For almost as long as I can remember, we have been cautioned about the need to avoid excess sunlight exposure lest it trigger potentially lethal skin cancer, particularly what is known as ‘malignant melanoma’. Yet, there as for some time been amassing evidence that sunlight exposure is also associated with a decreased risk of several other ‘internal’ cancers including those of the breast, prostate and colon. I and others have argued for some time that because internal cancers are way 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 this week, someone did some number-crunching and appears to have found exactly 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 sunlight increased sunlight exposure increases the risk of malignant melanoma. I say ‘assume’ as, as the authors agree, this 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 it is so often said to be. OK, let’s err on the side of safety though, 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 show 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 at higher latitudes. We also know that sunlight exposure increases vitamin D production in the skin, and this nutrient is known to have anti-cancer properties. Once all cancers are taken into consideration, the data in the PNAS study support the idea that, in the words of the study authors: “increased sun exposure may lead to improved cancer prognosis and, possible, 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 assuming sunlight does cause melanoma), but that annual deaths from other forms of cancer would fall by 3000. In light of this, the idea that ‘increased sun exposure may lead to improved cancer prognosis and, possible, give more positive than adverse effects on health’ does seem highly conservative to me. And it seems even more conservative when one considers that sunlight exposure and enhanced vitamin D levels may not just reduced overall cancer risk, but the risk of several other conditions too including cardiovascular disease.
By way of example, let me share with you the results of another study published this week, that assessed the relationship between vitamin D levels and risk of ‘cardiovascular events’ such as heart attack and stroke [2], This study, which focused on an American population, found that individuals with blood vitamin D levels less than 15 ng/mL were, compared to those with higher vitamin D levels, at a 62 per cent increased risk of cardiovascular disease as assessed over an average of more than 5 years. This increased risk appeared to be confined to people with raised blood pressure. Taking these people on their own, those with lower vitamin D levels were found to be at more than twice the risk of cardiovascular disease. These associations were found even when other factors that at traditionally thought to affect cardiovascular risk (such as physical activity) were accounted for.
And let’s not forget that vitamin D is believed to help protect against other conditions such as osteoporosis, rickets and multiple sclerosis.
Add this to the cancer data just out and there is, I think, overwhelming and compelling evidence to suggest that sunlight exposure is, by and large, a good thing. As I’ve said before, we probably don’t want to be allowing our skin to burn, but with that caveat in place, increased sun exposure looks like it has the capacity to save lives. Lots of ’em. The authors of the PNAS piece allude to this when they say in their paper that: “Authorities should pay attention not only to skin cancer research, but also to research on vitamin D-sun-health relationships”.
Thinking about the wider implications of all this for a moment, I think there is reasonable grounds for suspecting that all this ‘anti-sun’ propaganda we’ve been subjected to will or already has lead to a significant increase in morbidity (ill-health) and mortality. And why? Well, as I’ve pointed out before, one factor here is likely to be the fact that there’s money in sun protection, while sun exposure is essentially free. Though I don’t suppose this is the only example of where an industry might have put profit before people.
References:
1. Moan T, et al. Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. PNAS 2008;105(2):668-673
2. Wang TJ, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation 2008 [epub before print on 7th January 2008]
