Diet, Fitness, and Exercise: Marathoners and Melanoma
Distance runners may be putting themselves at higher risk of skin cancer–and not just because they spend so much time in the sun. Austrian researchers compared 210 marathon runners with 210 nonrunners and found that the marathoners had more of the moles and lesions that are risk factors for melanoma and also were more often referred for follow-up on suspected nonmelanoma skin cancer. Sun exposure, the top risk factor for both melanoma and nonmelanoma skin cancer, is the obvious culprit, says Christina Ambros-Rudolph, a dermatologist at the Medical University of Graz and lead author of the study, which appears in the current Archives of Dermatology. But researchers also suspect that heavy exercise suppresses the immune system and makes the runners more vulnerable to cancer.
No one was actually diagnosed with melanoma, so it's impossible to assign a number to the increase in risk. But previous studies have shown that Ironman triathletes and professional cyclists, who also spend many hours training and competing in the sun, are exposed to high doses of UV radiation, and that sweating heightens the effect by making skin more sensitive to UV rays. While a link to exercise is more speculative, says Ambros-Rudolph, it's thought that tissue damage occurring during intense, long-term exertion may prompt the release of certain proteins that render the immune system less able to fight off skin cancer. (Patients given immunosuppressive drugs after transplants have an increased risk of the disease.) Ambros-Rudolph says her team will look at the link between training intensity and possible immunosuppression.
While the news sounds scary, it shouldn't keep anyone from exercising. First, immunosuppression is suspected only in very intense exercise, not the 30 to 60 minutes daily recommended for good health. Second, the study didn't measure whether the increased risk of skin cancer is offset by the cardiovascular or other health benefits of running. And finally, the study noted that many of the runners simply aren't taking recommended precautions. The bottom line for anyone who exercises outside: Cover up, slather on waterproof sunblock, and avoid working out when the sun is strongest.
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