Meta-analysis of randomized controlled trials on vitamin D supplement and cancer incidence and mortality

We aimed to meta-analyze the results of published randomized controlled trials to test the hypothesis that low vitamin D supplement is associated with an increased risk of cancer incidence and mortality.

Randomized controlled trials that explored the association between vitamin D supplement and cancer incidence or mortality as primary outcomes were identified through searching the PubMed and EMBASE. Literature search and data extraction were performed independently and in duplicate.

Ten randomized controlled trials pooled in 81362 participants. The incidence rate of cancer was 9.16% (3716 cases) and 9.29% (3799 cases) in vitamin D intervention group and placebo group, respectively, resulting in a nonsignificant relative risk (RR) (95% confidence interval (95% CI)) of 0.99 (0.94-1.03) (P=0.532). The mortality rate of cancer was 2.11% (821 cases) and 2.43% (942 cases) in vitamin D intervention group and placebo group, respectively, resulting in a significant reduction in risk (RR = 0.87, 95% CI: 0.79-0.95, P=0.003). There was no observable heterogeneity or publication bias. Subgroup analyses revealed that history of cancer, extra use of vitamin D and calcium supplement were potential sources of heterogeneity.

Our findings support a beneficial effect of vitamin D supplement on lowering cancer mortality, especially in subpopulations with no history of cancer, extra use of vitamin D, or calcium supplement.