Drink what you need (Image: Donald Miralle/Getty)
Everyone knows the importance of keeping hydrated. Whether it’s a water bottle or a sports drink, athletes and gym bunnies are rarely seen without a source of fluid close at hand. Common advice is to deliberately drink beyond what thirst dictates, or “push fluids”, to combat dehydration and keep performance up to scratch.
Usually that’s a waste of time, and just occasionally it can be fatal. Exercise-associated hyponatraemia (EAH) is a dangerous condition that occurs when people have drunk so much that the concentration of sodium in their blood falls too low. This leads to excess water moving into the tissues of the brain, causing brain swelling. Symptoms include nausea, vomiting and confusion. In rare cases – 12 have been recorded worldwide – the victim has died.
Slower marathon runners, who tend to drink more over the several hours it takes them to complete the course, are one group more likely to develop EAH, and women seem to be more at risk than men. The condition can even be caused by sports drinks claimed to be “isotonic” – meaning that they contain the same concentration of dissolved substances as normal body fluids – as they tend to contain sugar but very little salt.
Cases of EAH rose in the US in the 1990s. Tim Noakes, director of the exercise science and sports medicine unit at the University of Cape Town, South Africa, who was the first to describe the condition, blames the rise on marketing activities by the makers of sports drinks, which he says promote overdrinking (British Journal of Sports Medicine, vol 40, p 567).…
