Water: Can it Be Too Much of a Good Thing?

THURSDAY, Nov. 3, 2016 (HealthDay News)

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Dehydration is a familiar foe for endurance athletes, and one that will be on the minds of every participant in Sunday's New York City Marathon.

But did you know that drinking too much water can be potentially fatal, particularly if not treated properly?

And you don't have to be an elite athlete like a marathoner to fall victim to what doctors call water intoxication.

Water intoxication occurs when a person has consumed so much water that the salt levels in the blood become diluted, said Dr. Aaron Baggish, co-medical director of the Boston Marathon.

"When sodium [salt] concentrations are low in the blood, it actually allows water to leak out of the blood into the other tissues," a condition known as hyponatremia, added Baggish, who's also associate director of the Cardiovascular Performance Program at the Massachusetts General Hospital Heart Center.

The brain appears to be the organ most affected by hyponatremia, and begins to swell as water leaks out of blood and into brain cells, he said.

Usually, the symptoms are mild, such as confusion, headache and nausea. But if left untreated, people might wind up suffering seizures, Baggish said.

In the worst cases, the brain continues to swell uncontrollably, resulting in a potentially fatal condition called brain stem herniation, he said.

"The brain is soft tissue that's contained in a fixed skull. When the brain swells, there's only one real way it can go as an exit path, and that's down to the bottom of the skull where there's a hole that connects the brain to the spinal cord," Baggish said.

Death from water intoxication is very rare among athletes like marathon runners, said Dr. William Roberts, a former president of the American College of Sports Medicine.

"We've noted maybe a half dozen deaths out of probably 3 or 4 million finishers, so it's not a very common cause of fatality," said Roberts, who's also a professor with the University of Minnesota's Department of Family Medicine and Community Health. Marathon runners are more likely to die from a heart attack or heat stroke, he said.