A new study debunks the usual adage of marathon runners of the "drink-ahead-of-your-thirst" mindset to prevent dehydration. The study emphasizes its point by saying that drinking too much fluids might endanger the lives of runners.
Read the full text of the study here.
Study Cautions Runners to Limit Their Water Intake By Gina Kolata, NYTimes
After years of telling athletes to drink as much liquid as possible to avoid dehydration, some doctors are now saying that drinking too much during intense exercise poses a far greater health risk.
An increasing number of athletes --- marathon runners, triathletes and even hikers in the Grand Canyon --- are severely diluting their blood by drinking too much water or too many sports drinks, with some falling gravely ill and even dying, the doctors say.
New research on runners in the Boston Marathon, published today in The New England Journal of Medicine, confirms the problem and shows how serious it is.
The research involved 488 runners in the 2002 marathon. The runners gave blood samples before and after the race. While most were fine, 13 percent of them --- or 62 --- drank so much that they had hyponatremia, or abnormally low blood sodium levels. Three had levels so low that they were in danger of dying.
The runners who developed the problem tended to be slower, taking more than four hours to finish the course. That gave them plenty of time to drink copious amounts of liquid. And drink they did, an average of three liters, or about 13 cups of water or of a sports drink, so much that they actually gained weight during the race.
The risks to athletes from drinking too much liquid have worried doctors and race directors for several years. As more slow runners entered long races, doctors began seeing athletes stumbling into medical tents, nauseated, groggy, barely coherent and with their blood severely diluted. Some died on the spot.
[NYtimes Health, 14 April 2005]
Putting it simply, the authors of the study say that if you plan to run and drink too much, you are in effect diluting your body's electrolyte supply --- notably sodium --- and exposing yourself to a condition known as hyponatremia or low concentrations of sodium in your blood, which is harmful and can kill you.
How much should you drink then, if you plan to run?
Take this sound advice from expert doctors:
Next time you run, remember that the real danger might not really be dehydration, but drinking too much water. Be careful, okay?
- Dr. Tim Noakes, a hyponatremia expert at the University of Cape Town -
"For their part, runners can estimate how much they should drink by weighing themselves before and after long training runs to see how much they lose - and thus how much water they should replace."
- Dr. Marvin Adner, the medical director of the Boston Marathon -
"Don't start chugging down water. Wait until (you) begin to urinate, (which is) a sign the body is no longer retaining water."
- Dr. Paul D. Thompson, a cardiologist at Hartford Hospital in Connecticut and a marathon runner -
"Drink while you are moving. If you stop and drink a couple of cups, you are overdoing it."