Fine particulate matter may affect racial, ethnic differences in AD

Black women had higher rates of Alzheimer’s disease and environmental exposure to fine particulate matter than white women, according to a prospective, population-based study in Journals of Gerontology: Series A.

“In this study, we asked a big question: ‘Does exposure to environmental neurotoxin, such as the fine particulate matter, or PM_2.5, in the air, make African Americans more likely to develop AD?’” study author Jiu-Chiuan Chen, MD, ScD, of the University of Southern California, told Healio Psychiatry. “We think it is important to study the role of PM_2.5 for two reasons: In the U.S., Black people tend to live in neighborhoods near the facilities that emit particulate matter, and over the last few years, an increasing number of studies have shown that older people are more likely to develop dementia, including AD, if they live in locations with high PM_2.5.”

Between 1995 and 1998, lead author Diana Younan, PhD, MPH, of University of Southern California’s department of preventive medicine, and colleagues enrolled 6,485 postmenopausal women without dementia (6,004 white, 481 Black; aged 65 to 80 years) who participated in the Women’s Health Initiative (WHI) Memory Study, which analyzed hormone therapy in dementia. Follow-up screening determined whether participants had no dementia, mild cognitive impairment or probable dementia; probable dementia was categorized by phenotype.

At follow-up, 158 participants had AD (137 white, 21 Black). Black women had a higher incidence rate (4.88 vs. 2.41 cases per 1,000 person-years) and were more likely to be younger, live in the South, smoke and have lower household incomes and education levels than white women. Black women also drank less alcohol; were less physically active; more frequently had higher BMI, diabetes, hypertension and lived alone; and had more stressful life events with less social support.

Black women had higher exposure levels to PM_2.5 (14.38 ± 2.21 µg/m³) than white women (12.55 ± 2.76 µg/m³). Higher levels of PM_2.5 correlated with older age, residence in the South and Midwest, lower incomes, less alcohol consumption and physical activity, hypercholesterolemia, hypertension and more social activity.

The connection between PM_2.5 and AD risk was twice as high among Black women (HR_PM2.5 = 2.10-2.60) compared with white women (HR_PM2.5 = 1.07-1.15). With adjustment for sociodemographic factors, comorbidities, lifetime stress and lifestyle, Black women still had a stronger link between the two (HR_PM2.5 = 1.85; 95% CI, 1.14 to 3.01).

“These novel results provide the first direct evidence linking environmental pollutants with racial/ethnic disparities in AD risk,” the researchers wrote.

While the study was strengthened by its large sample size, geographic generalizability, prospective follow-up and bias adjustment, it was limited by potential “perceived discrimination” toward Black people that may have affected cognitive performance, non-examination of environmental factors aside from PM, inability to assess the entirety of lifetime experience, relatively small group of Black participants and specificity to older women.

Moving forward, Younan and colleagues suggested placing more emphasis on PM_2.5 in research and environmental regulation.

“Future studies should investigate whether the neurotoxic effects of PM_2.5 may interact with these contextual factors resulting from structural racism to impact brain aging,” they wrote. “Additionally, the collective evidence demonstrating the increased susceptibility to the health effects of PM_2.5 amongst Black populations highlights the need for stronger enforcement of the Clean Air Act’s mandate to provide safe margins of air quality for susceptible populations.”