Summary: A new 17-year study has identified a direct association between long-term exposure to fine particulate air pollution (PM2.5) and accelerated decline in a specific area of cognition: semantic memory. The research followed a cohort of Black adults enrolled in the Study of Healthy Aging in African Americans (STAR).
The results show that prolonged exposure to microscopic airborne particles—PM2.5—appears to target semantic memory, the cognitive system that stores facts, word meanings and general knowledge. The observed decline in semantic memory among those with higher long-term exposure was greater than what researchers would typically expect from ten years of biological aging.
Key Facts
- Semantic memory vulnerability: Long-term PM2.5 exposure was associated with selective reductions in semantic memory, which supports communication, comprehension and day-to-day independence.
- Study duration and sample: Researchers tracked 740 adults aged 53 to 94 and mapped daily PM2.5 at each participant’s residential address across 5-, 10- and 17-year exposure windows.
- Magnitude of effect: The impact of high long-term PM2.5 on semantic memory exceeded the decline typically attributed to ten years of normal aging.
- Domain-specific findings: While semantic memory declined with higher pollution exposure, the study found no measurable associations between PM2.5 and executive function or verbal episodic memory.
- Focus on disparities: The STAR cohort was chosen to investigate environmental contributors to higher dementia rates among Black adults in the United States.
- Policy relevance: Because air pollution is a modifiable environmental exposure, reducing PM2.5 represents a practical prevention target to lower dementia risk at the population level.
- Individual risk reduction: The study reiterates practical measures individuals can use to reduce personal exposure to fine particulates.
Source: UC Davis
Overview
Researchers from UC Davis Health and Kaiser Permanente analyzed long-term PM2.5 exposure and cognitive performance using data from the STAR study. PM2.5 refers to airborne particles smaller than 2.5 micrometers—about 1/30th the diameter of a human hair. Prior research has linked PM2.5 to cardiovascular disease and mortality; this study examines its potential role in domain-specific cognitive decline, especially semantic memory.
“Semantic memory is essential for everyday communication and functioning,” said Kathryn Conlon, associate professor in the UC Davis Department of Public Health Sciences and senior author on the study. “These results suggest that long-term air pollution exposure may shape how the brain ages in ways that affect independence and quality of life.”
The study’s primary findings were published in Alzheimer’s & Dementia: Behavior & Socioeconomics of Aging.
Reducing air pollution may reduce dementia burden
The STAR study, launched in 2017, investigates factors that influence healthy brain aging among Black adults. Black adults in the United States face 1.5 to 2 times higher rates of Alzheimer’s disease and related dementias compared with non-Hispanic White adults. Because disadvantaged communities more often live with elevated particulate levels, understanding environmental contributors like PM2.5 is essential to addressing these disparities.
This study focused on PM2.5—fine particulate matter that can penetrate deep into the lungs and enter the bloodstream. Long-term exposure can vary by neighborhood, traffic patterns and other local sources, and previous work has shown elevated exposures in many racially and economically marginalized communities.
Methods and findings
The analysis included 740 adults aged 53 to 94 from the STAR cohort. Researchers estimated individual long-term PM2.5 exposure by averaging daily modeled PM2.5 levels at each participant’s home address over 5-, 10- and 17-year periods. Cognitive performance was measured across three domains—semantic memory, verbal episodic memory and executive function—and standardized as Z-scores.
After adjusting for age, sex, education, marital status and neighborhood income, higher long-term PM2.5 exposure over 17 years was linked with significantly lower semantic memory (β = −0.61 SD per 5 µg/m3, 95% CI: −1.03 to −0.19). Associations for the 5- and 10-year exposure averages showed similar but slightly reduced effects. The study detected no associations between PM2.5 and executive function or verbal episodic memory.
Key interpretations: the effect size for long-term PM2.5 on semantic memory was comparable to, and in this analysis exceeded, the decline expected from roughly ten years of normal aging. The domain-specific pattern suggests PM2.5 may impact particular brain systems more than others.
Lowering air pollution could lower Alzheimer’s burden
Because long-term PM2.5 exposure tends to be higher in under-resourced neighborhoods, reducing particulate pollution could help narrow disparities in dementia risk. Rachel Whitmer, co-author and co-director of the Alzheimer’s Disease Research Center at UC Davis Health, emphasized that air pollution is a modifiable risk factor and therefore an important prevention target for public health policy and community interventions.
How individuals can reduce exposure to air pollution
Although air pollution is fundamentally a community and policy issue, individuals can take steps to lower personal exposure to PM2.5:
- Monitor local air quality forecasts and advisories to avoid high-exposure days.
- Limit outdoor activities when particulate levels are elevated, including during wildfire smoke events.
- Use high-efficiency particulate air (HEPA) filters indoors to reduce indoor PM2.5.
- Keep windows closed on days with poor air quality.
- Avoid exercising near busy roads or heavy traffic corridors.
- Use recirculated air settings in vehicles during traffic congestion or smoky conditions.
Key Questions Answered
A: Semantic memory stores facts, word meanings and general knowledge that support communication and day-to-day decisions. Loss in this domain can erode independence and the ability to understand and interact with the world.
A: In this analysis, the reduction in semantic memory linked to 17 years of higher PM2.5 exposure exceeded the decline typically expected from ten years of normal aging.
A: The STAR cohort targets Black adults to investigate environmental and social drivers of the documented higher dementia rates in this population. Demonstrating links between pollution and cognition in this cohort informs equity-focused prevention strategies.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The journal article was reviewed in full and additional context was added by staff.
About this research news
Author: Lisa Howard
Source: UC Davis
Contact: Lisa Howard – UC Davis
Image: Image credited to Neuroscience News
Original Research: Open access. “Particulate air pollution and domain-specific cognition among Black adults” by Stacey E. Alexeeff, Chinomnso N. Okorie, Paola Gilsanz, Joel Schwartz, Amanda J. Goodrich, Ai-Lin Tsai, Rachel A. Whitmer, Kelly M. Bakulski, Scarlet Cockell, Kathryn C. Conlon. Alzheimer’s & Dementia: Behavior & Socioeconomics of Aging. DOI: 10.1002/bsa3.70074
Abstract
Particulate air pollution and domain-specific cognition among Black adults
INTRODUCTION
Long-term exposure to fine particulate air pollution (PM2.5) may affect cognitive function, but evidence from diverse cohorts with long-term exposure estimates has been limited.
METHODS
We analyzed data from 740 adults aged 53 to 94 in the Study of Healthy Aging in African Americans (STAR). Cognitive performance was assessed in three domains (semantic memory, verbal episodic memory, and executive function) and standardized to Z-scores. Using linear regression, we evaluated associations with 5-, 10-, and 17-year average PM2.5 exposure. Fully adjusted models included age, sex, marital status, education, and neighborhood income.
RESULTS
Greater long-term PM2.5 exposure over 17 years was associated with lower semantic memory (β = −0.61 SD, 95% CI: [−1.03, −0.19] per 5 µg/m3). Associations were similar but slightly attenuated for 5- and 10-year exposures. No associations were observed with executive function or verbal episodic memory.
DISCUSSION
Long-term PM2.5 exposure may contribute to lower semantic memory in midlife and later-life Black adults, highlighting an environmental pathway that could be targeted for dementia prevention and health equity efforts.