Air pollution may be harming your brain’s ‘encyclopedia’

A new study by researchers at UC Davis Health and Kaiser Permanente found that higher exposure to very small air pollution particles (PM2.5) over a 17-year span was associated with lower semantic memory. Semantic memory acts like the brain's "encyclopedia" for things like facts, words and long-term general knowledge.

"Semantic memory is essential for communication, comprehension and navigating everyday life," said senior author Kathryn Conlon, an associate professor in the UC Davis Department of Public Health Sciences. "Our findings suggest that long-term exposure to air pollution doesn't just affect physical health - it may also shape how the brain ages, particularly in ways that matter for independence and quality of life."

Two other measures of cognitive function - executive function and verbal episodic memory - did not show an impact related to the pollution.

The findings were published in Alzheimer's & Dementia: Behavior & Socioeconomics of Aging.

Reducing air pollution may reduce dementia burden

The data for the research comes from the Kaiser Permanente Study of Healthy Aging in African Americans (STAR). Launched in 2017, the ongoing study aims to identify factors that impact healthy brain aging among Black adults.

Black adults in the United States experience 1.5 to 2 times higher rates of Alzheimer's disease and other dementias compared with non-Hispanic White adults.

In the new study, the researchers focused on particulate matter (PM), a mixture of solid particles and liquid droplets found in the air. Particles less than 2.5 micrometers in diameter (about 1/30th of a human hair) are referred to as PM2.5_, or fine particulates.

Previous research has linked PM2.5 to cardiovascular disease and mortality; however, a growing area of study is focused on the role of fine particulate exposure in the progression of Alzheimer's disease.

Methods and findings

The researchers analyzed data from 740 adults, aged 53 to 94, who were participants in the STAR study. Individual-level long-term average PM2.5 exposures were computed by averaging daily estimates of PM2.5 levels at the participants' residential addresses.

Cognitive performance was assessed for semantic memory, verbal episodic memory and executive function. They evaluated associations with 5-, 10-, and 17-year average PM2.5 exposure.

The researchers found:

• People who were exposed to higher levels of PM2.5 pollution over many years scored noticeably lower on semantic memory tests than those exposed to lower levels of pollution.
• The association with PM2.5 pollution persisted even after accounting for other factors such as age, education, income and marital status.
• The effect of long-term PM2.5 exposure on semantic memory was greater than what researchers would expect from 10 years of normal aging.

Lowering air pollution could lower Alzheimer's burden

Long-term exposure to air pollution has been shown to cause greater harm to under-resourced communities. In addition, studies led by the U.S. Environmental Protection Agency (EPA) have found that people who are Black, Latino or Asian are more likely to live in areas with higher levels of particulate air pollution.

"Understanding environmental contributors to cognitive decline is critical for addressing disparities in dementia risk," said Rachel Whitmer, co-author of the study and the co-director of the Alzheimer's Disease Research Center at UC Davis Health. "Air pollution is a modifiable exposure. That makes it a powerful target for prevention - both at the individual level and through public policy."

How individuals can reduce exposure to air pollution

While air pollution is largely a community-level issue, there are many ways individuals can reduce their exposure to air pollution:

• Check daily air quality forecasts on AirNow. The EPA website lets you enter your ZIP code to find out about air quality, which accounts for fine particulates, in your area.
• Limit outdoor activity when pollution levels are high, especially during wildfire smoke events.
• Use high-efficiency (HEPA) air filters indoors.
• Keep windows closed on poor air quality days.
• Avoid exercising near busy roads or heavily trafficked areas.
• Use recirculated air settings in vehicles during heavy traffic or smoky situations.

Funding

The study with Kaiser Permanente was funded by grants to the University of California, Davis, from the National Institutes of Health National Institutes on Aging (R01AG074347, R01AG050782)

A full list of authors is available in the study.

Resources

• Read the study