The effectiveness of vitamin D supplementation in reducing depressive symptoms: A systematic review and meta-analysis of Randomized Controlled Trials (RCTs)

BACKGROUND: Depression is a widespread, global problem, increasingly linked with vitamin D deficiency in the literature. However, a knowledge gap persists regarding the relationship between depressive symptoms and vitamin D intake. OBJECTIVE: To determine the association between vitamin D supplementation and depressive symptoms in adults (aged 18+ years). METHODS: This study consists of a systematic review and meta-analysis of randomized controlled trials (RCTs), published before January 2019. Pooled summary estimates and between-study heterogeneity were examined. RESULTS: Ten RCTs (total participants = 3336; median duration = 12 months) were included. An association was found between high vitamin D supplementation (≥4000 IU) and reduced depressive symptoms, but not in the case of lower levels of vitamin D supplementation (<4000 IU). Neither baseline serum vitamin D before supplementation, nor the depression-scoring scales used affected this association. The overall quality of evidence was graded as ‘moderate’. CONCLUSIONS: Vitamin D supplementation at greater than 4000 IU was observed to have a positive effect on depressive symptoms. Future efforts could focus on obtaining higher-quality evidence with standardized RCT methodologies to confirm this association.