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

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.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.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]).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.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.