The research is coming in with a resounding yes. "Water
intoxication" is fairly common in long distance events like the marathon
or cycling. According to an article in Annals of Internal Medicine 18%
of marathon runners drink too much water and an article in Medicine and
Science in Sports and Exercise finds that 29% of the finishers in the
Hawaiian Ironman have water intoxication or hyponatremia. The New England
Journal of Medicine states, "We have observed that hyponatremia
occurs in a substantial fraction of marathon runners and can be severe"
and "(It) has emerged as an important cause of race related death and life
threatening illness among marathon runners." Hyponatremia has also become
a common cause of heat illnesses in the Grand Canyon
where people drink too much water and don't eat enough to maintain good levels
of salts and potassium.
What are the symptoms of hyponatremia?
They include apathy, confusion, nausea, and fatigue. If untreated they can
lead to coma or death. Unfortunately, these are the same symptoms of heat
exhaustion or heat stroke and people with these symptoms will often drink even
more water because they think they are dehydrated. A good way for an athlete to
gage how much water she needs is to weigh before and after a race. If weight is
maintained or gained, then she is drinking too much water.
What is happening to the body?
The athlete consumes large amounts of water and blood plasma increases, diluting
salt content. The athlete is also losing salt through perspiration and the
amount of salts available to the body decrease and this interferes with brain,
heart, and muscle function.