Vitamin D May Lower Some Cancer Risk
Benefits Seen for Breast, Colon, and Ovarian Cancer
Intriguing, but Not Conclusive
In their latest analysis, Garland and colleagues conducted a comprehensive review of observational studies evaluating vitamin D status in relation to cancer risk. The analysis involved 63 studies conducted between 1966 and 2004, and many examined sun exposure as a measure of vitamin D levels.
Of the 30 colon cancer studies, 20 found a significant benefit for vitamin D levels, sunlight exposure, or another marker of vitamin D status on cancer risk or death and occurrence of precancerous polyps. Nine of 13 breast cancer studies showed an associated benefit; five of seven ovarian cancer studies found higher death rates associated with lower sun exposure or decreased vitamin D intake.
Twenty-six studies examined the role of vitamin D or sunlight exposure on prostate cancer, but the findings were mixed; 13 studies showed a benefit and 11 studies showed no significant association.
American Cancer Society (ACS) epidemiologist Marji McCullough, ScD, RD, says the evidence suggesting a protective role for vitamin D against certain cancers is growing, but it is not yet conclusive.
"The studies are intriguing, and this question certainly deserves further study and more rigorous evaluation," she tells WebMD.
She adds that the ACS is reviewing its guidelines on nutrition and cancer risk, as it does every five years, and the new research on vitamin D is being examined.
Sun Exposure Revisited
Most multivitamins now contain 400 IU of vitamin D, and Garland says the hope is that manufacturers will soon increase this dosage to 1,000 IU. He adds that milk and vitamin-D- fortified yogurt and cheese are good dietary choices because they also have calcium.
But an 8-ounce glass of milk contains only 100 IU of vitamin D. By comparison, someone who spends 10 to 15 minutes in the sun on a sunny day without sunscreen can absorb 2,000 to 5,000 IU of vitamin D if 40% of the body is exposed, he says.
"The reality is that oral intake cannot compete with the amount of vitamin D that can be synthesized from sun exposure," he says. This must be balanced with the concern for risk of skin cancer.
Garland says health officials are beginning to accept the message that limited sun exposure may be a good thing.
While supplements and foods are the only choice for people who cannot tolerate the sun, he says most people can safely spend 10 to 15 minutes in the sun each day. If they are out in the sun any longer, he says, they should put on sunscreen.