According to a combined analysis of previous studies, there is still no clear evidence that vitamin D supplements reduce the risk of cancer. The combination of vitamin D and calcium, however, does appear to reduce the risk of bone fractures in older people. These results were published in the Annals of Internal Medicine.
Vitamin D is important for bone health, and some research suggests that it may also reduce the risk of certain types of cancer. A role for vitamin D in cancer prevention has not yet been firmly established, however, and research on this topic continues. Vitamin D can be produced in the skin in response to ultraviolet B (UVB) radiation from the sun or obtained from dietary sources. Few foods naturally contain large amount of vitamin D, but vitamin D can be obtained from fatty fish such as salmon, fortified foods such as milk, and dietary supplements.
To summarize what is currently known about the effects of vitamin D on bone fractures and cancer, researchers analyzed information from 19 randomized clinical trials and 28 observational studies. In an observational study, scientists do not control what the study participants do. Instead, the scientists observe what happens after the study participants make their own decisions about health behaviors such as supplement use. Results from observational studies are generally not as definitive as results from randomized clinical trials, but they are worth considering as part of the overall body of evidence on a topic.
- Combined calcium and vitamin D reduced the risk of bone fractures in older people, but the optimal dosage remains uncertain. There was some evidence that the fracture benefit may be greater for institutionalized older adults than for community-dwelling older adults.
- The effects of vitamin D on cancer risk are still uncertain.
- Vitamin D supplementation may increase the risk of kidney and urinary tract stones.
These results suggest that vitamin D—in combination with calcium—can play a role in fracture prevention in older adults. There is still no clear evidence that vitamin D reduces the risk of cancer. People who are considering the use of vitamin D or any other dietary supplement are advised to discuss the risks and benefits with their physician.
Reference: Chung M, Lee J, Terasawa T et al. Vitamin D with or without calcium supplementation for prevention of cancer and fractures: an updated meta-analysis for the U.S. Preventive Services Task Force. Annals of Internal Medicine. 2011;155:827-838.