Academic Editor: Gernot Riedel
Objective: Vitamin D (VitD) has been shown to influence several cellular processes in the brain. The extent to which VitD plays a role in the pathomechanism of neuronal loss and dysfunction in basal ganglia diseases (BGDs) is still debated. There is yet to be a comprehensive study that provides an overview of all of the most relevant BGDs. Methods: PubMed, and Google Scholar were systematically searched for observational studies that investigated the association between serum VitD levels and BGDs up to March 2022. Results: We extracted 60 studies, but with a great variety of design and quality. VitD deficiency appears to be common in most BGDs, but only in Parkinson’s disease (PD) has a causal association been fully examined. There is some evidence that low VitD serum levels influence symptom severity, most notably in restless legs syndrome (RLS), PD, and tic disorders. The effects of vitamin D supplementation were studied in three BGDs, with results mostly favorable for RLS, ambiguous for tics, and mostly unfavorable for PD. Conclusions: There are still various elements of BGDs with insufficient, ambiguous, or altogether absent evidence, and further high-quality research is required. However, there appears to be sufficient scientific justification already to recommend that practitioners treating BGDs check serum VitD levels and supplement as appropriate.