There is growing evidence that vitamin D helps protect against colorectal cancer, and now a group of researchers who have long studied the vitamin say the same is true for breast cancer and ovarian cancer.

In a new analysis, the researchers contend that taking 1,000 international units (IU) of vitamin D daily can cut colon, breast, and ovarian cancer risk.

Cancer Prevention: What Really Works?

The researchers urged public health officials to increase recommendations for vitamin D consumption, calling the vitamin an inexpensive tool for preventing cancers that claim millions of lives each year.

The easiest way for the body to get vitamin D is through sun exposure, because UV rays from the sun trigger the natural synthesis of the vitamin in the body. But the researchers did not address sun exposure in their analysis, focusing instead on the message that people need to get more vitamin D through the foods they eat and vitamin supplements.

Vitamin D Recommendations

Current recommendations call for people between the ages of 1 and 50 to consume 200 IU of vitamin D daily, with 400 IU recommended for those between the ages of 51 and 70. After age 70, 600 IU of vitamin D are recommended each day.

"The cost of a daily (1,000 IU) dose of vitamin D3 is less than 5 cents, which could be balanced against the high human and economic costs of treating cancer attributable to insufficiency of vitamin D," the researchers write in the February 2006 issue of the American Journal of Public Health.

Special Report: A Closer Look at Cancer

Researcher Cedric Garland, DrPH, of the University of California, San Diego, has been studying the impact of vitamin D on cancer since the 1980s. He says the evidence now suggests that vitamin D deficiency is responsible for several thousand premature deaths each year from colon, breast, and ovarian cancer.

"There have now been more than 1,000 studies examining vitamin D and cancer," he tells WebMD. "It has been a slow process, but I do believe that health officials are beginning to embrace our message."

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.

Anticancer Agent in Veggies Shows Promise

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.

How to Keep Your Veggies Vitamin-Packed

"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.

Visit WebMD's Cancer Health Center

Written by Salynn Boyles. Reviewed by Louise Chang, MD.

SOURCES: Garland, C.F. American Journal of Public Health, February 2006, vol 96: pp 9-18. Cedric F. Garland, DrPH, professor, department of family and preventive medicine, University of California, San Diego. Marji McCullough, ScD, RD, nutritional epidemiologist, American Cancer Society. National Academy of Sciences.