Traffic-related air pollution and dementia incidence in the Adult Changes in Thought Study

Abstract

Background: While epidemiologic evidence links higher levels of exposure to fine particulate matter (PM_2.5) to decreased cognitive function, fewer studies have investigated links with traffic-related air pollution (TRAP), and none have examined ultrafine particles (UFP, ≤100 nm) and late-life dementia incidence.

Objective: To evaluate associations between TRAP exposures (UFP, black carbon [BC], and nitrogen dioxide [NO₂]) and late-life dementia incidence.

Methods: We ascertained dementia incidence in the Seattle-based Adult Changes in Thought (ACT) prospective cohort study (beginning in 1994) and assessed ten-year average TRAP exposures for each participant based on prediction models derived from an extensive mobile monitoring campaign. We applied Cox proportional hazards models to investigate TRAP exposure and dementia incidence using age as the time axis and further adjusting for sex, self-reported race, calendar year, education, socioeconomic status, PM_2.5, and APOE genotype. We ran sensitivity analyses where we did not adjust for PM_2.5 and other sensitivity and secondary analyses where we adjusted for multiple pollutants, applied alternative exposure models (including total and size-specific UFP), modified the adjustment covariates, used calendar year as the time axis, assessed different exposure periods, dementia subtypes, and others.

Results: We identified 1,041 incident all-cause dementia cases in 4,283 participants over 37,102 person-years of follow-up. We did not find evidence of a greater hazard of late-life dementia incidence with elevated levels of long-term TRAP exposures. The estimated hazard ratio of all-cause dementia was 0.98 (95 % CI: 0.92-1.05) for every 2000 pt/cm³ increment in UFP, 0.95 (0.89-1.01) for every 100 ng/m³ increment in BC, and 0.96 (0.91-1.02) for every 2 ppb increment in NO₂. These findings were consistent across sensitivity and secondary analyses.

Discussion: We did not find evidence of a greater hazard of late-life dementia risk with elevated long-term TRAP exposures in this population-based prospective cohort study.

Keywords: Alzheimer’s Disease (AD) and related dementias (ADRD); Black carbon (BC); Cohort; Nitrogen dioxide (NO2) traffic-related air pollution; Ultrafine particles (UFP).

Fig. 1.

Estimated hazard ratios for the estimated hazard ratio of all-cause dementia incidence associated with an increment in ten-year average TRAP exposure. Single pollutant Cox proportional hazards models use age as the time axis, are stratified by APOE genotype, and further adjust for sex, race, calendar year, education, and NDI. Two pollutant (primary) models further adjust single pollutant models for PM_2.5. The four-pollutant model includes PNC, BC, NO₂, and PM_2.5 in a single model.

Fig. 2.

UFP sensitivity (total PNC) and secondary (size-specific PNC and size) analyses for the estimated hazard ratio of all-cause dementia incidence associated with an increment in ten-year average UFP (1000pt/cm³) exposure. Cox proportional hazard models are similar to the primary UFP two pollutant models but use exposures from different UFP models.