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An inability to tan is the number one risk factor for melanoma. Those who tan easily or who have darker skin are far less likely to develop the disease. A new theory is that melanoma is actually caused by sunlight (vitamin D) deficiency and that safe sun exposure actually helps prevent the deadly disease.
It is commonly believed that exposure to sunlight leads to skin cancer, including deadly melanoma. No one believes this more ardently than leaders of the dermatology profession. For example, a leading dermatologist, Roger Ceilley, MD, has proclaimed, "We're going to have millions more cases of skin cancer in the next decade" if people forgo sunscreen (Fackelmann 1998).
Yet the relationship may not be that simple. There is evidence that a moderate amount of unblocked sunlight is actually beneficial to most people, reducing the risk of many diseases - including, paradoxically, melanoma itself. For example, in often-cited research on US Navy personnel in San Diego, researchers from the University of California School of Medicine found that more melanoma occurred among desk workers than among sailors who worked outdoors (Garland 1990).
Over a ten-year period, 1974-1984, the researchers identified
176 cases of melanoma among active-duty white male Navy personnel. The risk of melanoma was then determined for occupations that were grouped into three categories of sunlight exposure: (1) indoor, (2) outdoor, or (3) indoor and outdoor. Compared with the US civilian population, Navy personnel in indoor occupations had a higher age-adjusted incidence rate of melanoma (10.6 per 100,000). But persons who worked in occupations that required spending time both indoors and outdoors had the lowest rate.
Another intriguing finding was that incidence rates of melanoma were higher on the trunk of the body than on the more commonly sunlight-exposed head and arms. This alone calls into question the notion that exposure to sunlight equals increased rates of melanoma.
The UC San Diego researchers concluded that there was a protective role for brief, regular exposure to sunlight. They also pointed to laboratory studies showing that vitamin D suppresses the growth of malignant melanoma cells in tissue culture. They suggested that vitamin D could inhibit previously initiated melanomas from becoming clinically apparent (Garland1990).
But ideas such as these have made some dermatologists very angry indeed. Boni E. Elewski, MD, current president of the American Academy of Dermatology, has argued that even a few minutes of sunlight exposure can be dangerous, and that people can get all the vitamin D they need through supplements. This is a strange recommendation indeed, since orthodox doctors usually urge the laity to shun food supplements. (Incidentally, I can find no published scientific papers by Dr. Elewski on the topic of vitamin D.)
Despite dermatologists' vehement opposition to the idea, it is not at all clear that small amounts of unblocked sun exposure could be a significant cause of melanoma. As even the Skin Cancer Foundation states, "Epidemiologic studies have suggested that intense intermittent exposure resulting in sunburn, especially in childhood, is most likely to lead to melanoma development." (Skin Cancer Foundation 2004) But full-blown intermittent sunburn is not at all the same thing as getting a bit of sun on a winter afternoon in the northern latitudes.
Of course too much of a good thing can be dangerous. But the essential point that Holick makes is that by moderately increasing our exposure to sunlight, we can probably decrease our risk of many forms of cancer, as well as diabetes, seasonal affective disorder (SAD), multiple sclerosis, and other illnesses. Interested readers should take a look at the maps of disease distribution and mortality at the website of the SUNARC Foundation of San Francisco at http://www.sunarc.org
What these maps clearly show is that, as a general rule, the death rates for breast, colon and ovarian cancer, as well as incidence rates for multiple sclerosis, decrease as one moves south. For example, the breast cancer death rate in the south is about half of what it is in the north and northeast. Dr. William B. Grant, founder of SUNARC, has published a paper in the journal Cancer, in which he argues that these differences are due to sunlight and vitamin D (Grant 2002).If he is correct, then this is very good news indeed for the "worried well."
Brief but regular sunlight exposure could turn out to be a healthful measure that is easy to implement, cost-free and accessible to almost all. And ironically, despite the fervent objections from photophobes in the medical profession, it might even decrease the risk of melanoma.