The health benefits of moderate sun exposure may outweigh the associated skin cancer risks for people who are deficient in Vitamin D, especially those who live in colder northern latitudes, according to a study released Monday.
The study found that Vitamin D levels, which were calculated based on sun exposure, correlated with better survival rates for cancer victims.
People in sunnier, southern latitudes, with higher estimated Vitamin D levels, were significantly less likely to die from their malignancies than people in northern latitudes, according to the paper in the Proceedings of the National Academy of Sciences, (PNAS).
"In previous work, we have shown that survival rates for (prostate, breast, colon and lung) 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," said Richard Setlow, a biophysicist and one of the paper's authors.
"The current data provide a further indication of the beneficial role of sun-induced vitamin D for cancer prognosis."
Vitamin D, dubbed the "sunshine vitamin" because it is produced by the skin from ultraviolet rays, has been shown to have a powerful protective effect against internal cancers, such as breast and colon cancer.
But the emerging evidence on the benefits of the vitamin, and by extension sun exposure, conflicts with longstanding public health messages about the dangers of spending time in the sun because of the risk of developing the potentially deadly skin cancer melanoma.
To explore the pros and cons of time spent in the sun, US and Norwegian researchers analyzed the amount of vitamin D generated by sun exposure at different latitudes and cross referenced it with data showing cancer incidence and cancer survival rates for populations at different latitudes.
They found a clear north-south gradient in vitamin D production, "with people in the northern latitudes producing significantly less than people nearer the equator."
Specifically, they calculated that Australians produce 3.4 times more vitamin D as a result of sun exposure than people in the United Kingdom, and almost five times more vitamin D than Scandinavians.
With respect to major internal cancers such as colon, lung, breast and prostate cancer, they found that while incidence rates increased from north to south, survival rates decreased from north to south.
In other words, while the populations of Australia and New Zealand had higher cancer rates than their counterparts in the United Kingdom, Sweden, Norway and Denmark, they also survived their brush with cancer more often than their northern European "cousins."
This study did not address the question of how the "sunshine" vitamin protects against cancer. Previous studies have suggested it discourages out of control cell reproduction and hinders the formation of new blood vessels for tumours.
Spending time in the sun is not the only way to raise vitamin D levels, Setlow pointed out. People can increase dietary sources of the vitamin, such as cod liver oil or milk, or take vitamin D supplements.
Setlow is a senior biophysicist at the Department of Energy's Brookhaven National Laboratory in Upton, New York, and an expert on the link between solar radiation and skin cancer.
Researchers from the Institute for Cancer Research in Oslo, Norway and the University of Oslo also worked on the paper.