Vitamin D-containing supplementation and depressive symptom severity in adults: A Bayesian systematic review and evidence-structure assessment.

BACKGROUND & AIMS: Vitamin D supplementation has been proposed as a nutrition-related adjunctive strategy for depressive symptoms, but randomized evidence remains heterogeneous, and the feasibility of comparing multicomponent vitamin D-containing regimens is unclear. We evaluated the effects of vitamin D-containing supplementation on depressive symptom severity in adults and assessed whether the evidence structure supported network or component-level inference. METHODS: We searched PubMed, Embase, CENTRAL, ClinicalTrials.gov, and WHO ICTRP from inception to 15 April 2026. Randomized studies of vitamin D-containing nutritional interventions in adults with depressive disorders or clinically relevant depressive symptoms were included. The primary analysis was a Bayesian random-effects pairwise meta-analysis of endpoint depressive symptom scores in the oral vitamin D evidence layer. Frequentist endpoint and change-score analyses were used as robustness checks. Treatment-network connectivity and component estimability were assessed before any network or component network meta-analysis was attempted. RESULTS: Thirteen randomized studies published between 2013 and 2024 were retained. Seven studies with eight endpoint contrasts contributed to the Bayesian oral endpoint synthesis. Vitamin D-containing supplementation favored lower depressive symptom severity compared with comparators, with a posterior median SMD of -0.88 (95% credible interval, -1.38 to -0.35). Directional probabilities favored benefit, but between-study heterogeneity was substantial and posterior predictive intervals crossed the null. The treatment network was fragmented, and co-nutrient variation was sparse; therefore, formal network meta-analysis, treatment ranking, and component-level nutrient-synergy estimation were not methodologically defensible. CONCLUSION: Vitamin D-containing supplementation shows a favorable but heterogeneous signal for depressive symptom severity in adults. Current randomized evidence supports cautious pairwise synthesis but not clinical treatment ranking or claims of incremental benefit from specific co-nutrients. Better replicated, vitamin D status-stratified, and component-informative trials are needed.