Vitamin D and brain health: A systematic review

Vitamin D, once considered solely important for bone health, is increasingly considered a key neuro-steroid involved in brain development and function. This PRISMA-registered systematic review synthesizes evidence on the association between vitamin D status and neuropsychiatric and neurological disorders and evaluates the effects of vitamin D supplementation on brain-related outcomes. It integrates findings from 90 studies including meta-analyses, clinical trials, and observational studies, about the associations between vitamin D status and the range of neuropsychiatric and neurological disorders. From depression, schizophrenia, and autism spectrum disorders to neurodegenerative disorders such as Alzheimer’s and Parkinson’s, most studies show that low vitamin D is associated with increased risk, increased severity of symptoms, or worse outcomes. Supplementation, particularly for those who are deficient, usually provides improvements resulting in moderate but meaningful improvement in mental health symptoms, neurodevelopmental outcomes, and cognitive function. It is notable and probably most beneficial in individuals with baseline deficiency, and emerging evidence suggests genetic and microbiome factors may impact its benefits. This review emphasizes that vitamin D is a modifiable, low-cost, risk factor for mental and neurological health. This is especially pertinent in vulnerable populations (pregnant individuals; children; aging; psychiatric diagnoses). Vitamin D supplementation cannot be recommended as a primary treatment for neuropsychiatric or neurological disorders, but assessment and correction of deficiency may be considered as part of comprehensive care in selected high-risk populations. The review protocol was registered in PROSPERO (CRD420261282220).