Low level long term fine particulate matter exposure and incidence of dementia in the Puget Sound

Abstract

Background: Growing evidence links ambient air pollution to dementia. The extent to which these effects manifest at low exposure levels is unclear. We utilize a population-based cohort in Seattle to evaluate whether long-term exposure to low-level fine particulate matter (PM2.5) is associated with incidence of all-cause dementia and Alzheimer’s Disease (AD) among the elderly.Methods: Dementia-free individuals aged 65 years and older from Group Health Cooperative (now Kaiser Permanente Washington) were enrolled in the Adult Changes in Thought (ACT) study beginning in 1994; recruitment is ongoing, with 5748 total participants as of January, 2020. We assigned PM2.5 exposure based on national spatial models of annual averages linked to participant addresses. Dementia diagnoses were made using standardized ACT diagnosis protocols at biennial follow-ups. We conducted multivariate Cox proportional hazards regression to evaluate the association between time-varying, 10-year average PM2.5 exposure and time to event for all-cause dementia. Our primary model utilized age as the time axis, included stratification for apolipoprotein E (APOE) genotype status, and adjusted for sex, education, race, neighborhood median household income, and birth cohort. We also ran secondary analyses using additional covariates, alternative exposure average periods, inclusion of nitrogen (NO2) dioxide as a co-pollutant, and restriction to AD.Results: The mean (standard deviation) of 10-year average PM2.5 was 7.9 (1.1) ug/m3, which is below the current national air quality standard. For our primary analysis, we estimated that 1 ug/m3 higher 10-year PM2.5 was associated with a 5% larger expected hazard of all-cause dementia; however, the confidence interval included the null (1.05 (0.94, 1.17)). Results were similar with inclusion of NO2 (1.03 (0.95, 1.13)) and when restricting to AD (1.01 (0.90, 1.14)).Conclusions: Our results are suggestive but inconclusive about the link between low-level PM2.5 air pollution and neurodegeneration, including all-cause dementia and AD.