Lack of Sunlight Found to Greatly Increase Risk of Lung Cancer

A new study has found a correlation between higher rates of lung cancer and less exposure to sunlight.

The study was conducted by researchers from the University of California at San Diego and published in the Journal of Epidemiology and Community Health. Researchers examined data from national and international databases, including those from the World Health Organization, to compare lung cancer rates in 111 different countries. The researchers searched for correlations with national rates of smoking, as well as latitude, high cloud cover and levels of airborne aerosols.

A lower latitude indicates more sunlight and hence more exposure to the UVB radiation that causes the body to synthesize vitamin D. UVB is blocked by high cloud cover and airborne aerosols, so those factors indicate lower exposure.

The researchers found that the strongest correlation with lung cancer rates came from smoking, which was responsible for between 75 and 85 percent of all cases. But they also found a significant correlation with lower UVB exposure.

Among men, cancer rates were higher the farther a man lived from the equator. Among women, cancer rates increased with distance from the equator, high cloud cover and airborne aerosols. These correlations remained even after adjusting for the effects of smoking.

Lung cancer is one of the three most common cancers among men and women in developed countries. It kills more than one million people each year.

Researchers believe that sunlight helps protect against cancer by stimulating the production of vitamin D. Lead researcher Cedric Garland said that vitamin D is believed to cause the body to release chemicals that combine with calcium to cause the cells in organ linings to stick more closely together. This prevents these cells, which appear to be most vulnerable to cancer, from dividing uncontrollably.

While the current study looked only at lung cancer, prior studies have found that living far from the equator results in a higher risk of other internal organ cancers, such as colon cancer and breast cancer. One study found that people who live north of the Mason-Dixon Line in the United States died of colon cancer at twice the rate of those living south of it. Another study looked at vitamin D directly and found that lower blood levels of vitamin D metabolites correlated with a higher risk of colon cancer.

“The problem is that people might over-interpret this and stay in the sun for hours,” Garland said. Moderation, he emphasized, is the way to go. “It would be false prudence to stay out of the sun to prevent skin cancer and not get enough vitamin D.”

Kat Arney of Cancer Research U.K. agreed. “The time in the sun needed to get enough vitamin D is much less than the time it takes to tan or burn.”

Garland recommends spending five to 15 minutes in the sun every day that weather permits. This presumes that this takes place on a mostly clear day, approximately 40 percent of skin area is exposed and that exposure takes place within two hours of midday. Having more skin covered, being out at a different time or a less clear day would increase the time needed. People should wear wide-brimmed hats if exposure will be longer than a few minutes, but should not use sunscreen, which blocks vitamin D synthesis.

Garland emphasized that moderate sunlight exposure does not significantly raise a persons risk of melanoma, the most dangerous form of skin cancer.

“Theres plenty of potential to make vitamin D,” Garland said. “Even in Helsinki, people can take advantage of the sun in summer months.”

Vitamin D produced by the body during the summer can be stored until the winter.