Long-term exposure to ambient fine particulate matter originating from traffic and residential wood combustion and the prevalence of depression

Introduction Air pollution has been suggested to be associated with depression. However, current evidence is conflicting, and no study has considered different sources of ambient particulate matter with an aerodynamic diameter below 2.5 mu m (PM2.5). We evaluated the associations of long-term exposure to PM2.5 from road traffic and residential wood combustion with the prevalence of depression in the Helsinki region, Finland. Methods We conducted a cross-sectional analysis based on the Helsinki Capital Region Environmental Health Survey 2015-2016 (N=5895). Modelled long-term outdoor concentrations of PM2.5 were evaluated using high-resolution emission and dispersion modelling on an urban scale and linked to the home addresses of study participants. The outcome was self-reported doctor-diagnosed or treated depression. We applied logistic regression and calculated the OR for 1 mu g/m(3) increase in PM2.5, with 95% CI. Models were adjusted for potential confounders, including traffic noise and urban green space. Results Of the participants, 377 reported to have been diagnosed or treated for depression by a doctor. Long-term exposure to PM2.5 from road traffic (OR=1.23, 95% CI 0.86 to 1.73; n=5895) or residential wood combustion (OR=0.78, 95% CI 0.43 to 1.41; n=5895) was not associated with the prevalence of depression. The estimates for PM2.5 from road traffic were elevated, but statistically non-significant, for non-smokers (OR=1.38, 95% CI 0.94 to 2.01; n=4716). Conclusions We found no convincing evidence of an effect of long-term exposure to PM2.5 from road traffic or residential wood combustion on depression.