Exposure to air pollution during childhood and risk of developing schizophrenia: a national cohort study

Summary: Background: Ambient air pollution affects neurological function, but its association with schizophrenia risk is unclear. We investigated exposure to nitrogen oxides (NOX) as a whole and nitrogen dioxide (NO2) specifically, as well as PM10, and PM2·5, during childhood and subsequent schizophrenia risk. Methods: People born in Denmark from 1980 to 1984 (N=230 844), who were residing in the country on their tenth birthday, and who had two Danish-born parents were followed-up from their tenth birthday until schizophrenia diagnosis or Dec 31, 2016. Mean daily exposure to each pollutant (NO2, NOX, PM10, and PM2·5) at all of an individual's residential addresses from birth to their tenth birthday was modelled. Incidence rate ratios, cumulative incidence, and population attributable risks were calculated using survival analysis techniques. Findings: We analysed data between Aug 1, 2018, and Nov 15, 2019. Of 230 844 individuals included, 2189 cohort members were diagnosed with schizophrenia during follow-up. Higher concentrations of residential NO2 and NOX exposure during childhood were associated with subsequent elevated schizophrenia risk. People exposed to daily mean concentrations of more than 26·5 μg/m3 NO2 had a 1·62 (95% CI 1·41–1·87) times increased risk compared with people exposed to a mean daily concentration of less than 14·5 μg/m3. The absolute risks of developing schizophrenia by the age of 37 years when exposed to daily mean concentrations of more than 26·5 μg/m3 NO2 between birth and 10 years were 1·45% (95% CI 1·30–1·62%) for men and 1·03% (0·90–1·17) for women, whereas when exposed to a mean daily concentration of less than 14·5 μg/m3, the risk was 0·80% (95% CI 0·69–0·92%) for men and 0·67% (0·57–0·79) for women. Associations between exposure to PM2·5 or PM10 and schizophrenia risk were less consistent. Interpretation: If the association between air pollution and schizophrenia is causal, reducing ambient air pollution including NO2 and NOX could have a potentially considerable effect on lowering schizophrenia incidence at the population level. Further investigations are necessary to establish a causal relationship. Funding: Lundbeck Foundation, Stanley Medical Research Institute, European Research Council, NordForsk, Novo Nordisk Foundation, National Health and Medical Research Council, Danish National Research Foundation.