Effects of PM_2.5 and Its Components on Disease Severity in Patients with Schizophrenia and the Mediating Role of Thyroid Hormones

Studies have indicated the different effects of PM_2.5 components on human health. However, specific components that influence the severity of disease in schizophrenia patients and their underlying mechanisms remain unclear. Therefore, a repeated measures study for schizophrenia was constructed based on Anhui Mental Health Center. We collected information, including demographics and thyroid hormones (TH) levels, on repeat admissions of schizophrenia patients during 2017–2020, assessing their illness severity by positive and negative symptom scales (PANSS). Concentrations from the nearest component monitoring station in the 3 months before admission were assigned as the participant’s exposure level. We assessed the effects of PM_2.5 components individually and in combination on schizophrenia and explored the mediating role of THs. Results indicated that benzo[a]pyrene, sulfate, nitrate, chloride, ammonia, cadmium, chromium, lead, selenium, and thallium exposure were associated with increased PANSS scores, with more significant results observed in males. Mixed exposure to PM_2.5 components was found to be associated with increased PANSS scores and decreased free triiodothyronine (FT3). Mediation analysis suggested that the reduction in FT3 might mediate the association between the PM_2.5 components and PANSS scores. The findings emphasize the impacts of PM_2.5 components on schizophrenia and the potential value of focusing on changes in THs.