Intake of vitamin D and risk of breast cancer--a meta-analysis.

Vitamin D insufficiency has been shown to be associated with a number of conditions including diabetes, multiple sclerosis and the overall risk of cancer. We aimed at studying the association between vitamin D intake and risk of breast cancer in a meta-analysis. We searched Pubmed, Embase, and Web of Science using the MESH terms "vitamin D" and "breast cancer". A total of 1731 studies were identified, but only 6 studies contained original data on the association between intake of vitamin D and risk of breast cancer. Overall there was no association between amount of vitamin D and risk of breast cancer (RR=0.98, 95% CI: 0.93-1.03, test for heterogeneity p<0.01). However, most studies reported on very low intakes of vitamin D (typically in the range 100-400 IU/day). Restricting the analyses to intakes > or =400 IU/day yielded a more homogenous result with a trend towards less breast cancer with > or =400 IU/day vs. the lowest intake (typically <50-150 IU/day), RR=0.92, 95% CI: 0.87-0.97, p for heterogeneity 0.14. In conclusion there may be a trend towards fewer cases of breast cancer with higher intakes of vitamin D (> or =400 IU/day). However, more research is needed, preferably in the form of randomized-controlled trials.