Exposure to Ambient Air Pollutants Linked to Risk for Alzheimer Disease

Chronic exposure to fine particulate matter (PM_2.5) is associated with increased risk of developing Alzheimer disease (AD), according to study results published in Journal of Alzheimer’s Disease.

Ambient air contaminants, even at low levels, may increase the risk for AD, related dementias, and cognitive impairment, though findings remain inconsistent. The role of absolute and relative concentration–response measures in this relationship has yet to be fully explored.

Researchers analyzed Medicare claims data from 1991 to 2020 to assess absolute and relative concentration–response associations between PM_2.5 exposure and AD risk, while identifying vulnerable subpopulations. Ambient PM_2.5 levels were linked to health records by ZIP code, and demographic information, follow-up duration, and AD onset were recorded. Follow-up period ranged from age of enrollment in traditional Medicare to age of AD diagnosis, death, last date of insurance coverage, or age 110 years.

A total of 3,455,411 individuals with PM_2.5 exposure were included in the analysis. The researchers found that age modified the PM_2.5 concentration-response function relationship with AD risk among individuals older than 65 years. However, there was significant variation in this association across sex and race/ethnicity subgroups.

Women had higher absolute AD incidence, but men had steeper relative increases in AD incidence. Black and Native American individuals had the highest absolute rates, while Asian individuals had the lowest.

Despite residing in areas with the lowest PM_2.5 concentrations, based on relative concentration-response patterns, Native American individuals showed the sharpest increase in AD risk with rising exposure. Black and Asian groups had the lowest relative ratios. In contrast, among Hispanic individuals, AD risk decreased at PM_2.5 exposures of greater than 8 μg/m³, which can likely be attributed to self-reported data and substantial geographic heterogeneity. In most subpopulations, AD incidence rates plateaued at levels of PM_2.5 of greater than 15 μg/m³.

Study limitations include risk of selection bias from excluding Medicare Advantage enrollees, unmeasured factors such as socioeconomic status, and potential misclassification from using ZIP codes for geographic data.

The researchers concluded, “By demonstrating how factors such as age, sex, race/ethnicity, and geographic location shape exposure-risk relationships, we provide a foundation for more-nuanced modeling, improved public-health planning, and targeted interventions.”