The Lancet, Volume 376, Issue 9736, Page 142, 17 July 2010
doi:10.1016/S0140-6736(10)61094-XCite or Link Using DOI
The public health message is compellingly simple: avoid the sun to prevent melanoma and other forms of skin cancer. Unfortunately, exposure to sunlight is the mainstay of vitamin D synthesis, and vitamin D deficiency causes rickets and osteomalacia, contributes to osteoporosis, and has been associated with many other disorders, including diabetes, cancer, and cardiovascular disease.
Ultraviolet B radiation produces 90% of vitamin D in human beings; only a very small proportion can be obtained through diet. However, at high latitudes, levels of sunlight in winter are often so low that vitamin D insufficiency is common. Avoidance of the sun's rays by covering up or use of sunscreen can compound this problem, and is thought to have contributed to a recent increase in metabolic bone disease. Cancer Research UK recognises the need to balance skin cancer prevention with generation of adequate vitamin D, but specified that “the skin efficiently produces vitamin D at levels of sun exposure below those that cause sunburn…when it comes to sun exposure, little and often is best”. Australia's SunSmart guidelines http://www.cancer.org.au/cancersmartlifestyle/SunSmart/VitaminD.htm underwent a revision to reflect this balance in 2006—07.
A major concern is that people might seek prolonged sun exposure without protection to boost vitamin D synthesis. Indeed, the American Academy of Dermatology argues that the risks of sun exposure outweigh the benefits, advocating instead for dietary supplementation as a safe source of vitamin D. A report published in the British Journal of Nutrition http://dx.doi.org/10.1017/S0007114510002436 (400 IU is not enough for pregnant mothers) emphasises that in the UK, a unified approach to vitamin D supplementation is needed to address deficiency in pregnant women and avoid life-threatening complications for their babies.
Despite the simmering debate about sun exposure surrounding vitamin D, the SUNLIGHT consortium's genome-wide association study, published in The Lancet today, should add to our understanding of the genetic basis of interindividual variability in the synthesis of vitamin D. These findings could eventually help to identify who is most at risk of vitamin D insufficiency and related diseases. Until such potential applications come to the fore, the message about sun exposure has to be sensibly moderate. Enjoy the summer sun, with caution.