Serum Vitamin D Levels in Relation to Schizophrenia: A Systematic Review and Meta-Analysis of Observational Studies

Introduction: Although several observational studies have investigated the association between vitamin D status and schizophrenia, we are aware of no comprehensive meta-analysis in this regard. Objective: We aimed to conduct a systematic review and a meta-analysis of observational studies to summarize the available data on the association between serum vitamin D levels and schizophrenia. Methods: A systematic research on all published articles until October 2013 was conducted in PubMed, ISI (Web of science), SCOPUS, and Google Scholar. All observational studies that had measured serum vitamin D levels in schizophrenic patients were included in the systematic review. After considering exclusion criteria, wehad 19 studies for the systematic review that were included in three separate meta-analyses: 1) a meta-analysis on mean levels of 25-hydroxyvitamin D [25(OH) D] (n = 13); 2) a meta-analysis on the prevalence of vitamin D deficiency (n = 8); 3) a meta-analysis on odds ratios (n = 8). Results: Findings from a meta-analysis on means revealed that the overall mean difference in serum 25(OH) D levels between schizophrenic patients and control participants was -5.91 ng/mL [95% confidence interval (CI) - 10.68, - 1.14]. Subgroup analyses based on study design, the patient's hospitalization status, study quality, and study location did not explain between-study heterogeneity; however, type of biomarker assessed [25-hydroxyvitamin D-3 vs 25-hydroxyvitamin D (D-2& D-3)] could account for some degree of heterogeneity. Results from the meta-analysis on the prevalence of vitamin D deficiency indicated that the overall prevalence of vitamin D deficiency in schizophrenic patients was 65.3% (95% CI 46.4%-84.2%). Findings from the meta-analysis on odds ratios indicated that vitamin D-deficient persons were 2.16 times (95% CI 1.32, 3.56) more likely to have schizophrenia than those with vitamin D sufficiency. No evidence of heterogeneity was detected. Conclusion: We found a strong association between vitamin D deficiency and schizophrenia. However, randomized clinical trials are required to confirm our findings.