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Overhydration: How much water is too much?

Updated on April 27, 2007

Calculate your water needs:

To calculate your hourly water needs, weigh yourself before a one-hour practice run and keep track of how much water you drink during your run. Weigh yourself when you finish and find the difference in pounds from your starting weight (e.g., 0.5 pound). Then multiply that by 15.3 and add that number to the ounces you actually gulped while running. That's how much water you should drink each hour. If you weigh more after a training run, you are drinking too much water and should cut back.


Drink more water, drink more water! The chant can be heard by track couches, marathon volunteers, and runners around the world. And one may think that dehydration would be a runner's worst fear, and although it should be, there is something else that can have just as bad, if not worse effects on the body. Overhydration.

It has been found that some recreational long-distance runners have miscalculate their water needs and drank too much. Overconsumption of water can lead to hyponatremia, a condition that develops when you take in so much water that you disrupt your blood's critical sodium balance. Symptoms include lethargy and disorientation, as well as life-threatening seizures and respiratory distress. The early symptoms of hyponatremia - confusion, lethargy, nausea, vomiting and muscle cramps can mimic dehydration, and an athlete may think the solution is to drink more when he or she actually should drink less. The results can be fatal: As hyponatremia worsens, it results in seizure, coma and death.

Researchers at the Harvard School of Public Health found that 13 percent of Boston Marathon finishers in 2002 were hyponatremic. The most likely sufferers? Slow runners, who stop at every water station, and women, since they usually have less body mass to absorb water than men. "To become hyponatremic, you need to drink a lot of water over a long time," says Benjamin D. Levine, M.D., director of the Institute for Exercise and Environmental Medicine at Presbyterian Hospital of Dallas and a professor of cardiology at the University of Texas Southwestern in Dallas.

A study by Dr. Christopher Almond

A study by Dr. Cristopher Almond ound that thirteen percent of Boston Marathon finishers who participated in the study suffered from hyponatremia (abnormally low blood sodium), mostly caused by overhydrating. Three participants had dangerously low levels of blood sodium.

In a New York Times article about the authors' findings, Dr. Arthur Siegel, a race physician, described the death of a participant in the 2002 Boston Marathon due to hyponatremia. She was five hours into the event at mile 20, stopped and drank 16 ounces, thinking she was dehydrated. She collapsed within minutes and was found to have a blood sodium level of 113 mmoles./liter, normal being between 135 an 145 mmoles/liter. She was later declared brain dead. What went wrong is that the body tries to correct hyponatremia from overhydrating during exercise by transporting excess water into the cells, including brain cells, causing brain swelling.

The study also found a strong correlation between weight gain during the event and hyponatremia. And suggested using spot weight checks before and after a long training session or race as a simple screening tool. If you have gained weight you may have ingested so much liquid that you have given yourself hyponatremia. If you have lost a couple of pounds you may be dehydrated. He added that 87 percent of study participants weren't hyponatremic, so most athletes hydrate correctly. Elite athletes are at much less risk of hyponatremia because they don't stop and drink; if anything, they tend to become dehydrated.


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