Associations of PM2.5 intensity and duration with cognitive impairment: A longitudinal analysis of middle-aged and older adults in China

Long-term exposure to air pollution is associated with a higher risk of cognitive impairment; however, the understanding of this association is incomplete. We aimed to explore the relationship between fine particulate matter (PM2.5) exposure and cognitive function using a prospective cohort of ageing adults, including 19,389 respondents in four waves of the China Health and Retirement Longitudinal Study (CHARLS, 2011-2018) linked with the historical PM2.5 concentrations (2000-2018) in China. By extending the measurement of PM2.5 exposure from exposure intensity (averaged PM2.5 concentrations) to exposure duration (the number of months with higher PM2.5 concentrations), we employed two linear models, the fixed-effect and mixed-effect linear models, to estimate the associations between PM2.5 exposure and cognitive impairment, with adjustments for individual and regional covariates. Our findings show that the higher PM2.5 intensity was associated with worse cognitive function, but the associations were only statistically significant in a longer exposure period (more than one year), especially in the 10-year exposure (Coefficient: -0.13; 95% Confidence Interval: -0.22, -0.04). Similar patterns were seen for fully adjusted models of PM2.5 duration: a longer duration in PM2.5 exposure was associated with lower cognitive scores, and the duration with higher cut-off points had stronger effects on cognitive function except for the duration at 75 μg/m3, suggesting a possible coincidence of increasing air pollution and economic development. The stronger exposure to PM2.5 was associated with poorer cognitive function among Chinese adults, while more work is necessary to explore the causal effect of air pollution, independent of individual and contextual background characteristics.