Vitamin D supplementation for depressive symptoms: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE The aim of this study was to review the effects of vitamin D supplementation on depressive symptoms in randomized controlled trials. Although low vitamin D levels have been observationally associated with depressive symptoms, the effect of vitamin D supplementation as an antidepressant remains uncertain. METHODS MEDLINE, CINAHL, AMED, PsycINFO, Scopus, The Cochrane Library, and references of included reports (through May 2013) were searched. Two independent reviewers identified and extracted data from randomized trials that compared the effect of vitamin D supplementation on depressive symptoms to a control condition. Two additional reviewers assessed study quality using The Cochrane Risk of Bias Tool. Seven trials (3191 participants) were included. RESULTS Vitamin D supplementation had no overall effect on depressive symptoms (standardized mean difference [SMD], 0.14; 95% confidence interval [CI], -0.33 to 0.05, p = .16), although considerable heterogeneity was observed. Subgroup analysis showed that vitamin D supplementation for participants with clinically significant depressive symptoms or depressive disorder had a moderate, statistically significant effect (2 studies: SMD, -0.60; 95% CI, -1.19 to -0.01; p = .046), but a small, nonsignificant effect for those without clinically significant depression (5 studies: SMD, -0.04; 95% CI, -0.20 to 0.12; p = .61). Most trials had unclear or high risk of bias. Studies varied in the amount, frequency, duration, and mode of delivery of vitamin D supplementation. CONCLUSIONS Vitamin D supplementation may be effective for reducing depressive symptoms in patients with clinically significant depression; however, further high-quality research is needed.