Researchers have found that marathon runners are at greater risk of developing skin cancer.
They warn that during training marathon runners should use sunscreen or cover up in order to reduce their risk of developing skin cancer.
The researchers at the Medical University of Graz in Austria, found in a study of long-distance runners that athletes training for and taking part in marathons are more likely to develop skin cancer than others; the risk increased along with the level of the intensity of the runner's training schedule.
Dr. Christina M. Ambros-Rudolph and her colleagues suggest the heightened risk may be because marathon runners experience greater exposure to ultraviolet rays, and sweat exacerbates the effect by sensitising the skin to UV rays.
Marathon running has become increasingly popular in recent years and while regular exercise is associated with improved health, some evidence suggests that endurance exercise such as marathon running may be linked to skin cancer and other severe illnesses by suppressing the immune system.
For the study the doctors examined 210 marathon runners after they had treated eight patients with skin cancer, who were all later discovered to be marathon runners.
In almost each case, the cancer had developed on areas not covered by typical running clothing, such as the upper back or lower thigh and calf; the runners were aged 19 to 71, 44 women and 166 men.
When compared with 210 non-runners, the runners had more moles, liver spots and other skin lesions, associated with an increased risk of malignant melanoma and those with the most intensive training regimes had the highest number of moles and liver spots.
After skin examinations, 24 of the runners were referred to specialists with suspected early signs of skin cancer, while only 14 of the control group were referred.
The researchers say marathon runners should be warned 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.
The study is published in the journal the Archives of Dermatology.