Original ArticlesLow levels of serum vitamin D in clozapine-treated schizophrenia patients are associated with high levels of the proinflammatory cytokine IL-6Krivoy, Amira,,b,,c,,d; Satz, Joshuab,,c; Hornfeld, Shay H.b,,c; Bar, Liorb,,c; Gaughran, Fionad,,e; Shoval, Gala,,b; Hochman, Eldara,,b,,c; Weizman, Abrahama,,b,,c; Taler, Michalb,,cAuthor Information aGeha Mental Health Center, Petach-Tikva bSackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv cLaboratory of Biological Psychiatry, Felsenstein Medical Research Center, Petach-Tikva, Israel dDepartment of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, King’s College London eNational Psychosis Service, South London and Maudsley NHS Foundation Trust, London, UK Received 22 October 2019 Accepted 26 November 2019 Correspondence to Michal Taler, PhD, Laboratory of Biological Psychaitry, Felsenstein Medical Research Center, beilinson campus, Petah Tikva 49100, Israel, Tel: +972 3 9376783; fax: +972 3 9211478; e-mail: firstname.lastname@example.org International Clinical Psychopharmacology: July 2020 - Volume 35 - Issue 4 - p 208-213 doi: 10.1097/YIC.0000000000000303 Buy Metrics Abstract 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. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.