The effect of vitamin D supplementation on primary depression: A meta-analysis.

Background: Previous meta-analyses reported inconsistent results on the effect of vitamin D on depression because of different baseline concentrations of 25-hydroxyvitamin D [25(OH)D], highlighting the need for a more accurate subgroup analysis of previously published findings. The goal of the present study was to evaluate the effect of vitamin D supplementation on depression in adults.

Methods: A systematic search in numerous databases including PubMed, Embase, and Web of Science was performed. Randomized-controlled trials comparing the effect of vitamin D on depression in adults were selected.

Results: Eighteen studies met the inclusion criteria in the retrieved citations. The meta-analysis showed that vitamin D supplementation had a significant effect on overall reduction in depression symptom scores (SMD = -0.15, 95 % CI [-0.26, -0.04]). Sub-group analysis showed that vitamin D supplementation significantly reduced depressive symptom scores in patients with serum 25(OH)D levels higher than 50 nmol/L (SMD = -0.38, 95 % CI [-0.68, -0.08]).

Conclusions: Vitamin D supplementation has a benefit on improving depressive symptoms in adults with primary depression and 25(OH)D levels higher than 50 nmol/L but has no effect on improving depressive symptoms in adults with primary depression and 25(OH)D levels lower than 50 nmol/L. Relatively high levels of 25(OH)D maybe required for alleviating depression.

Limitations: The randomized studies included in this study were designed and completed at different times and countries, the variability in duration and dose of vitamin D supplementation may have introduced significant heterogeneity and have militated against observation of the effects of vitamin D supplementation on depression.