Vitamin D and depression in adults: A systematic review

Depression is one of the most prevalent psychiatric disorders and a leading cause of disability worldwide. Although the pathogenesis of depression remains far from fully understood, current research suggests a potential role for vitamin D due to its involvement in brain functioning. Moreover, vitamin D supplementation has shown promising results in the treatment of patients with depression. Therefore, the present study aimed to systematically review the available research investigating the association between vitamin D levels and the onset of depression. This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the protocol was registered in the PROSPERO database (registration number: CRD42024515918). A search was performed across PubMed/Medline, SCOPUS, and Web of Science databases, yielding a total of 8,052 potentially eligible articles. After the removal of duplicates and ineligible records, and exclusion based on title and abstract screening, 297 original full-text articles were assessed according to the inclusion and exclusion criteria. Ultimately, 66 articles were included in this systematic review. Most of the included studies employed a cross-sectional design (N = 46). Overall, the data analyzed in this review indicate an association between depression and vitamin D serum levels, particularly in studies using cross-sectional designs. Only a few longitudinal studies demonstrated that lower vitamin D levels are associated with an increased risk of developing depressive symptoms or major depressive disorder, highlighting an important research gap. However, it remains to be established through future research whether acute or chronic vitamin D supplementation could have a protective effect against the development of depression.