Is the sun good or bad for your health? A new research made at the U.S. Department of Energy, Brookhaven National Laboratory, and published in the "Proceedings of the National Academy of Sciences" points that what you gain with moderately increased exposure to sunlight (i.e. vitamin D, involved in preventing cancers and other illnesses), could overcome the risk of skin cancer in the case of people who have a deficiency in this vitamin.
"We know that solar radiation is the leading cause of skin cancer", said lead author Richard Setlow, a Senior Biophysicist Emeritus at Brookhaven.
His team has discovered for the first time that ultraviolet A (UVA) radiation and visible light are the main factors inducing malignant melanoma, the most severe type of skin cancer. But sunlight is at the same time a major, if not the first, source of vitamin D in humans, transforming precursor fatty molecules into the active vitamin.
"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. The concern is particularly great in populations from northern latitudes, such as Scandinavia, where sun exposure is extremely limited", said Setlow.
The team employed a model using data on sun radiation intensity and a vertical cylinder shape (mimicking the human body's skin surface and more realistic than flat surface exposures employed in previous researches) to assess the amount of synthesized vitamin D, depending on latitude.
Australians (close to the Equator) were found to synthesize 3.4 times more vitamin D than British, and 4.8 times more than Scandinavian people.
"There is a clear north-south gradient in vitamin D production, with people in the northern latitudes producing significantly less than people nearer the equator", said Setlow.
In the case of people with similar skin tones, there was a gradual increase in the incidence of all types of skin cancer from north to south.
"This gradient in skin cancer rates indicates that there is a true north-south gradient in real sun exposure", said Setlow.
The rates of main internal cancers like colon cancer, lung cancer, breast cancer and prostate cancer also got higher from north to south. But, the survival rates in these cases were much higher in the case of southern people.
"In previous work, we have shown that survival rates for these cancers improve when the diagnosis coincides with the season of maximum sun exposure, indicating a positive role for sun-induced vitamin D in prognosis - or at least that a good vitamin-D status is advantageous when combined with standard cancer therapies. The current data provide a further indication of the beneficial role of sun-induced vitamin D for cancer prognosis. As far as skin cancer goes, we need to be most worried about melanoma, a serious disease with significant mortality", said Setlow.
Melanoma is caused by the long UVA and visible light, while vitamin D synthesis is produced by the short UVB.
"So perhaps we should redesign sunscreens so they don't screen out as much UVB while still protecting us from the melanoma-inducing UVA and visible light. Increased UVB exposure may result in an increase in non-melanoma skin cancers. But these are relatively easy to cure and have very low mortality rates compared with the internal cancers vitamin D appears to protect against", said Setlow.
Dietary sources of vitamin D are cod liver oil, milk, dairy products, eggs and others.