A very sad story: a 28-year-old woman participating in a radio station contest died of apparent water intoxication. Basically, she consumed so much water so quickly that her body fluids were diluted, and her electrolytes (most importantly, sodium) fell below a critical threshold.
Many illnesses cause dysregulation of electrolyte concentrations; something as simple as diarrhea can put an individual, especially a child, at risk. Water intoxication in healthy individuals is much less common, but it’s not unheard of: it made news in 2005, in a fatal California fraternity hazing incident, and again last year when anti-hazing legislation inspired by the incident passed. It can also strike marathon runners, who may consume large quantities of water after sweating profusely enough to lose significant amounts of electrolytes. A 2005 New England Journal of Medicine study found that 13% of Boston Marathon runners had measurable post-race hyponatremia (low serum sodium levels); other studies obtained similar results. In 2002, a Boston marathoner died of hyponatremia.
Everyone who watches television commercials knows that you’re supposed to drink an isotonic electrolyte solution (eg., Gatorade), rather than water, to rehydrate during and after exercise. The multi-million dollar sports drink industry was founded on this idea, and it’s true – although the majority of people probably don’t work out hard enough to lose a significant proportion of electrolytes, and I’ve always found the taste of Gatorade more nauseating than dehydration. Yet few people seem to realize that pure water is not only inadequate for replacing lost electrolytes, it can be dangerous. After all, it’s just water, and aren’t we always being told to drink more of it? The answer is yes, within reason: you should drink at least a liter of water each day, more if you’re thirsty. As long as you don’t drink too quickly, have healthy kidneys, and urinate as needed, your body will flush the excess; dehydration is much more common than water intoxication! But beware of fad diets, or any other situation where you’re asked to drink huge volumes of water – especially if you’re low on electrolytes for any reason. Water intoxication is a perfect example of how too much of anything, no matter how innocuous, is bad for you.
More information: the Mayo Clinic on recommended daily water intake