Health: Too Much H2O

If you constantly swig from a bottle of water during strenuous exercise, you're not alone. Coaches, personal trainers and doctors have long harped on the need to avoid dehydration, which can cause dizziness, fainting and, in extreme cases, brain damage or death.

But when a 28-year-old woman collapsed and died during the Boston Marathon three years ago, it wasn't lack of water that felled her. It was too much water. A study in last week's New England Journal of Medicine found that an alarming number of runners and other athletes are risking a similar fate. The problem is that drinking too...

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