Something as common and available as sunlight may help prevent some lung cancers, researchers say.
A new study finds that lower levels of the sun's ultraviolet B (UVB) rays are associated with a higher incidence of lung cancer across 111 countries.
Still, that doesn't mean that spending more time in the sun will ever offset the risks that come with smoking, according to the study, which is published in the January issue of the Journal of Epidemiology and Community Health.
It's also not an excuse to trade skin cancer for lung cancer.
"The problem is that people might over-interpret this and stay in the sun for hours," said Cedric Garland, study senior author, professor of family and preventive medicine at the University of California, San Diego (UCSD), and participating member at the Moores UCSD Cancer Center in La Jolla.
Too little sun isn't great either, however, since sunlight helps the skin manufacture healthy vitamin D. "It would be false prudence to stay out of the sun to prevent skin cancer and not get enough vitamin D," Garland said.
Other experts, however, feel the focus should stay on cigarette smoking as the number one cause of lung cancer.
"When you have such a strong factor as tobacco, it really weighs out all these other small influences," said Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Health System in Baton Rouge, La. "It's a very interesting observation, but the main message is tobacco is such a strong influence in the development of lung cancer that we should concentrate on that."
More than one million people die of lung cancer worldwide each year. Cigarette smoking causes about 85% of lung cancers. The remaining cases are caused by exposure to secondhand smoke and a variety of other, some unknown, factors.
Sunshine is a significant source of vitamin D, as the sun's UV rays trigger synthesis of vitamin D in the skin.
Previous research, much of it by the same group, has found a strong association between breast cancer, colon cancer and other internal-organ cancers and living in latitudes with less sunlight. For example, one paper observed double the death rate from colon cancer above the U.S. Mason-Dixon line as below, leading the researchers to focus on lack of sunlight as the culprit.
It wasn't a new idea. "There were people in epidemiology dating back to Hippocrates who thought it was a good idea to live on the south side of a hill," Garland said.
Another study linked lower levels of a vitamin D metabolite in the blood with a higher level of colon cancer.
For this study, Garland and his colleagues looked at the association between latitude and exposure to UVB light and rates of lung cancer in 111 countries. Data came from an extensive United Nations database.
Although smoking showed the strongest association with lung cancer, exposure to UVB light also had an impact.
UVB light is greatest closer to the equator. This study showed that lung cancer rates were highest in regions farthest away from the equator and lowest in those regions nearest to it.
Higher cloud cover and aerosol use, both of which absorb UVB rays, were linked with higher rates of lung cancer.
For men, smoking was associated with higher rates of lung cancer, while greater exposure to sunlight was associated with lower rates.
For women, cigarette smoking, along with total cloud cover and aerosol levels, were associated with higher rates of lung cancer, while sunlight was again associated with lower rates.
Previous research has indicated that vitamin D may be able to stop the growth of malignant tumors.
"Everyone should be taking vitamin D, and, at all latitudes, there's plenty of potential to make vitamin D," Garland said. "Even in Helsinki, people can take advantage of the sun in summer months."
And vitamin D produced in the summer will carry over into the winter. Even so, unless you know what your vitamin D levels are, it might be wise to take a supplement, Garland advised.
HealthDay News, December 17, 2007