Long-term Air Pollution Exposure Linked With Dementia, Alzheimer Disease

Long-term exposure to fine particulate matter 2.5 (PM_2.5) air pollution may significantly increase risk of dementia, according to study findings published last week in Environmental Health Perspectives.

With the incidence of neurodegenerative disease expected to increase as the population ages, researchers note that there has been an increasing focus on identifying and addressing potentially modifiable risk factors for all-cause dementia, the fifth leading cause of death worldwide.

Notably, air pollution has been linked with the development of neurological conditions such as Parkinson disease and dementia in the past, and it may pose a more dire threat to US populations amid recent cases of wildfires contributing to the spread of PM_2.5 nationwide.

Moreover, last year’s State of the Air Report found an increase in days of ozone and short-term particle pollution than in years past, with many cities experiencing increased levels of year-round particle pollution.

Because the authors of the current study noted that prior research on the link between air pollution and dementia had limitations that affected reliability, they sought to further investigate the association by leveraging data from the Adult Changes in Thought (ACT) population-based prospective cohort study of the Puget Sound region in Seattle, Washington.

Examining the association between time-varying, 10-year average exposure to PM_2.5 and incidence of all-cause dementia (primary analysis) and Alzheimer disease (AD) (secondary analysis), researchers linked spatiotemporal model-based PM_2.5 exposures to participant addresses from 1978 to 2018, with age as the time axis.

Data were stratified by apolipoprotein E (APOE) genotype and adjusted for sex, education, race, neighborhood median household income, and calendar time. Alternative models used calendar time as the time axis.

“We hypothesized that elevated long-term PM_2.5 exposure would be associated with a greater hazard of dementia,” noted researchers. “Given the ubiquity of air pollution, a better understanding of the potential impact of PM_2.5 on AD and related dementias could inform policies to reduce exposures across the population.”

Among ACT study participants examined, 4166 individuals with nonmissing APOE status were identified, of which 1136 cases of incident dementia were found.

In their findings, mean (SD) 10-year average PM_2.5 was shown to be 10.1 (2.9) mcg/m³, and each 1-mcg/m³ increase in the moving 10-year average was associated with a 16% greater risk of all-cause dementia (HR, 1.16; 95% CI, 1.03-1.31).

“How we’ve understood the role of air pollution exposure on health has evolved from first thinking it was pretty much limited to respiratory problems, then that it also has cardiovascular effects, and now there’s evidence of its effects on the brain,” said senior author Lianne Sheppard, PhD, professor of Environmental and Occupational Health Sciences and Biostatistics, University of Washington, in a statement.

Furthermore, each 1-mcg/m³ increase in the moving 10-year average of PM_2.5 was associated with an 11% greater risk of AD diagnosis (HR, 1.11; 95% CI, 0.97-1.27). Results using calendar time as the time axis were similar.

“Having reliable address histories let us obtain more precise air pollution estimates for study participants,” noted Sheppard. “These high-quality exposures combined with ACT’s regular participant follow-up and standardized diagnostic procedures contribute to this study’s potential policy impact.”

Reference

Shaffer RM, Blanco MN, Li G, et al. Fine particulate matter and dementia incidence in the Adult Changes in Thought study. Environ Health Perspect. Published online August 4, 2021. doi:10.1289/EHP9018