Skin cancer? Stop beating up your immune system

News that marathon runners and other endurance athletes may be at increased risk of skin cancer shouldn’t have come as a surprise.

Mainstream media focused on the idea that it was increased exposure to the sun that was to blame, and almost universally carried warnings for runners to slap on the sunblock. In doing so they completely missed the point – which is that training and racing suppresses the immune system.

It’s the immune system that controls cancer, not how much sunlight you are exposed to. Distance runners are more likely to develop cancer because they artificially – and chronically -- suppress their immune systems. To add insult to injury, most runners are not nutritionally protected, or at best only partially protected, against the overt stress of protracted exercise.

In the study, scientists at the Medical University of Graz, Austria, evaluated 210 marathon runners -- 166 men and 44 women age 19 to 71. One of their findings was that the marathoners had more atypical moles and "liver spots" than non-runners; higher numbers indicate a greater risk for malignant melanoma. Reading the news reports, you’d think that the researchers had associated the increased number of skin signs with an increased exposure to sunlight. Not at all. What they reported was “These features were more pronounced in those with more intense training regimens”. (My emphasis.)

The scientists actually referred 24 marathoners and 14 non-runners from the control group to dermatologists because they had skin lesions suggestive of non-melanoma skin cancer. Again, they said, “Among the marathon group, there was a higher referral rate among those with the highest training intensity.”

So where exactly is the link with sunshine?

It turns out the scientists have assumed increased exposure because 96.7% of the runners said they wore shorts and short-sleeved or sleeveless 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”, said the Austrian team. They did not measure the runners' actual exposure to sunshine. What's more, it happens that more than half of the runners regularly used sunscreen while training or competing. Only four runners – 1.9% of the total – said they never used sunscreen at all.

So what’s going on here, really?

What marathon runners suffer from is not over-exposure to sunlight, but chronic immune suppression. The more intensely you train and race, the more you should be looking at ways of helping your immune system. Apart from adequate rest and recuperation, an effective way of doing this is to make sure your nutrition is way above average. Taking nutritional supplements designed to help immunity is a must, in my opinion.

The Austrian researchers actually state that it’s the sun-exposure factors “in addition to possible weakening of the immune system caused by extreme training” that may increase athletes' skin cancer risk. Not sun exposure alone. They have focused on UV radiation’s role because they believe it is a factor that is more easily controllable by athletes. But this may change as cancer researchers get to grips with the literature on immune suppression that is rife in sports medicine circles.

Proof that the immune system is the key to combating skin cancer – even malignant melanoma, which is potentially lethal and difficult to treat – has come from two separate studies presented at a European cancer research meeting in Prague this month. Researchers at the University of Louisville, Kentucky, and the University of Southern California, Los Angeles, have shown how using specific drugs in novel ways to boost the immune system resulted in malignant melanomas shrinking and patients remaining alive longer.

We support the recommendation that runners should cover up. But only because we suspect that most runners have inadequate nutrition and we know that they routinely derail their immune systems.

"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."

* Sources: Ambros-Rudolph CM et al. "Malignant Melanoma in Marathon Runners”, Arch Dermatol 2006, 142(11):1471-74. Prague meeting reported in The Guardian (UK), November 10, 2006: “Researchers use body's immune system to fight skin cancer”, by Alok Jha.