Little is known about the effect of air pollution on Alzheimer's disease (AD)-specific brain structural pathologies. There is also a lack of evidence on whether this effect leads to poorer cognitive function. We investigated whether, and the extent to which, AD-like cortical atrophy mediated the association between air pollution exposures and cognitive function in dementia-free adults. We used cross-sectional data from 640 participants who underwent brain magnetic resonance imaging and the Montreal Cognitive Assessment (MoCA). Mean cortical thickness (as the measure of global cortical atrophy) and machine learning-based AD-like cortical atrophy score were estimated from brain images. Concentrations of particulate matter with diameters ≤ 10 μm (PM10) and ≤ 2.5 μm (PM2.5) and nitrogen dioxide (NO2) were estimated based on each participant's residential address. Following the product method, a mediation effect was tested by conducting a series of three regression analyses (exposure to outcome; exposure to mediator; and exposure and mediator to outcome). A 10 μg/m3 increase in PM10 (β = -1.13; 95 % CI, -1.73 to -0.53) and a 10 ppb increase in NO2 (β = -1.09; 95 % CI, -1.40 to -0.78) were significantly associated with a lower MoCA score. PM10 (β = 0.27; 95 % CI, 0.06 to 0.48) and NO2 (β = 0.35; 95 % CI, 0.25 to 0.45) were significantly associated with an increased AD-like cortical atrophy score. Effects of PM10 and NO2 on MoCA scores were significantly mediated by mean cortical thickness (proportions mediated: 25 %-28 %) and AD-like cortical atrophy scores (13 %-16 %). The findings suggest that air pollution exposures may induce AD-like cortical atrophy, and that this effect may lead to poorer cognitive function in dementia-free adults.
Keywords: Air pollution; Alzheimer’s disease; Cognitive function; Cortical atrophy; Epidemiology; Mediation analysis.
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