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Vitamin D May Protect Against Cancer

Researchers Say Supplements May Help Cut Risk of Breast, Colon Tumors

Sun Exposure and Diet

In a separate study, Julia A. Knight, PhD, of the Mount Sinai Hospital in Toronto, and colleagues conducted telephone interviews with 576 women who had been diagnosed with breast cancer and about 1,000 women without cancer. The women, aged 20 to 59, were asked about sun exposure and diet throughout their lives.

Ever working in a job outdoors, thereby exposing women to sunlight, resulted in an estimated 40% reduced risk of breast cancer for women, while frequent outdoor activities between ages 10 to 29 lowered breast cancer risk by an estimated 35%.

Also, taking vitamin D-rich cod liver oil between ages 10 to 19 reduced breast cancer risk by about 35%, and consuming at least nine glasses of milk every week between the ages of 10 to 29 reduced the risk by 25%.

"Current thinking is that exposures during adolescence or before a full-term pregnancy may have a greater effect, as that is when breast tissue is going through the most rapid development," Knight tells WebMD.

High Intake Protects Men, Too

The third study, which appears in the current issue of the Journal of the National Cancer Institute, examined the association between vitamin D and cancer among 47,800 men in the Health Professionals Follow-up Study.

Between 1986 and 2000, 4,286 of the men developed cancer and 2,025 of them died from it. According to Harvard researcher Edward Giovannucci, MD, ScD, men whose vitamin D levels reflected an increased increment (that could be provided by at least 1,500 IU daily) were 17% less likely to develop cancer and 29% less likely to die of the disease.

High levels of vitamin D were particularly protective against digestive system cancers (which includes colon cancer), with 1,500 IU daily associated with a 43% reduction in risk of developing such tumors and a 45% lower risk of dying of them.

William G. Nelson, MD, PhD, of Johns Hopkins University, says he agrees that men and women should get at least 1,000 IU of vitamin D a day.

"Higher amounts may eventually prove better, but for now that amount is likely to be safe and have a protective effect," he tells WebMD.

Nelson moderated a news conference to discuss the findings.

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