It has been the common wisdom for decades and the mantra of the pale and pasty who would rather not get hot and bothered: stay out of the sun to avoid getting skin cancer. If you must go out, slap on the sunscreen or cover up.
But that advice might need some reconsideration: a study suggests that the health benefits of vitamin D, which is produced by the skin when it is exposed to sunshine, could justify a modest increase in the amount of time we spend in the sun. "Since vitamin D has been shown to play a protective role in a number of internal cancers and possibly a range of other diseases, it is important to study the relative risks to determine whether advice to avoid sun exposure may be causing more harm than good in some populations," said Richard Setlow, a biophysicist at the Brookhaven National Laboratory in the US and an expert on the link between solar radiation and skin cancer.
His study, published yesterday in the Proceedings of the National Academy of Sciences, showed that people with higher levels of vitamin D were more likely to survive cancers such as those of the colon, breast and lung. "Increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse health effects," wrote the researchers.
The finding adds to a growing body of evidence that, in addition to maintaining healthy bones, vitamin D can protect against a range of ailments from colon, lung and ovarian cancers to cardiovascular disease and boost immune function. But concerns over skin cancer and a lack of vitamin D in our diets mean that people may not be getting the full benefits of the nutrient. Ed Yong, a health information manager at Cancer Research UK, said that the study was not at odds with messages to stay safe in the sun.
"It's becoming increasingly clear that vitamin D does have some benefits in terms of reducing people's risks of cancer. [But] the amount of sun exposure it takes to produce enough vitamin D is always less than the amount it takes to tan or burn. There should always be an achievable balance between getting enough vitamin D to reduce your risk of [cancer], while not getting enough sun exposure to tan or burn and thus increase your risk of skin cancer."
Graham Bentham, an environmental scientist at the University of East Anglia, said there was clear evidence that a large proportion of the UK population were not getting enough vitamin D. Experts recommend 5 to 25 micrograms of the vitamin a day but around 90% of adults in the UK get less than three.
"It's probable this is getting worse rather than better because of modern lifestyles - things like a switch amongst kids from outdoor physical activity to more indoor leisure pursuits [and] people being more concerned about exposure to sunlight causing skin cancer."
Yong said that CRUK's advice had always been about sensible amounts of sun exposure, rather than avoiding sunshine altogether. "First and foremost we tell people to avoid sunburn - that has been conclusively shown to double the risk of skin cancer."
Malignant melanoma, the most aggressive form of skin cancer, is notoriously difficult to treat. The average life expectancy for someone with melanoma is around nine months, and less than 20% of patients survive more than two years after diagnosis. It is the cancer that occurs most rapidly, especially among the young - almost 9,000 new cases are diagnosed every year with 1,777 deaths from the disease in 2004.
To get the benefits of vitamin D without increasing the risk of melanoma, Setlow suggested that perhaps sunscreens could be re-designed to filter out the cancer-causing UVA rays and let through only the vitamin-D-producing UVB rays. He admitted increased exposure to UVB rays could increase non-melanoma skin cancers, but said these were relatively easy to treat.
Another option, said Setlow, might be to continue using sunscreens but to increase vitamin D intake through foods such as milk, fish, cod liver oil and some fortified cereals.
In his study Setlow worked with colleagues at the Institute for Cancer Research in Oslo to model how much sunshine a person might get depending on the latitude on which they lived, and the incidence and survival rates for various forms of internal cancers in people living at different latitudes.
Their calculations showed that people living in Australia produce 3.4 times more vitamin D as a result of sun exposure than people in the UK, and 4.8 times more than people in Scandinavia.
The study also revealed that the incidence of major cancers such as those of the colon, lung and breast also increased from north to south; but people in southern latitudes were significantly less likely to die from these cancers than people in the north.
In a separate study published yesterday in the journal Circulation, scientists at the Harvard Medical School in Boston found that a deficiency of vitamin D increased people's risk of developing cardiovascular disease.
Scientists looked at 1,739 patients, all sons and daughters of the original participants of the Framingham Heart Study, a major investigation of heart disease risk factors launched in 1948.
Explainer: Vitamin D