Long-term exposures to PM2.5, BC and NO2 and mental health among French adults: The CONSTANCES Cohort

Abstract Background Ambient air pollution has been suggested to be associated with mental health, however the isolated effect of black carbon (BC) has been rarely studied, even though BC was pointed as of special interest by world health organization (WHO). Objectives To examine the associations between annual exposure to particulate matter with a diameter < 2.5 µm (PM2.5), BC and nitrogen dioxide (NO2) and psychological distress in the French CONSTANCES cohort, and assess the effect of BC independently of PM2.5. Methods This cross-sectional study included 117,697 adults. Psychological distress was assessed in 2019 using the General Health Questionnaire-12 (GHQ-12, from 0 to 12). Annual concentrations of PM2.5, BC, and NO2 estimated from land-use regression models, were assigned to each participant's residential address. Negative binomial models adjusted for age, sex, health center of inclusion, education, smoking, season and the French deprivation index were used. The residuals method used to assess BC's independent effect. Results are presented using incident rate ratio (IRR) per interquartile range (IQR) increase in exposure of each pollutant. Stratified analyses by age, sex, education and season were also conducted. Results Mean concentrations were 16.9 µg/m3 for PM2.5 (IQR = 2.59), 1.78 10-5/m for BC (IQR = 0.45) and 25.7 µg/m3 and NO2 (IQR = 11.49). Exposure to all three pollutants was significantly associated with higher GHQ-12 scores (IRR (95%CI) = 1.053 (1.017-1.090) for PM2.5, 1.068 (1.047-1.090) for BC and 1.072 (1.048-1.097) for NO2). BC residuals also showed a significant association (1.20 (1.14 - 1.27)). Stronger associations were found for men, elderly, lower-education and respondents during warm season. Conclusions This study is among the few showing that exposure to ambient air pollution is associated with increased psychological distress in a large adult sample. The findings highlight the need to reduce air pollution to promote population mental health. Key messages • Our study showed that long-term exposure to NO2, PM2.5, and BC, was associated to higher psychological distress, highlighting air quality improvement as a strategy for mental health promotion. • Among the three pollutants associated with higher psychological distress, BC is of particular interest, as it has been not explored before and may open new paths to focused public health actions.