Vitamin D appears effective in reducing Colorectal Cancer incidence

By Valerie DeBenedette, Contributing Writer
Health Behavior News Service

A larger daily dose of vitamin D could reduce the incidence of colorectal cancer with minimal risk, according to a new review that pools results from five studies.

The analysis found that maintaining a specific target blood level of vitamin D was associated with a 50 percent lower risk of colorectal cancer than that seen in people with consistently lower blood levels.

Previous studies had shown that lower blood levels of vitamin D did not protect against colorectal cancer, according to lead author Edward Gorham, Ph.D., a research epidemiologist with the Naval Health Research Center in San Diego. However, a meta-analysis pools the data from several studies, thus increasing the strength of the results.

The study is being published in the March issue of the American Journal of Preventive Medicine.

The five studies looked at serum collected from healthy volunteers who were then followed for periods ranging from two years to 25 years. There were 535 cases in the pooled analysis and 913 controls, or 1,448 total participants.

The researchers found that a blood serum vitamin D level of 33 nanograms per milliliter or higher was associated with a 50 percent lower risk of colorectal cancer than that seen with blood levels of 12 nanograms per milliliter or lower.

Vitamin D levels in the body are a factor of both diet and sun exposure. Exposing the skin to the sun lets the body synthesize vitamin D, which is why mortality due to colorectal cancer may be higher in geographic areas that get less sunshine.

The amount of dietary vitamin D needed to reach the serum levels that appear to be protective against colorectal cancer — 1,000 to 2,000 international units a day — would not pose any risk, according to Gorham: “The Institute of Medicine has set a ‘No Adverse Effect Level’ of 2,000 IU per day for vitamin D intake, so this recommendation would be safe for most people.”

There is no official recommended dietary allowance for vitamin D, but an adequate dietary intake per day for most adults is currently considered to be 200 to 400 IU.

Small amounts of sun exposure would also help people boost their vitamin D levels. Fifteen to 20 minutes per day without sunscreen is enough for the body to synthesize 10,000 IU of vitamin D with minimal risk of sunburn or skin cancer, Gorham said.

“The results are pretty straightforward,” said Karen Glanz, Ph.D., director of Emory University’s Prevention Research Center at the Rollins School of Public Health. However, changing behavior on the basis of this study may be premature, she said. The analysis found an association between vitamin D levels and lowered risk, not a definite link, Glanz said, but adding vitamin D to the diet or taking a supplement would probably not do much harm and there could be a benefit.