Harvard Men's Health Watch

On call: Hydration for summer exercise

On call

Hydration for summer exercise

Q. I've always been told that it's important to drink plenty of fluids during exercise, and it seems to work for me. But now I've read that too much water can be very dangerous. Which is right?

A. Both are right: good hydration is important, but overhydration can be hazardous, even lethal. Fortunately, common sense and moderation will protect you from both extremes.

Until the late 1970s, most athletes were advised not to drink before or during exercise. The idea was to avoid bloating and to improve performance. Some coaches may have also believed that withholding fluids would "build character." It didn't work. In fact, dehydration increases the risk of muscle cramps, heat exhaustion, and heat stroke during exercise in warm weather. And even in mild weather, dehydration can leave exercisers grumpy or groggy for hours afterward.

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