But it is also important not to get dehydrated. A friend of mine got very sick, and had kidney damage, because he got severely dehydrated.http://www.eurekalert.org/pub_releases/2015-06/luhs-as062915.php
Public Release: 29-Jun-2015
Loyola University Health System
At least 14 deaths of marathon runners, football players and other athletes have been attributed to a condition called exercise-associated hyponatremia, which results from drinking too much water or sports drinks.
But there's an easy way to prevent hyponatremia, according to new guidelines from an international expert panel: Simply put, drink only when you're thirsty.
"Using the innate thirst mechanism to guide fluid consumption is a strategy that should limit drinking in excess and developing hyponatremia while providing sufficient fluid to prevent excessive dehydration," according to the guidelines, published in the Clinical Journal of Sport Medicine.
Exercise-associated hyponatremia (EAH) occurs when drinking too much overwhelms the ability of the kidneys to excrete the excess water load. Sodium in the body becomes diluted. This leads to swelling in cells, which can be life-threatening.
Symptoms of mild EAH include lightheadedness, dizziness, nausea, puffiness and gaining weight during an athletic event. Symptoms of severe EAH include vomiting, headache, altered mental status (confusion, agitation, delirium, etc.), seizure and coma.
[Can also be symptoms of dehydration.]
EAH has occurred during endurance competitions such as marathons, triathlons, canoe races and swimming; military exercises; hiking; football; calisthenics during fraternity hazing; and even yoga and lawn bowling, the guidelines said.
Athletes often are mistakenly advised to "push fluids" or drink more than their thirst dictates by, for example, drinking until their urine is clear or drinking to a prescribed schedule. But excessive fluid intake does not prevent fatigue, muscle cramps or heat stroke.
"Muscle cramps and heatstroke are not related to dehydration," Dr. Winger said. "You get heat stroke because you're producing too much heat."
[From my personal experience, this is misleading. Not drinking enough water can lead to not sweating. Evaporation of sweat cools you off.]
Modest to moderate levels of dehydration are tolerable and pose little risk to otherwise healthy athletes. An athlete can safely lose up to 3 percent of his or her body weight during a competition due to dehydration without loss of performance, Dr. Winger said.
The guidelines say EAH can be treated by administering a concentrated saline solution that is 3 percent sodium - about three times higher than the concentration in normal saline solution.