Q&A: Vitamin D

Q: Should I increase my vitamin D intake?

A: There has been a lot of discussion recently about the role of vitamin D and its impact on health. We know that vitamin D improves bone and muscle health, but does it also have a role in preventing cancer or perhaps improving the outlook for people diagnosed with new cancers?

A recent study presented at the annual meeting of the American Society of Clinical Oncology this past summer suggests that women with newly diagnosed breast cancer may fare better if they have adequate levels of vitamin D compared with deficient levels at the time of diagnosis. The research, performed at several hospitals in Toronto, Canada, took blood samples from more than 500 women diagnosed with primary breast cancer from 1989 through 1995. The researchers measured the levels of vitamin D in the blood samples and then followed the women through 2006.

They found that about three out of four women had vitamin D levels that were either clearly deficient or below recommended amounts. When examining the percentage of patients who developed metastatic breast cancer within five to 10 years, women who were deficient in vitamin D had a higher chance of distant recurrence compared with women with adequate levels. They found a similar relationship when looking at overall survival, with vitamin D-deficient women having a higher chance of dying than women with adequate levels.

This is not the first time low vitamin D levels were associated with cancer outlook. Several studies suggest lower vitamin D levels are associated with an increased frequency of several cancers, including colorectal cancer. However, other studies show vitamin D levels are not associated with an overall decrease in cancer deaths from all causes.

What should you do? The American Cancer Society does not recommend that you “seek the sun” to increase your vitamin D or overload on supplements. You can get vitamin D from a combination of moderate sunlight, food, and supplements (preferably vitamin D3) that are readily available, inexpensive, and considered safe in typical doses.

However, it’s unclear whether vitamin D level directly affects cancer risk or whether it might simply be an indicator associated with a different causative factor. The study’s authors stopped short of recommending vitamin D specifically for preventing cancer recurrence.

Current allowances are mostly intended for maintaining bone health and other physiologic functions. Talk to your doctor about the recommended daily allowance, which should be between 200 and 600 IU depending on age and gender.

Len Lichtenfeld, MD, is deputy medical officer for the American Cancer Society.