Inflammation in Schizophrenia: Cytokine Levels and Their Relationships to Demographic and Clinical Variables

OBJECTIVE: Inflammation may play a role in the accelerated physical aging reported in schizophrenia though biomarker findings and associations with demographic and clinical factors are inconsistent. DESIGN: Cross-sectional, case-control design SETTING: Community-dwelling participants tested in an academic laboratory. PARTICIPANTS: 95 outpatients with schizophrenia (mean age ± SD: 48.1 ± 10.2 yrs) and 95 demographically-comparable healthy comparison subjects (HCs) (mean age ± SD: 48.1 ± 12.1 yrs) MEASUREMENTS: Sociodemographic and clinical data were collected, and plasma levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interferon-γ (IFN-γ) were assayed. We compared cytokine levels, examined demographic and clinical associations. and adjusted for relevant variables with linear models. RESULTS: Individuals with schizophrenia had higher levels of TNF-α and IL-6, but not IFN-γ, than HCs. Age was not related to cytokine levels, and age relationships did not differ between diagnostic groups. Women had higher levels of IL-6. TNF-α and IL-6 levels were significantly correlated with depressive symptoms, and adjustment for depression reduced the group effect for both. Within the HCs, TNF-α levels were associated with physical comorbidity and body mass index (BMI). IL-6 levels were significantly correlated with BMI, and within schizophrenia patients, with worse mental and physical well-being. Accounting for physical morbidity and mental well-being reduced group differences in TNF-α and IL-6 levels, respectively. Worse positive symptoms were associated with higher IL-6 levels. CONCLUSIONS: Higher TNF-α and IL-6 levels in schizophrenia patients were associated with depression, physical comorbidity, and mental well-being. Further longitudinal studies are warranted to assess inflammation as a potential treatment target for a subgroup of schizophrenia