Ambient concentrations of NO₂ and hospital admissions for schizophrenia

Schizophrenia is a chronic and severe mental disorder affecting more than 21 million people worldwide. Short-term exposure to nitrogen dioxide (NO₂) has been associated with hospital admissions (HAs) for mental disorders, but no study has evaluated the specific association of NO₂ 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 NO₂ 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.

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 NO₂-schizophrenia relationship.

A total of 11 373 HAs were identified during the study period. An increase in levels of NO₂ was significantly associated with elevated schizophrenia HAs. The estimated relative risk per IQR increase in NO₂ 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 NO₂-schizophrenia relationship suggested possible threshold effects of NO₂ for all ages combined, young patients, men and both seasons.

Short-term exposure to NO₂ may be associated with increased schizophrenia HAs. Findings indicated potential threshold effects of NO₂, which has important implications for health-based risk assessments.