try not to drink more then you sweat.
• Favor a sports drink that has some sodium in it over water, which has none.
• In the days before the race, add salt to your foods (provided that you don't have high blood pressure and your doctor has not restricted your salt intake).
• Eat some salted pretzels during the last half of the race.

Recent research suggests that nonsteroidal anti-inflammatory drugs (NSAIDs) such as Advil, Motrin, and ibuprofen may predispose runners to hyponatremia, Maharam warns. "Acetaminophen (Tylenol) has been shown to be safe," he says. "Therefore, I recommend that you only use acetaminophen, if needed, on marathon day. Do not use NSAIDs until you have finished the marathon, are able to drink without any nausea or vomiting, and have urinated a clear to clear-yellow urine."

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