Dr John Briffa: Clouded judgment

I can tell we have emerged from the depths of winter by the presence of daffodils and the fact that PR companies have started sending me sunscreen samples along with gloomy statistics about the rising rates of skin cancer in the UK. However, while sunscreen use seems like an obvious way to protect against skin cancer, recent evidence has come to light which has cast a shadow over this practice. Although sunscreens do seem to help prevent the development of a treatable form of skin cancer known as squamous cell carcinoma, two studies have found that their use is associated with a substantially increased risk of the often deadly condition known as malignant melanoma. It seems that using sunscreens to guard against this form of skin cancer may not be such a bright idea after all.

The explanation for this paradox is unknown. One theory is that while sunscreen may help to block out the part of the sun's spectrum that causes burning, its use may prolong exposure to frequencies that are have cancer-causing potential. Another mechanism that helps to explain the link between sunscreen use and increased risk of melanoma concerns vitamin D. This nutrient is made in the body as a result of the action of sunlight on the skin. Some studies show that sunscreen use may reduce vitamin D synthesis, a biochemical effect that may have important implications for health.

Vitamin D has a variety of functions in the body, one of which is to exert a broadly anti-cancer effect. It can dampen the uncontrolledcell growth that is the hallmark of cancer, and helps to induce suicide in cancerous cells. Interestingly, studies have found that vitamin D can inhibit malignant melanoma cells in the test tube. All this raises the question of whether the sub-optimal levels of vitamin D associated with sunscreen use may enhance the potential for melanoma. Indeed, other studies show a link between reduced sunlight exposure and an increased risk of several other types of cancer.

Increasing vitamin D levels through sunlight exposure may do more than reduce our risk of cancer. One study found that raised vitamin D levels induced by light exposure lowered blood pressure to an extent that would be expected to bring meaningful reductions in the risk of heart attacks and strokes. It is essential for the strength and health of bones and muscles, too. While foods and supplements such as sardines, salmon, mackerel and cod liver oil can provide us with useful quantities of vitamin D, ensuring that our skin sees the light of day is the most effective way to maintain optimal vitamin D levels.

Wearing appropriate clothing and taking to the shade are sensible precautions against sunburn, which is believed to age the skin and increase the risk of skin cancer. That said, it is clear that sunlight's ability to boost vitamin D levels mean that its benefits are much more than skin deep.

Thanks to guardian.co.uk who have provided this article. View the original here.