I am a big believer in the therapeutic properties of sunlight, at least some of which is related to its ability to stimulate vitamin D production in the skin. Sunlight exposure and/or heightened vitamin D levels have been associated with a range of health benefits including a reduced risk of several forms of cancer and relative protection from multiple sclerosis. I was therefore interested to read over the weekend an editorial in the British Medical Journal which highlights the importance of sunlight and vitamin D in health.
Written by Professor Michael Holick (professor of medicine, physiology and biophysics at Boston University Medical Centre in Boston, USA), the editorial details some of the evidence for the benefits of sunlight exposure and/or vitamin D including their role in bone and muscular health (vitamin D deficiency can lead to bone disease and muscular fatigue and pain). Not surprisingly, Michael Holick’s editorial mentions cancer too.
When the words ‘sunlight’ and ‘cancer’ are heard together, it’s natural for our thoughts to turn to skin cancer. There are three main forms of skin cancer: what are known as ‘squamus cell carcinoma’ and ‘basal cell carcinoma’, and ‘malignant melanoma’. The first two tend to develop on the most sun-exposed parts of the body (e.g. the top of the ear) and are generally very treatable. Malignant melanoma, on the other hand, is generally much less treatable, is quite often deadly, and is usually the major reason cited regarding why we should protect ourselves from the sun.
However, is the relationship between sunlight exposure and risk of malignant melanoma as clear-cut as we are generally led to believe it to be? Michael Holick’s editorial contains information that might cause us to question traditional wisdom on this. He writes: Notably, non-melanoma skin cancers occur on the most sun exposed areas, such as the face and hands, whereas most melanomas occur on the areas least exposed to the sun [2]. Intermittent and occupational sun exposure has been found to reduce the risk of malignant melanoma [2-5].
In short, Professor Holick appears to be asking: “If sunlight exposure causes malignant melanoma, how come it tends to develop on parts of the body that are not typically very sun-exposed, and how come there is evidence linking sun-exposure with reduced risk of this condition?” Professor Holick appears to cast considerable doubt on the notion that excessive exposure to sunlight is a major risk factor for malignant melanoma.
Even if it is, I still think it’s worth bearing in mind all the benefits that may come from sunlight that may offset any downside. For more on this, see this previous post. And for more advice on safe-tanning and natural sun-protection, see here.
References:
1. Holick M. Deficiency of sunlight and vitamin D. BMJ 2008;336:1318-1319
2. Kennedy C, et al. The influence of painful sunburns and lifetime of sun exposure on the risk of actinic keratoses, seborrheic warts, melanocytic nevi, atypical nevi and skin cancer. J Invest Dermatol 2003;120:1087-93
3. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81
4. Grant WB, et al. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res 2006;26:2687-99
5. Moan J, et al. Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. Proc Natl Acad Sci 2008;105:668-73
