The role of vitamin D in preventing cancer is a growing area of interest. A number of studies have shown an inverse relationship between cancer risk and sunlight exposure.
A randomised clinical trial was conducted to measure the effect of vitamin D3 and calcium supplements on the risk of all-type cancer in 2,303 healthy, postmenopausal women whose blood levels of vitamin D were already above the current recommended level.
In total, 1,156 women were allocated to the treatment group, while 1,147 were allocated to placebo.
After four years of follow-up, the researchers noted that a new diagnosis of cancer had been made in 45 women in the treatment group and 64 women who were given placebo.
Reporting in the Journal of the American Medical Association
(online, 28 March 2017), the researchers conclude that although supplementation decreased the incidence of cancer by 30%, the effect was not statistically significant. They say further research is needed to confirm the role of vitamin D in cancer prevention.
 Lappe J, Watson P, Travers-Gustafson D et al. Effect of vitamin D and calcium supplementation on cancer incidence in older women: a randomized clinical trial. JAMA 2017;317(12):1234-1243. doi: 10.1001/jama.2017.2115