This archived news story is available only for your personal, non-commercial use. Information in the story may be outdated or superseded by additional information. Reading or replaying the story in its archived form does not constitute a republication of the story.
Dr. Kim Mulvihill reporting It's hard to imagine how drinking too much water can kill you. It's very rare, but it does happen.
Too much water alters the concentration of electrolytes, making it hard for nerves and muscles, like the heart, to function properly.
Water is two-thirds of your body, and three-fourths of your brain. You need two and a half quarts of water a day from what you eat and drink to stay healthy.
But you can get too much of a good thing. In fact, too much water can kill you. It can happen during marathons and triathons, cerain kidney problems or medications or dieretics.
What's common with all of these: too much water and too little salt.
It's called water intoxication or hyponatremia.
Too much water dilutes the sodium in the blood stream, so water is forced into the cells, and tissues swell. Most organs can handle it, but swelling in the brain is a different story, because the brain is trapped by the skull.
Most symptoms are related to cerebral edema, swelling in the brain. Nausea, vomiting, confusion, and weakness. In severe cases, hyponatremia can cause seizures, coma, and death.
But most people don't die. When sodium levels fall slowly over days or weeks, the brain has a chance to compensate, so the symptoms are milder. The real danger is when sodium falls quickly, in just a day or two. Severe swelling occurs, compressing vital midbrain structures, pushing the brainstem out of the skull and into the spinal cord. That leads to respiratory arrest and death.
Once again we want to stress the fact that this is very rare. When it's related to exercise, it's usually more than four hours of strenuous exercise or activity coupled with way too much water.