Dying from too much water

Gina Kolata writes in the NY Times:

Dr. Lewis G. Maharam, the medical director for the New York City Marathon and marathons in San Diego, Phoenix, Nashville and Virginia Beach, said he was taking every opportunity this year to educate runners about the biggest threat to their lives on race day - drinking too much water.

... in their zeal to avoid becoming dehydrated, runners may end up drinking so much that they dilute their blood. Water rushes into cells, including cells of the brain. The swollen brain cells press against the skull, and the result can be fatal. The resulting condition is known as hyponatremia - too much water.

"There are no reported cases of dehydration causing death in the history of world running," Maharam said. "But there are plenty of cases of people dying of hyponatremia."

The article doesn't say, but hyponatremia is really too little salt (sodium) in the blood. So health experts have been giving us two pieces of bad advice: that increased water intake is always good, and that decreasing salt intake is always good. Table salt has no known adverse health effects in people with normal blood pressure.