Racial and ethnic differences in the impact of air pollution on the risk of Alzheimer’s disease and related dementias in the Multiethnic Cohort Study

Background and Objectives Meta-analysis results, based largely among Whites, suggested that fine particulate matter (PM2.5) exposure increases the risk of clinical dementia. This study investigated the association of air pollution and incidence of Alzheimer’s disease and related dementias (ADRD) by race and ethnicity. Methods We investigated incidence of AD (n = 4,010) and other dementia (n = 4,971) among 44,954 California Multiethnic Cohort (MEC) participants (28% African American, 14% Japanese American, 44% Latino, 14% White adults) who were enrolled in the fee-for-service component of Medicare (2001–2016). We used Cox proportional hazards regression to examine associations between exposure to PM, airport-related ultrafine particles (aUFP) and gaseous pollutants and incidence of AD, other dementia, and ADRD in a minimally- and fully-adjusted model, considering12 established ADRD risk factors. We conducted stratified analyses to examine associations by sex, and race/ethnicity. Results ADRD incidence was associated with PM 2.5 (per 2 µg/m3), airport-related UFP (aUFP, per 4400 particles/cm3) and nitrogen dioxide (NO 2, per 10 µg/m3) with hazard ratios (HRs, 95%CI), respectively, of 1.04 (1.02–1.06), 1.03 (1.01–1.05) and 1.09 (1.06–1.12). The AD-associations with PM 2.5 and NO 2, were stronger than the corresponding associations with other dementia (Pheterogeneity ≤ 0.003). Similar patterns of results were observed by sex and across race and ethnicity. Statistically significant findings for ADRD with PM 2.5, aUFP and NO 2 were observed among African American (respective HRs 1.03, 1.04, 1.09), and Latino and White participants for NO2 (HR 1.10, 1.08). Results in all and African American participants remained statistically significant in fully-adjusted models. Although the effect of PM 2.5 was diluted in a co-pollutant with NO2, but both PM 2.5 and aUFP were significantly associated with ADRD incidence in a co-pollutant model, and NO 2 and aUFP (but not PM2.5) significantly increased ADRD incidence in a multipollutant model. We did not observe consistent modifying effect of any of the 12 established ADRD risk factors. Conclusions In this multiethnic population, incidence of ADRD increased with exposures to PM2.5, aUFP, and NO2 in all subjects and this pattern was most prominent among African American adults. These results emphasize that ADRD prevention should include not only individual-level factors but also population-wide policies and regulation to curb air pollution.