Q. I know that exercise is good for my heart, which is one reason why I took up long-distance running. But I have heard that marathon running damages the heart. Is that true?
A. Your question, variations of which have been batted around for more than a century, doesn’t yet have a simple answer.
Back in 1869, a British doctor wondered if prolonged vigorous exercise, like long-distance rowing or endurance bicycling, could damage the heart. Over the years, overwhelming evidence of the benefits of regular exercise for the heart and virtually every other system in the body pushed that concern to the side. But several small studies have raised the question again.
Blood samples given by runners immediately after marathons show increased levels of proteins that indicate possible damage to heart muscle. Blood tests for these proteins, creatinine kinase-MB and cardiac troponin T, are used in emergency rooms to detect heart attacks. It turns out, though, that skeletal muscle also makes and releases creatinine kinase-MB, so the increase could be from the inevitable wear and tear on muscles during a marathon.
A study presented at the 2006 American Heart Association meeting suggested that marathon runners over age 50 may have more calcium in their hearts’ arteries than non-marathoners. But there is no way to know if other differences besides running account for the extra calcium or, more important, if it translates into heart disease.
Long-term studies of elite athletes indicate that they have above-average life expectancies and low risk for heart disease and diabetes in later years. On the other hand, they tend to develop lower-limb arthritis more than the general population. Granted, elite athletes are a biologically and genetically select group who are not representative of the population at large. Yet their long-term health offers a signal that endurance exercise is generally safe.
One point raised by the studies of marathoners will almost certainly pan out: Runners with the least amount of training invariably showed the most worrisome cardiovascular changes after a marathon.
If long-distance running is what keeps you active, then do it. Just use common sense. There’s probably a cardiovascular difference between training regularly, then running the occasional marathon — and running a marathon a day for 50 consecutive days, like Dean Karnazes, author of Ultramarathon Man: Confessions of an All-Night Runner.
— Thomas Lee, M.D.
Editor in Chief, Harvard Heart Letter
