Lower vitamin D consistently linked with higher depression in adults

Researchers report in a study, published in Biomolecules and Biomedicine, that lower blood levels of vitamin D are consistently linked with higher rates of depression in adults—especially when 25-hydroxy-vitamin D [25(OH)D] falls at or below 30 nmol/L.

The authors emphasize that this does not prove cause: in prospective (forward-looking) cohorts, results were mixed, underscoring the need for tighter causal tests.

The team synthesized 66 observational studies drawn from 31 countries, after screening 8,052 records across PubMed/MEDLINE, Scopus, and Web of Science through April 30, 2023. Because vitamin D assays and depression measures varied widely, they conducted a narrative synthesis rather than a meta-analysis and rated study quality using the MMAT and MINORS tools.

Depression affects about 5% of adults worldwide and is projected to become the leading cause of disease burden by 2030. Conventional antidepressants help many patients but, on average, deliver only “small to moderate” effects, leaving room to explore safe, modifiable biological factors such as vitamin D.

Biologically, the case for vitamin D is plausible. Receptors are abundant in mood-relevant brain regions, including the hypothalamus and pons. The active metabolite, 1,25-dihydroxy-vitamin D, supports neurotrophic signaling, tempers neuro-inflammation, limits oxidative stress, and helps balance intracellular calcium—pathways long implicated in depressive pathophysiology.

Across 46 cross-sectional studies, lower 25(OH)D reliably tracked with higher depressive symptom scores or clinical diagnoses. Thresholds mattered: the ≤ 30 nmol/L range most consistently coincided with depression across designs.

In strictly prospective cohorts (n=10), however, findings diverged: some reported a higher risk of incident depression at lower vitamin D levels, while others—such as large biobank analyses—found no association over follow-up.

Methodological heterogeneity was a recurring challenge. Eight different depression instruments (including CES-D, PHQ-9, GDS, BDI, IDS-SR30, HAM-D, DASS-21, and structured DSM/ICD interviews) and multiple vitamin D assays complicated pooling.

Many studies did not uniformly control for sun exposure, BMI, or medical comorbidities, leaving room for residual confounding. Some cohorts reported associations only in women, suggesting possible sex-specific effects that require dedicated study.

“Our takeaway is cautious but practical: check vitamin D in adults with depression and correct clear deficiency for overall health—while we run rigorous studies to test whether restoring vitamin D can actually prevent depression,” said Vlad Dionisie, Ph.D., Assistant Professor at Carol Davila University of Medicine and Pharmacy.

The protocol followed PRISMA-2020 guidelines and was registered in PROSPERO (CRD42024515918).

The authors call for cohorts with repeated vitamin D measures, objective sunlight exposure metrics and genotype data (e.g., VDR, GC) to probe causal pathways, as well as randomized prevention trials in vitamin-D-deficient, depression-free adults.

More information:
Vlad Dionisie et al, Vitamin D and depression in adults: A systematic review. Biomolecules and Biomedicine (2025). doi.org/10.17305/bb.2025.12331