What You Need to Know About Vitamin D and Cancer

Vitamin D helps build healthy bones, but that’s not all it can do. More recent data point to other potential benefits, including staving off dementia and protecting against certain cancers, such as colon and breast cancer.

But how strong is the evidence? In a new study published in JAMA, Joan Lappe, from the Creighton College of Nursing, and her colleagues randomly assigned about 2,300 women who had gone through menopause to take high doses of vitamin D or a placebo. They tracked the women for four years and look out for any cancer diagnoses.

There were no differences in cancer rates between the two groups, but Lappe says that doesn’t mean that vitamin D doesn’t have an effect on cancer. The women in the study tended to already have high levels of vitamin D in their blood—higher than about 80% of U.S. adults, she notes. Most of the women in the study, even in the placebo group, were taking vitamin D or calcium supplements to try to protect their bones and prevent falls and fractures. That means there may not be much difference in cancer outcomes between the group assigned placebo and the women taking the high doses of vitamin D supplements.

Animal studies suggest a number of different ways that vitamin D could be working against cancer. The vitamin stimulates the immune system, which in turn can be activated to target cancer cells; vitamin D may also fight inflammation and other processes that can trigger tumor growth. “I still think the composite of all the evidence together strongly suggests some effect of vitamin D on decreasing cancer risk,” Lappe says.

Not everyone is so encouraged, and many believe that more research on the topic is needed before vitamin D can be considered an anti-cancer weapon. Many cancers take years to develop, and even in the older population in the current study, a longer follow-up period may be necessary to see reliable trends in cancer rates.

What cancer doctors do agree upon, however, is the fact that vitamin D’s potential link to cancer is worth investigating. Studies involving tens of thousands of people who will be assigned high doses of vitamin D or placebo and followed for cancer and heart disease outcomes are ongoing, and their results will continue to add to knowledge about whether vitamin D can be used to combat cancer.