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

Background
Ambient air pollution impacts on neurological functions, but its association with schizophrenia risk is unclear. We investigated exposure to nitrogen dioxide (NO2), nitrogen oxides (NOx), particulate matter with aerodynamic diameters of less than 10 µm (PM10) and 2.5µm (PM2.5), during childhood and subsequent schizophrenia risks.

Methods
Persons born in Denmark 1980-1984 (N=230,844) were followed up from 10th birthday until schizophrenia diagnosis or 31st December 2016. Mean daily exposure to each pollutant at residential addresses from birth to 10th birthday was modelled. Incidence rate ratios, cumulative incidence, and population attributable risks were calculated using survival analysis techniques.

Findings
A total of 2189 cohort members were diagnosed with schizophrenia during follow-up. Higher levels of residential NO2 and NOx exposure during childhood were associated with subsequent elevated schizophrenia risk. For example, persons exposed to daily means above 26·5 μg/m3 NO2 had a 1·62 (95% CI 1·41-1·87) fold increased risk compared with persons exposed to mean daily level of less than 14·5 μg/m3. The corresponding absolute risks of developing schizophrenia by age 37 for males were 1·45% (95% CI 1·30-1·62%) and 0·80% (95% CI 0·69-0·92%), respectively. Associations between exposure to PM2.5 or PM10 and schizophrenia risk were less consistent.

Interpretation
If the association is causal, reducing ambient air pollution including NO2 and NOx could have a potentially considerable impact on lowering schizophrenia incidence at whole population level.