Are marathons bad for you? Scientists cite heart damage in debate

Research indicates that despite the benefits of exercise, a 26-mile race may be damaging to your heart. Scientists hotly debate the validity of the claim, but few have a concrete answer.
Written by Andrew Nusca, Contributor

Research indicates that despite the benefits of exercise, a 26-mile race may be damaging to your heart.

But how much damage is bad for your health?

In a post on the New York Times Well blog, Tara Parker-Pope writes that scientists are hotly debating the validity of the claim, and rounds up recent research on the subject.

The claim: That the physical exertion of running a marathon is damaging to the heart.

The proof: Last year, the European Heart Journal published a study in which German scientists scanned the hearts of 108 experienced, male distance runners in their 50s, 60s and 70s. More than a third of the men showed evidence of significant calcification or plaque build-up in their heart arteries, and several had scarring of the tissue in their hearts.

The support: Several studies have found elevated levels of cardiac troponin, a substance in the blood that usually suggests cardiac injury, in experienced marathoners.

In a study published in January, Australian doctors found that 32 percent of the runners they tested after the Perth Marathon had elevated levels of troponin -- and the levels did not correspond to how inexperienced or poorly trained they were.

Another study published in July produced similar results among 78 male marathoners. "More than half of the racers wound up with elevated troponin and other cardiac-damage markers," Parker-Pope writes, "There was no correlation between the men’s pace or training and their troponin levels."

Finally, Canadian researchers in January recruited 129 "non-elite" runners in Winnipeg and tested their blood before and after they ran a half or full marathon. Before the race, their blood markers for heart injury were normal. By the end, though, the vast majority showed blood indicators of cardiac damage.

Parker-Pope, again:

“We measure those same blood markers when someone comes in to the emergency room and we suspect a heart attack,” says Davinder S. Jassal, MD, an assistant professor of cardiology, radiology, and physiology at the University of Manitoba medical school in Winnipeg and lead author of the study. Blood profiles like those displayed by the runners, he says, “are similar to those in a very mild heart attack.”

The counter-claim: The markers are false positives and any damage is temporary.

In Winnipeg, a second study of Canadian marathon runners analyzed marathoners' hearts to see if the markers correlated with actual damage, including structural changes or scarring. A week after the race, researchers looked directly into the interior of their hearts and found none of the damage that the markers had suggested would be found.

The catch: It's been suggested that because the original German study used middle-aged runners, smoking in their youth was to blame for the cardiac scarring that was found. Parker-Pope notes that another Canadian study will soon see if scarring can be found in marathoners older than 50 who have no hardening of the arteries.

More research needs to be done, of course, and few debate the value of regular exercise.

But when it comes to extreme activity such as marathons, the question is an interesting one: can you be too fit for your own health?

This post was originally published on Smartplanet.com

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