Mediation Analysis of the Role of Air Pollution on the Relationship between Road Network Density and Cognitive Function: Results from a Cross-Sectional Study among Adults Age 60 and Older in Liaoning, China

Abstract Background: Research on the relationship between road network density and cognitive function is lacking, and air pollution is related to both issues.Objective: We examined the mediating role of air pollution in relationship to road network density and cognitive function of older adults in Liaoning, China.Methods: This analysis included 745 adults age 60 and older. We obtained road network density for total roads, main roads, secondary roads, and other roads by OpenStreetMap and QGIS. We used air quality index (AQI) for the whole year, heating period, and nonheating period to assess individual air pollution exposure levels in different periods. We measured cognitive function using the Mini-Mental State Examination (MMSE). We used mediation analysis to evaluate the role of air pollution in the relationship between road network density and cognitive function.Results: The relationship between total road network density and global cognitive function was positive (β>0, p<0.01), and air pollution had a suppressing effect. The main road network density and cognitive function were negatively correlated, and the mediating effect of air pollution for all three periods accounted for 81.69%–90.09% of the total effects. The other road network density and cognitive function were positively correlated, and the suppressing effect of air pollution for all three periods accounted for 10.06%–18.50% of the total effects. The secondary road network density and cognitive function were positively correlated, and the suppressing effect of air pollution in the whole year and heating period accounted for 21.06% and 26.10% of the total effects, respectively. During nonheating period, the suppressing effect of air pollution was not statistically significant [β = −0.018; standard error (SE) = 0.014; 95% confidence interval (CI): −0.046, 0.007].Conclusion: Because the different categories of road network density have different relationships with cognitive function, air pollution had different effects on these relationships.