Low levels of serum vitamin D in clozapine-treated schizophrenia patients are associated with high levels of the proinflammatory cytokine IL-6

Low levels of vitamin D are prevalent among patients with schizophrenia and have been linked to the risk and outcome of the disorder. Vitamin D has a regulatory effect on the inflammatory system, which is dysfunctional in schizophrenia. We investigated the association between serum vitamin D levels, inflammatory status, and severity of schizophrenia symptoms. A total of 39 clozapine-treated schizophrenia patients were recruited to the study. Blood samples for biochemical analysis were collected from all participants. Serum levels of vitamin D and cytokines (IL-4, IL-6, IL-10, and TNF-α) were analyzed and the association between biochemical and clinical measures was assessed. Most of the sample (82%) had insufficient levels of vitamin D. There was a significant inverse correlation between serum vitamin D and IL-6 levels (Pearson's r = -0.38, P < 0.05). Vitamin D levels correlated with the severity of positive symptoms (r = 0.39, P < 0.05). These results suggest that within clozapine-treated schizophrenia patients, high levels of vitamin D are associated with lower serum levels of the proinflammatory cytokine IL-6. This relationship may indicate an immunomodulatory effect of vitamin D in treatment-resistant patients with schizophrenia maintained on clozapine.