Women in the sunnier regions of the world have a much lower risk of ovarian cancer than those who dwell in colder climates, a new study has found.
The findings, say researchers, suggest that sun exposure — and, more precisely, vitamin D production in the body — help prevent this cancer.
The study, which appears in the December issue of the American Journal of Preventive Medicine, is the latest to tie latitude to cancer risk. Others have found that rates of breast cancer and colon cancer, for example, are higher among people living in higher latitudes, where annual sun exposure is limited.
The theory is that vitamin D explains the link. Sunlight triggers vitamin D synthesis in the skin, so a person’s stores of the vitamin depend, in part, on where he or she lives. Moreover, a growing number of studies have linked vitamin D intake and vitamin D levels in the blood to cancer risk.
One recent study found that adults who took 400 IU of vitamin D per day were half as likely as people who took no vitamin D supplements to develop pancreatic cancer.
Lab research has also shown that the vitamin helps thwart cancer cell growth and proliferation.
It’s particularly important to find ways to lower ovarian cancer risk because there’s no good way to detect it early, said Dr. Cedric F. Garland of the University of California San Diego, the lead author of the new study.
To investigate the possible role of sun exposure in ovarian cancer, he and his colleagues examined data on ovarian cancer rates in 175 countries and correlated it with information on latitude, UV radiation and atmospheric levels of ozone — which affects UV transmission.
Overall, Garland’s team found, ovarian cancer rates were highest in higher-latitude regions in both hemispheres. In addition, greater UV exposure and lower ozone levels were both linked to lower ovarian cancer rates.
The findings show only an association between latitude and ovarian cancer, and not that vitamin D fights the disease. Many other factors, from genes to lifestyle habits to reproductive choices, differ among women living in low- and high-latitude nations — with countries farther from the equator being more developed and affluent in general.
And no one is recommending that women bask in the sun, or move to Florida, to prevent ovarian cancer, Garland said. “We don’t want anyone to burn,” he advised.
However, the body of evidence on cancer and vitamin D suggests that modest sun exposure and use of vitamin D supplements could offer a cancer defense, according to the researcher.
A person with medium-tone skin, he said, could get enough vitamin D by spending about 15 minutes in the sun each day, with 50 percent of the skin exposed — less time for a fair-skinned person, more for someone with dark skin.
But since many people get little sun, Garland recommended that adults take 2,000 IU of vitamin D a day, which is the “tolerable upper intake level” set by U.S. health officials.
That limit exists because of the risk of vitamin D toxicity, which causes elevated calcium levels in the blood and problems such as nausea, weight loss, fatigue and kidney dysfunction.