Associations of long-term exposure to air pollution and road traffic noise with cognitive function—An analysis of effect measure modification

Background Adverse effects of traffic-related air pollution (AP) and noise on cognitive functions have been proposed, but little is known about their interactions and the combined effect of co-exposure. Methods Cognitive assessment was completed by 4086 participants of the population-based Heinz Nixdorf Recall cohort study using five neuropsychological subtests and an additively calculated global cognitive score (GCS). We assessed long-term residential concentrations for size-fractioned particulate matter (PM) and nitrogen oxides with land use regression. Road traffic noise (weighted 24-h (L_DEN) and night-time (L_NIGHT) means) was assessed according to the EU directive 2002/49/EC. Linear regression models adjusted for individual-level characteristics were calculated to estimate effect modification of associations between AP and noise with cognitive function. We used multiplicative interaction terms and categories of single or double high exposure, dichotomizing the potential effect modifier at the median (AP) or at an a priori defined threshold (road traffic noise). Results In fully adjusted models, high noise exposure increased the association of AP with cognitive function. For example, for an interquartile range increase of PM_2.5 (IQR 1.43), association s with GCS were: estimate (β) = − 0.16 [95% confidence interval: − 0.33; 0.01] and β = − 0.48 [− 0.72; − 0.23] for low and high L_DEN, respectively. The association of noise with GCS was restricted to highly AP-exposed participants. We observed stronger negative associations in those participants with double exposure compared to the addition of effect estimates of each single exposure. Conclusions Our study suggests that AP and road traffic noise might act synergistically on cognitive function in adults.