Drinking too much water while running a marathon can kill you. That may sound like a rumor passed around on the Internet, but it does happen in some cases. Now researchers at the University of California, San Francisco think they know why. The excess water can help to cause the brain to swell, and fluid to leak into the lungs, either of which can be fatal. They confirm that the cure is a simple intravenous dose of salt water. The findings are published in the May 2 issue of the Archives of Internal Medicine.
Although marathon runners need to keep hydrated, in the last decade physicians have come to realize that a few hours of sweating away water and salt, but drinking only water, could put some runners into a danger zone known as hyponatremia. It was found that some runners who collapsed and died during a marathon had lost the normally well-balanced ratios of salt and water -- they had plenty of water, but far too little salt.
To understand how this might kill some runners, Allen Arieff, MD, a UCSF professor of medicine at the Veterans Affairs Medical Center in San Francisco, and two colleagues at Baylor College of Medicine, treated, or consulted on the cases of, seven athletes who suffered hyponatremia while running a marathon. They had all been nauseous, vomiting, or confused at some point during their run. Six of the seven patients survived after intravenous treatment with a high salt solution.
All the patients share several characteristics, which provide clues about the mechanisms of hyponatremia, Arieff said. In addition to having fluid in their lungs -- a hallmark of hyponatremia -- the patients all had low levels of sodium and oxygen in their blood. X-rays of six of the patients showed that they had significant brain swelling.
In the study, Arieff suggests the following mechanism. The body, in an attempt to keep a balance of salt and water levels between the blood and tissues, begins to draw water out of the blood, leading
Contact: Kevin Boyd
University of California - San Francisco