Ambient concentrations of NO₂ and hospital admissions for schizophrenia

Objectives Schizophrenia is a chronic and severe mental disorder affecting more than 21 million people worldwide. Short-term exposure to nitrogen dioxide (NO 2 ) has been associated with hospital admissions (HAs) for mental disorders, but no study has evaluated the specific association of NO 2 and schizophrenia. Additionally, the shape of the concentration–response (C–R) curve has not yet been assessed at present. This study aims to investigate the relationship between short-term exposure to NO 2 and HAs for schizophrenia in Hefei, from 2014 to 2016. We also attempt to explore the C–R and the underlying effect modifiers of the association. Methods Daily number of HAs for schizophrenia was derived from the computerised medical record system of Anhui Mental Health Center. We used a time-series Poisson generalised linear regression combined with distributed lag non-linear models to model the NO 2 –schizophrenia relationship. Results A total of 11 373 HAs were identified during the study period. An increase in levels of NO 2 was significantly associated with elevated schizophrenia HAs. The estimated relative risk per IQR increase in NO 2 at lag 01 was 1.10 (95% CI 1.01 to 1.18). Greater association was observed in young patients (relative risk: 1.11, 95% CI 1.02 to 1.19). The modelled C–R curves of the NO 2 –schizophrenia relationship suggested possible threshold effects of NO 2 for all ages combined, young patients, men and both seasons. Conclusions Short-term exposure to NO 2 may be associated with increased schizophrenia HAs. Findings indicated potential threshold effects of NO 2 , which has important implications for health-based risk assessments.