Drink as much as you can to avoid dehydration” has become a mantra. But some sports-medicine experts now believe that drinking too much water when exercising poses a far greater risk to health.
Overdosing on water causes changes in blood dilution that trigger the potentially fatal condition hyponatremia. A recent study in The New England Journal of Medicine confirms the problem is on the rise. Researchers claim that, during the 2002 Boston marathon, 13% of the runners drank enough to send their blood-salt levels plummeting to an abnormal low.
How does the danger arise? During intense exercise, the kidneys can’t excrete excess fluid, so if someone keeps drinking, the water is leeched into the body’s cells. The more they drink, the more is retained, especially in the highly water-absorbant brain cells. With no room to expand, the brain pushes against the skull, compressing the brain stem. Eventually, primary functions such as breathing and heartbeat are shut down. ‘Water intoxication can result in dizziness, respiratory problems or worse. Some people collapse into a coma. In the worst cases, it can kill,†says Dr Dan Tunstall-Pedoe of St Bartholemew’s hospital, London, and medical director of the London marathon.
Louise Sutton, head of health and exercise science at Leeds Metropolitan University says: ‘Take care not to over-drink after you finish a workout. Wait until you start urinating for a sign that your body is no longer retaining water.†Dr Tim Noakes, who has conducted research into water intoxication at the University of Cape Town, agrees, saying that bottled-water manufacturers have ‘made dehydration a medical illness to be fearedâ€.
So what if you do become parched at the gym? Surely water is the best way to top up your fluids? Apparently not. In studies on endurance athletes and chronically dehydrated patients in hospitals, drinks containing small amounts of body salts and carbohydrate were more effectively absorbed from the gut than plain water. Sutton says a sports drink, or even orange squash with a pinch of table salt, will get you back into positive fluid balance far more quickly. —