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Drink Wisely During Exercise

Too Much Fluid Can Be As Bad As Too Little

Between the Rock of Fluid Overload and the Hard Place of Dehydration

Fluid overload waters down the blood. It leads to dangerously low salt levels -- a condition known as hyponatremia, in which the blood has too much water and too little sodium. Brain cells absorb too much water and the brain swells. It pushes against the skull, leading to seizures. Finally, a person stops breathing. This is what killed a woman during the 2002 Boston Marathon.

"Humans are actually designed quite well for dehydration," Noakes says. "There is very little evidence it has any effect until one becomes very dehydrated -- by which time your mouth is so dry, and you have such extreme thirst, that this would never happen. You are going to find water or a sports drink. There is no way you will be seriously dehydrated when you start a race."

So How Much Should You Drink?

Not everyone goes quite so far. Other experts who spoke with WebMD agree that it's terribly dangerous to drink too much water or too many sports drinks. But they are uneasy about dehydration.

The USA Track & Field association web site carries advice from Noakes and Douglas J. Casa, PhD. Casa is director of athletic training education at the University of Connecticut.

"I'd bet many more people running Atlanta's Peachtree Road Race were dehydrated than overhydrated," Casa tells WebMD. "I am not downplaying hyponatremia. But the advice of don't drink the water is not good advice for soccer and football players and runners who are out there sweating."

Casa stresses appropriate fluid replacement. So does Leslie Bonci, MPH, RD, director of sports nutrition at the University of Pittsburgh Medical Center. Bonci is the nutritional consultant for the Pittsburgh Steelers and Panthers as well as for the Pittsburgh Ballet Theatre.

"It is not one size fits all," Bonci tells WebMD. "Each and every person doesn't need same amount of fluids. Not everybody has the same sweat rate, the same sodium loss rate."

Safe Use of Water and Sports Drinks

So how do you know how much to drink?

"The solution is not to drown oneself," Bonci says. "Just water alone is not going to be the best recommendation. You also need something with some carbohydrate and some electrolyte in it. So water alone during exercise, no. Drinking until you slosh or drown, no. The guidelines are 20 ounces of fluid before exercise, and over the course of every hour of exercise drink between 28 to 40 ounces of fluid. That is not enormous quantities."

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