Accumulating evidence indicates that alterations in one-carbon metabolism may play an important role in the pathogenesis of schizophrenia. We focused on vitamin B6 (pyridoxal), which works as a coenzyme in one-carbon metabolism. We first conducted a case-control study and demonstrated that serum pyridoxal levels were significantly lower in the schizophrenia group than in the control group. Subsequently, we conducted a meta-analysis of case-control studies and achieved the similar result to the case-control study. Finally, we investigated the causality between serum pyridoxal levels and schizophrenia by a Mendelian randomization analysis. However, we could indicate no significant causality between serum pyridoxal levels and schizophrenia in the Japanese population. Further studies such as a longitudinal study will be needed because there are several studies on the benefits of vitamin B6 in schizophrenia
