The Down Side of Hydrating

Drinking too much water during athletics can be dangerous.

By Stephen Hanks

May 2006

When it comes to deciphering nutritional advice, there are contradictions at every turn. One day eating carbs will make you fat and the next it’s the greatest thing since sliced bread. Or one minute drug X will reduce your cholesterol count and the next it might make your kidneys malfunction. But there used to be a health truism you could trust—you can never drink too much water, especially when you exercise or are dehydrated. Now experts say even that health rule of thumb is a fallacy.

Meet hyponatremia, a condition caused by drinking too much water during prolonged exercise sessions. What are the symptoms? Nausea, headaches, muscle cramps and even seizures. It’s hard to believe that any athlete could suffer from what is also called “water intoxication,” but according to the MayoClinic.com, overdrinking can dilute the sodium in the bloodstream (especially in older adults, among whom low blood sodium is more common). This can cause the brain to swell and push against the skull, which could lead to coma and death.

Sweating It Out

Basically, here’s how hyponatremia happens: We need sodium to draw water through permeable membranes (such as those that surround cells) and to distribute fluid throughout the body. When we sweat, we lose water and salt, which is made up of sodium and chloride. So lots of sweating depletes the body of sodium. If sodium levels in the bloodstream fall too much, water cannot move across the membranes properly and we become dehydrated. When that happens we could drink a river of water and we wouldn’t have enough sodium to move it from the gastrointestinal tract to the blood.

In 1998, an athlete named Bob Irving competed in a Half Ironman competition and drank so much water during the race he made himself sick; he cramped up and had to walk most of the 13.1-mile run. And last year, officials at the Houston Marathon cut in half the number of water stops because in previous years so many runners were showing up at the medical tent suffering from hyponatremia. So while this condition may not be widespread, it is serious enough to make one cautious. That’s especially true of women, who are smaller and therefore more susceptible to fluid overload.

Water Wise

What constitutes drinking too much? If you’re a serious runner, the International Marathon Medical Directors Association recommends that, during extended exercise, athletes drink no more than 31 ounces of water per hour.

There are other things you can do to prevent hyponatremia besides not overdrinking. During a long competition, try to eat salty snacks such as pretzels, especially if you’re a person who sweats profusely (salty sweaters usually have a white residue on skin and clothes). Sports drinks filled with electrolytes can be more beneficial than water during competition, but don’t overdrink those, either. Most importantly, if you experience any of the warning signs, stop your activity, get medical help and, of course, stop drinking.

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