Too Much H20

By MICHAEL D. LEMONICK

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 much water dilutes the blood's normal salt content,

producing a condition known as hyponatremia. The result: excess fluid is sucked from the bloodstream into cells--including brain cells--making them swell. Pressure grows inside the skull, and that can lead to permanent damage, even death.

The study looked at the blood of 488 runners in the 2002 Boston Marathon. An astonishing 13% of them showed clear signs of hyponatremia, and three were at the danger level. The condition is most likely to strike novice runners, as elite athletes don't want to lose seconds by slowing down at the water stations that line race routes--and they know from experience that they don't have to.

Unfortunately, as extreme sports like marathons, long-distance bike rides and triathlons grow in popularity, the number of inexperienced athletes also keeps growing. And unless there is awareness of how dangerous excessive drinking of water can be, some endurance athletes may be at risk. o