Its Official, too much water can kill, while dehydration is just bad.
The hyper-linked article cites a Harvard study of runners in the Boston Marathon who drank too much fluid. They say slower runners took more breaks and were more likely to suffer from hyponatremia.
"“Hyponatremia and, particularly, severe hyponatremia may be a greater problem than previously recognized,” said Dr Christopher Almond, the lead author of the study....Dr Marvin Adner, medical director, Boston Marathon, said, “Before this study we suspected there was a problem. But this proves it.” According to hyponatremia expert Dr Tim Noakes, both doctors as well as sports drink manufacturers push dehydration as a ‘medical illness that was to be feared’. “Everyone becomes dehydrated when they race. But I have not found one death in an athlete from dehydration in a competitive race in the whole history of running. Not one. Not even a case of illness,” he said."
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