Vitamin D Could Lower Cancer Risk

Recent data suggest that vitamin D supplementation could reduce the risk of developing deadly or metastatic cancer.

Published in JAMA Network Open, the study involved 25,000 men and women who were assigned either a placebo or 2,000 international units (IU) of vitamin D a day for about five years. Those receiving vitamin D were 20% less likely to develop an advanced cancer.

The authors noted, however, there was no benefit in people who were overweight or obese. The study researchers reviewed a previous randomized trial of 26,000 cancer-free participants known as VITAL (Vitamin D and Omega-2 Trial), which also signaled that vitamin D reduced cancer deaths, especially in normal-weight subjects. In the VITAL study, which was published in The New England Journal of Medicine, 58 of the 7,800 normal-weight participants in the vitamin D group developed metastatic or fatal cancer compared to 96 in the placebo group.

According to one of the study’s authors, Dr. JoAnn Manson, a professor of medicine at Harvard Medical School, the differences in biological activity of vitamin D in normal-weight versus overweight people could explain the disparity. “It may be that their [overweight people] bodies aren’t using vitamin D as effectively,” she says.

The researchers found no evidence that vitamin D prevented cancer altogether—only that it was linked to a lower risk of developing metastatic cancer or dying from it.

Dr. Manson says that while more research is needed, it is not recommended that everyone take high-dose vitamin D for cancer prevention. Those with a family history of cancer or those previously diagnosed with cancer should avoid vitamin D deficiency and are advised to consume 600 to 800 IU a day. Fatty fish like salmon and tuna, and fortified milk and orange juice are good sources of vitamin D. A supplement is recommended if dietary food sources fall short.