Effects of vitamin D supplementation on depression in adult women: a systematic review of randomized controlled trials

Purpose: This systematic review evaluated the effects of vitamin D supplementation on depressive symptoms in adult women by synthesizing evidence from randomized controlled trials (RCTs).Methods: This review was conducted in accordance with PRISMA 2020 guidelines. PubMed/MEDLINE, Web of Science, PsycINFO, and CINAHL were searched for RCTs published between January 2020 and November 2025. Eligible studies included women aged ≥ 18 years, vitamin D supplementation as the primary intervention, and assessment of depressive symptoms using validated instruments. Two independent reviewers performed study screening, data extraction, and quality assessment using the Cochrane risk of bias 2.0 tool.Results: Four RCTs (n = 18,628 participants) were included. Three trials enrolled women with type 2 diabetes or prediabetes and concomitant vitamin D deficiency, whereas one large trial enrolled adults aged ≥ 50 years without baseline depression. Interventions ranged from 2,000 IU daily to 50,000 IU weekly for 6 months to 5.3 years. Two trials demonstrated significant reductions in depressive symptoms with high-dose supplementation (25,000~50,000 IU weekly) in women with comorbidities and vitamin D deficiency (p < .050). One trial showed overall improvement, but no between-group differences. The large preventive trial (2,000 IU daily, 5.3 years) found no effect on depression incidence (hazard ratio, 0.97; 95% confidence interval, 0.87~1.09).Conclusion: High-dose vitamin D supplementation may be associated with reductions in depressive symptoms among women with vitamin D deficiency and metabolic comorbidities, whereas low-dose supplementation appears to confer limited preventive benefit in the general population.