For almost as long as I can remember we have been cautioned about the need to avoid excess exposure to sunlight lest it trigger potentially lethal skin cancer, particularly the form known as "malignant melanoma." Yet, for some time there has been evidence amassing that sunlight exposure is also associated with a decreased risk of several other cancers including those of the breast, prostate, and colon. Others and I have argued for some time that because internal cancers are far more common than malignant melanoma, then shying away from the sun is likely to do more harm than good with regard to overall cancer risk. And, earlier this month, someone did some number crunching and appears to have also found this.
Johan Moan and fellow researchers from the Institute for Cancer Research in Oslo, Norway, have published a paper, which dissects the relationship between sunlight exposure and cancer risk. In their analysis, published in the Proceedings of the National Academy of Sciences [1], they assume that increased sunlight exposure increases the risk of malignant melanoma. I say, assume because, as the authors agree, the link is far from established. In fact, several lines of evidence suggest that sunlight exposure is not the potent force in the development of melanoma that it is so often said to be. OK, but let's err on the side of safety and go with the idea that sun exposure does definitely increase melanoma risk.
Against this, as I mentioned earlier, it is necessary to take into consideration the data which shows that sunlight exposure reduces the risk of several major internal cancers. This is partly evidenced by the fact that at lower (sunnier) latitudes, cancer incidence is lower than it is at higher latitudes. We also know that sunlight exposure increases vitamin D production in the skin and that this nutrient is known to have anti-cancer properties. Once all cancers are taken into consideration, the data in the Proceedings of the National Academy of Sciences' study support the idea that: "Increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse effects on health."
In a report on this study from Reuters, it is claimed that Johan Moan has calculated that if Norwegians doubled their sunlight exposure, the number of annual deaths from skin cancer would rise by 300 (remember, that's only if we assume sunlight does actually cause melanoma), but that annual deaths from other forms of cancer would fall by 3,000. In light of this, the idea that "increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse effects on health" does seem conservative to me. And it seems even more conservative when one considers that sunlight exposure and enhanced vitamin D levels may not only reduce overall cancer risk, but also the risk of several other conditions, including cardiovascular disease.
References:
1. Moan J., et al. Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. Proceedings of the National Academy of Sciences 2008; 105(2): 668-673
Dr. John Briffa is a London-based doctor and author with an interest in nutrition and natural medicine.
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