Women in Sunnier Countries Have Lower Ovarian Cancer Rates

The risk of developing ovarian cancer is 60 percent lower among women living in areas of the world with high ultraviolet B radiation exposure than those who live in areas with less UVB, concludes a study encompassing 175 countries.

"The main reason for this advantage is that women living in sunny areas have higher circulating (vitamin D2) levels that protect them from ovarian cancer," said lead researcher Dr. Cedric Garland, a professor of family and preventive medicine at the University of California in San Diego.

Exposure to UVB from sunlight allows skin to photosynthesize vitamin D, which enters the bloodstream and circulates throughout the body.

For the study in the latest issue of the American Journal of Preventive Medicine, the researchers correlated 2002 data on UVB radiation, stratospheric ozone measurements and fertility rates of young women with incidence rates of ovarian cancer worldwide.

They found that ovarian cancer incidence rates were highest in countries in northern latitudes, the countries with less annual sunlight. Levels of UVB radiation and fertility rates of women age 15 to 19 were higher where the incidence of ovarian cancer was lower.

Higher levels of stratospheric ozone, which reduces transmission of UVB, correlated with higher rates of ovarian cancer.

The authors said that a geographical difference in mortality rates of ovarian cancer had previously been seen in the United States, with the highest rates in the Northeast and lowest in the South and Southwest.

This suggested to them that lower levels of solar radiation might be associated with increased risk of ovarian cancer, and that "previous laboratory findings also suggest that low levels of vitamin D metabolites" could play a role in causing the disease.

"This is a very important observation that confirms the previous observations by these authors and others that vitamin D deficiency increases risk of many deadly cancers that now includes ovarian cancer," said Dr. Michael Holick, a professor of medicine, physiology and dermatology at Boston University School of Medicine.

The authors also say that the correlation of UVB radiation to ovarian cancer has been shown to be similar to that of colon cancer, suggesting that the protective role of vitamin D in ovarian cancer prevention could be similar to its established role in colon cancer prevention.

Both women and men should be screened every five years vitamin D levels in the blood, Garland said. "This simple blood test should be done in January or February in the northern hemisphere, July and August in the southern."

"Almost all vitamin D in circulation in most people originates from brief exposures of skin to the sun," he added. "Spending 15 to 20 minutes per day in the sun around noon daily could result in similar reductions in risk of ovarian cancer."

Garland C, et al. Role of ultraviolet irradiance and vitamin D in prevention of ovarian cancer. Am J Prev Med 31(6), 2006.

By Health Behavior News Service