For Marathoners, Carbohydrate Loading Is Not Enough

From the WebMD Archives

May 5, 2000 -- Seven marathoners were admitted recently to an ER with nausea, vomiting, mental confusion and pink, frothy fluid in their lungs. All of them had the potentially fatal condition pulmonary edema, in which fluid accumulates in the lungs. All but one of the patients were tested and treated for excess fluid in the brain. The seventh patient was not tested for edema and died from the fluid in the lungs and brain.

Doctors who studied these cases found that the main culprit was sodium loss during intense exercise, causing the excess fluid to build up in the brain and lungs.

"Heat stroke isn't the only reason that runners collapse after marathons," study author J. Carlos Ayus, MD, tells WebMD. "And if left untreated, sodium loss can be fatal."

Ayus, a kidney specialist and professor at Baylor College of Medicine in Houston, and his colleagues published their findings in the May issue of Annals of Internal Medicine. They report that diagnostic tests showed sodium losses of up to 13%. The patients were placed on ventilators and treated with intravenous salt solution. Over 12 hours, lung fluid and brain swelling decreased as sodium levels increased.

The authors believe low sodium first causes brain swelling, which then causes a build up of fluid

in the lungs. "Doctors need to be aware of the association between these two conditions," says Ayus, "because successful therapy depends on it."

During exercise, blood is directed from the stomach to the muscles, causing ingested fluid to remain in the gut. After exercise, blood returns to the stomach, allowing ingested fluid to be quickly absorbed by the bloodstream. But because marathoners have sweated for hours, this high volume of fluid is often low in sodium.

To prevent sodium loss, sports medicine experts advise sodium loading. "Marathoners should use table salt before races, drink sports beverages during races, and eat salted pretzels in the last half," says Lewis Maharam, MD. Maharam, the medical director of two marathons and a board member of the International Medical Marathon Directors Association, commented on the study for WebMD.


All the marathoners in the study had taken drugs such as aspirin, ibuprofen and naproxen sodium.

"Research has shown that ibuprofen (Advil and Motrin), ketoprofen (Orudis), and naproxen sodium (Aleve) affect kidney function. So only acetaminophen (Tylenol) should be used after midnight on race days," says Maharam. "But all of them are good for muscle pain afterward, once nausea has resolved and urine is clear yellow."

Maharam cautions that women are at special risk of depleting their sodium levels. "Women appear to have a higher risk for sodium depletion than men, but not because of physiology," he says. "Most first-time marathoners are women and they're still learning. Fortunately, most women don't develop any symptoms."

But for those who do, medical personnel use a standard protocol for exercise-related collapse. "We use a series of simple techniques to stimulate blood flow to vital organs," says Maharam. "But if racers don't feel better after 30 minutes, we transport them to a local hospital."

Before local marathons, emergency physicians are briefed on patient care.

"We treated and released four women with sodium loss during a recent marathon," Sterling Huff, DO, tells WebMD. The medical director of emergency services at Houston's St. Joseph's Hospital adds, "But we were coached to check sodium immediately, and it made a big difference in patient outcomes."

Vital Information:

  • Sodium loss from intense exercise can cause excess fluid in the brain and lungs. Symptoms include nausea, vomiting, headache, seizures, and large amounts of pink saliva.
  • Emergency treatment includes intravenous therapy with salt solution.
  • To prevent sodium loss, marathoners should use table salt before races, consume sports drinks during races, and eat salted pretzels in the second half.
  • Some over-the-counter pain medications such as ibuprofen, ketoprofen, and naproxen sodium affect kidney function; only acetaminophen should be used after midnight on race days.

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