Short-term exposure to air pollution and depressive symptoms: Findings from the French CONSTANCES cohort

Major depressive disorders pose a substantial public health burden, with emerging evidence linking these disorders to air pollution. To investigate the association between short-term exposure to air pollution and depressive symptoms, focusing on particulate matter with a diameter ≤ 2.5 μm (PM 2.5 ) and nitrogen dioxide (NO 2 ). Data from the enrollment phase of the French CONSTANCES cohort (2012–2016) were analyzed cross sectionally. For each participant, we assigned the median concentrations of PM 2.5 and NO 2 , estimated by the CHIMERE model, over the seven days preceding completion of the Centre of Epidemiologic Studies Depression (CES-D) scale to their residential addresses . We assessed depressive symptoms using the CES-D and defined clinically significant depressive symptoms (binary variable) with the validated threshold of 19. We used negative binomial regression models (yielding Incidence Rate Ratio (IRR) and 95% confidence interval (CI)) and logistic regression models (yielding Odds Ratio (OR) and 95% CI), for an interquartile range (IQR) increase in exposures, adjusted for two sets of confounders. 105,976 participants (mean age, 47.3 ± 13.7 years; 53% women) were included. The 7-day median PM 2.5 and NO 2 exposures were 8.4 µg/m 3 (IQR: 5.9–12.2) and 2.2 µg/m 3 (IQR: 1.3–3.5), respectively. Short-term exposures to PM 2.5 and NO 2 were positively associated with a higher CES-D score (IRR = 1.009 (95% CI: 1.003–1.014) and IRR = 1.009 (95% CI: 1.004–1.014), respectively) and with higher rates of clinically-significant depressive symptoms (OR = 1.027 (1.008–1.046) and OR = 1.031 (1.012–1.051), respectively). These results were consistent across sensitivity analyses. There was an interaction between BMI and exposure to NO 2 , with a significant effect only among subjects with obesity. Our results suggest that air pollution may affect mental health, even at a subclinical level, warranting further research especially during pollution peaks. However, this study could not establish causality.