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When water is bad for you

A study has found that people who engage in endurance exercise are at risk of getting addicted to water, which can be fatal.

health and fitness Updated: Jun 18, 2007 18:09 IST

A new study has found that people who drink excess water while engaging in prolonged types of endurance exercise are at risk of developing potentially fatal water intoxication.

International experts studied disorders of water metabolism and identified endurance exercise as marathons, triathlons, and long distance cycling.

This serious condition, known as exercise-induced hyponatremia (EAH), could be prevented if only people would respect their personal thirst “metre,” or would assume a “sweat test” to find out how much water they essentially need to drink in order to restore just the body fluids lost during exercising, the researchers say.

Joseph Verbalis, MD, a member of a group of experts working on this condition, recently updated the scientific community on the causes of this disorder in the May issue of Sports Medicine.

“The tragic aspect of the deaths that have occurred from EAH is that these are healthy young people who otherwise would have lived normal, long lives,” said Verbalis.

“The data clearly indicate that EAH is caused by excess drinking during endurance exercise activities, and that it can be prevented by limiting fluid intake while exercising, he says. But despite this knowledge, Verbalis points out that “unfortunately, we are not seeing this condition go away. The public’s impression of the amount of water that is necessary to drink for good health is not based on real factual data,” he adds.

Verbalis points out that EAH principally bothers exercisers engaging in endurance activities of 4 hours in duration or longer. But “the average person who goes out for an hour or two of strenuous exercise is not going to be at risk for this,” he adds.

Verbalis also says that sports drinks, which contain some sodium and potassium and carbohydrates, are essentially water with a few additives.

“There’s a misconception among the sports community that consuming sports drinks rather than water will protect you from becoming hyponatremic. That’s simply not true,” he says. “Drinking too much of anything puts some people at risk for potentially dangerous levels of hyponatremia.”

The disorder occurs when endurance exercisers drink more fluid than their kidneys can excrete. The hormone that determines how much fluid a kidney can excrete is arginine vasopressin (AVP), which is released from the pituitary gland when a person is becoming dehydrated in order to force the kidneys to preserve water. At rest, a person’s AVP level is low and can be suppressed to zero when sufficient fluids are ingested so that the kidney can excrete, rather than retain, excess water. But AVP levels can rise in people who exercise strenuously over a number of hours, even if they are not dehydrated.

Too much water intake in an endurance exerciser whose AVP levels are on the rise means that some of the ingested water will be reserved, and that surplus water can hazardously dilute the level of sodium in the blood that is needed for organs to function, he adds.

The hyponatremia consensus panel has recommended that everyone, including endurance exercisers, should “drink to thirst”, that is, drink only when you feel you need to.

But he adds that endurance exercisers who don’t want to rely on their body’s thirst-meter have another excellent option, and that is undertaking a sweat test. This involves recording a person’s weight digitally, then running on a treadmill for an hour and recording their ending weight after toweling off the body sweat.

“Most people don’t know how much they really sweat while exercising, but this simple test can tell you approximately how much fluid losses you are generating from sweat,” he says. “There is no need to drink significantly more than that, because sweat represents the major source of fluid loss during exercise.”

“So, really, if people just do things in moderation, especially including re-hydrating by drinking, they’re not going to be at risk of either dehydration from excessive sweat losses or EAH from excessive fluid ingestion,” he concludes.

First Published: Jun 18, 2007 17:44 IST