REVIEW OF: Ghaemi S et al, Psychol Med 2024;54(15):1–10

STUDY TYPE: Systematic review and meta-analysis

Vitamin D’s role in mental health has been debated for years, with some studies suggesting benefits and others showing no clear effect. This meta-analysis of 31 RCTs, covering 24,189 adults with depression or anxiety symptoms, helps clarify the picture—finding a dose-dependent antidepressant effect but no benefit for anxiety.

All but 8 of the RCTs lasted longer than 8 weeks (range: 4–256.8 weeks). The studies looked at the effects of vitamin D as monotherapy or in combination with other psychoactive medications, calcium, or omega-3 supplements. Control groups were also heterogenous, with either no intervention, placebo, or treatment as usual. Primary outcomes were improvement in depression and anxiety symptoms as well as remission of depression. Secondary outcomes were quality of life and serious adverse events. 

The meta-analysis found that vitamin D provided dose-dependent relief of depression, but not anxiety, symptoms. Every 1,000 international units (IUs) provided measurable improvement (standardized mean difference [SMD]: -0.32; 95% confidence interval [CI]: -0.43 to -0.22), peaking at 8,000 IU/day (SMD: -2.04; 95% CI: -3.77 to -0.31). Vitamin D did not improve quality of life or depression remission. Researchers did not find a link between vitamin D and serious adverse events, despite a dosage of up to 15,000 IU/day.

Vitamin D therapy was more effective in women, in those with a history of depression, and in those with vitamin D deficiency. Short-term treatment (8–24 weeks) was more effective than long-term treatment, possibly due to adherence or attrition bias from high dropouts. 

CARLAT TAKE
This meta-analysis shows that vitamin D supplementation appears to have a real, dose-dependent antidepressant effect, with peak benefits at 8,000 IU/day. However, it does not seem to improve anxiety, quality of life, or depression remission rates. Given vitamin D’s low cost and good safety profile, it may be a reasonable adjunctive treatment for depression—especially in deficient individuals. Although this study recommended 8,000 IU/day, for patients without a vitamin D deficiency, the NIH recommends no more than 4,000 IU/day due to potential long-term risks like hypercalcemia and kidney issues (https://ods.od.nih.gov/factsheets/VitaminD-Consumer). Until more long-term data are available, higher doses should be approached with caution.