Exposure to ambient air pollution during childhood and subsequent risk of self-harm: A national cohort study.

Abstract

A growing body of evidence indicates that exposure to air pollution not only impacts on physical health but is also linked with a deterioration in mental health. We conducted the first study to investigate exposure to ambient particulate matter with an aerodynamic diameter of less than 2.5 μm (PM_2.5) and nitrogen dioxide (NO₂) during childhood and subsequent self-harm risk. The study cohort included persons born in Denmark between January 1, 1979 and December 31, 2006 (N = 1,424,670), with information on daily exposures to PM_2.5 and NO₂ at residence from birth to 10th birthday. Follow-up began from 10th birthday until first hospital-presenting self-harm episode, death, or December 31, 2016, whichever came first. Incidence rate ratios estimated by Poisson regression models revealed a dose relationship between increasing PM_2.5 exposure and rising self-harm risk. Exposure to 17-19 μg/m³ of PM_2.5 on average per day from birth to 10th birthday was associated with a 1.45 fold (95% CI 1.37-1.53) subsequently elevated self-harm risk compared with a mean daily exposure of <13 μg/m³, whilst those exposed to 19 μg/m³ or above on average per day had a 1.59 times (1.45-1.75) elevated risk. Higher mean daily exposure to NO₂ during childhood was also linked with increased self-harm risk, but the dose-response relationship observed was less evident than for PM_2.5. Covariate adjustment attenuated the associations, but risk remained independently elevated. Although causality cannot be assumed, these novel findings indicate a potential etiological involvement of ambient air pollution in the development of mental ill health.