Marathon Runners May Be At Increased Risk For Skin Cancer

Marathon running has become increasingly popular in recent years, according to background information in the article. While regular exercise is associated with improved health, some evidence suggests that endurance exercise--including marathon running--may be linked to skin cancer and other severe illnesses. During training and competition, marathon runners are exposed to high levels of ultraviolet (UV) radiation, the most important environmental risk factor for the skin cancer melanoma. Endurance exercise also may suppress the immune system and increase the risk for malignant melanoma.

Christina M. Ambros-Rudolph, M.D., and colleagues at the Medical University of Graz, Austria, evaluated 210 marathon runners, 166 men and 44 women age 19 to 71 years, for skin cancer risk factors. The runners were recruited at a local marathon and asked questions about their training, including weekly intensity, what type of clothing they typically wore and whether or not they used sunscreen. A group of 210 controls, matched to the runners by age and sex, were recruited at a skin cancer screening campaign. All participants underwent a skin cancer examination and completed a comprehensive questionnaire about personal and family history of skin cancer, changes in skin lesions, sun sensitivity, sunburn frequency and physical characteristics such as skin and eye color.

Controls exhibited higher sun sensitivity than marathon runners, reflected by a larger number of individuals with blue, green or gray eyes and more sensitive skin types. However, the marathon runners had more atypical nevi (moles) and more solar lentigines (small, flat pigmented lesions, sometimes referred to as "liver spots"), higher numbers of which indicate a greater risk for malignant melanoma. These features were more pronounced in those with more intense training regimens. Twenty-four individuals in the marathon running group and 14 in the control group were referred to dermatologists for skin lesions suggestive of non-melanoma skin cancer. Among the marathon group, there was a higher referral rate among those with the highest training intensity.

Seventy-eight (37.1 percent) of the runners ran up to 40 kilometers (about 25 miles) per week, while 101 (48.1 percent) ran 40 to 70 kilometers (25 to 44 miles) per week and 31 (14.8 percent) logged more than 70 kilometers weekly.

Most (203, or 96.7 percent) said they wore shorts and short-sleeved (184, or 87.6 percent) or sleeveless (23, or 11 percent) shirts. These clothing items would not or would only partially cover shoulders, upper arms and legs, body parts that are particularly susceptible to UV radiation exposure. Just more than half--118, or 56.2 percent--of runners regularly used sunscreen while training or competing, while 88 (41.9 percent) used it occasionally and four (1.9 percent) did not use it at all.

These sun-exposure risk factors, in addition to possible weakening of the immune system caused by extreme training, may increase athletes' skin cancer risk. "In short, until further sport-physiologic studies elucidate in detail the potential association between exercise-induced immunosuppression and malignant melanoma, runners should be alerted to the crucial role of UV radiation in the development of malignant melanoma and non-melanoma skin cancer," the authors conclude. "In particular, they should be advised to reduce UV exposure during exercising by choosing training and competition schedules with low sun exposure, wearing adequate clothing and regularly using water-resistant sunscreens."