Alert to marathon runners: While you're spending all that time building up your heart and lungs, you may also be building up skin damage that could come back to haunt you. A new study from dermatologists at the Medical University of Graz in Austria shows that marathoners have an increased risk of developing melanoma, the most dangerous skin cancer.

The researchers studied 210 white male and female marathoners aged 19 to 71, comparing their melanoma risks against 210 age - and gender-matched white men and women who were not distance runners. All were given total-body skin exams and surveyed about their personal and family skin cancer histories, sunburn histories, sun sensitivity, traits such as eye color and skin type, and any changes in moles.

Although more non-runners by chance had light-colored eyes, fair skin and higher sun sensitivity, the runners had more "atypical" moles (usually large, asymmetrical, irregularly bordered moles with varied colors), more lesions suggestive of basal and squamous cell carcinoma, and more solar lentigines — so-called "age spots" or "liver spots" that really result from sun damage. All of these are risk factors for melanoma.

"Most runners trained 25 to 45 miles a week, and almost 15 percent ran more than 45," said lead researcher Christina M. Ambros-Rudolph, MD. "The more miles they put in, the more skin lesions they had."

The most obvious reason for their increased risk, she noted, was their excessive exposure to the sun's ultraviolet rays. Many worsened the problem by neglecting sun protection. Almost all tended to wear shorts and short-sleeved or sleeveless shirts, leaving their legs, arms, and upper back sun-exposed. Only 56 percent regularly used sunscreen. The researchers also pointed to another factor in the runners' increased melanoma risk: depleted immunity from all the high-intensity exercise, which may have left them more vulnerable to skin damage. "I believe that this will prove to be the key factor," said Arnold W. Klein, MD, professor of medicine/dermatology at UCLA's David Geffen School of Medicine. "Intensive exercise makes them nutritionally depleted, compromising their immune system."

"While marathon running is perceived as healthy, suppressed immunity and sun damage are associated with medical risks," concluded Dr. Ambros-Rudolph. "Runners must take greater precautions, above all choosing training and competition schedules with lower sun exposure, wearing adequate clothing, and regularly using sweat-resistant, high-SPF sunscreens."

Sun Protection Tips for Runners

• Run during hours when the sun is less intense. Generally it is strongest between 10 a.m. and 4 p.m. If you train during those hours, find shady places to run.
• Put sunscreen on before your running outfit, not at the race site. This will give it time to soak in, and keep you from applying it less thoroughly or forgetting it altogether because of pre-race excitement.  Use an SPF 15 or higher sunscreen.  Look for stick formulations, sport, or water-resistant versions.
• Run in a hat and UV-blocking sunglasses. Polarized lenses help beat the glare.
• Always keep sunscreen in your race bag.
• Have a friend posted somewhere in the second half of the race to hand you a small, one-use, wipe sunscreen (or keep a small packet in your pocket), so that you can reapply it to your face, neck and arms as you run. You can do that without really breaking stride. Sunscreen starts to lose effectiveness at about the two-hour mark, or even sooner if you are sweating heavily.
• Before post-race festivities begin, reapply sunscreen, and give yourself a quick massage in the process to help relax your sore muscles.
• Post-race clothes should include a lightweight but long-sleeve T-shirt and sweats. Darker colors offer ideal sun protection. Or opt for special sun-protective clothing.