Summary: Recent research has linked air pollution, especially fine particulate matter (PM2.5), to higher risks of Alzheimer’s disease and cognitive decline. New findings indicate that reductions in atmospheric fine particulates and improved air quality may lower the risk of Alzheimer’s and other dementias.
Source: USC
Two USC researchers who previously connected air pollution with increased Alzheimer’s risk and accelerated cognitive decline report evidence that cleaner air can benefit brain health.
Vehicle exhaust and industrial emissions create a form of fine particulate pollution known as PM2.5. These particles, smaller than the width of a human hair, can be inhaled and travel from the nasal passages into the brain, bypassing the blood-brain barrier that normally shields the brain from many environmental contaminants. Over time, long-term exposure to PM2.5 has been associated with premature death and worsened outcomes in people with chronic heart or lung disease.
In a research letter published in Alzheimer’s & Dementia, University Professor Caleb Finch and associate professor Jennifer Ailshire, both at the USC Leonard Davis School of Gerontology, describe parallel findings from their independent laboratories showing reduced neurotoxicity of PM2.5 in recent years in both human and mouse studies.
Ailshire’s analysis of nationwide data from the Health and Retirement Study, published earlier in the Journal of Alzheimer’s Disease, showed a strong association between elevated PM2.5 exposure and cognitive deficits among adults aged 65 and older who had fewer than eight years of education in 2004. When she reexamined the same population a decade later, that association was no longer apparent.
Ailshire attributes the change largely to improved air quality: average annual PM2.5 levels in participants’ neighborhoods were about 25% lower than they were in 2004. By 2014, few participants lived in areas where annual PM2.5 exceeded U.S. Environmental Protection Agency standards, suggesting that reductions in high pollution exposure corresponded with fewer pollution-related cognitive deficits among older adults.
“Improving air quality around the country has been a major public health success,” Ailshire said, “but recent trends are worrying. Pollution levels have begun to rise again in some regions, and large wildfires are producing significant episodic spikes in air pollution. These developments could threaten progress in reducing pollution-related brain health risks.”
Finch’s laboratory reported complementary results in mice, also published earlier this year in the Journal of Alzheimer’s Disease. His team has exposed mice to urban air pollution measured at a Los Angeles research site since 2009. After 2017, mice exposed to a nanoscale component of PM2.5 showed clear signs of improved neurological health, with substantial declines in markers of neurotoxicity such as oxidative damage to cells and tissue.
While nationwide PM2.5 levels fell substantially—by about 41% from 2000 to 2020 according to EPA data—the pattern was not uniform across all regions. Urban PM2.5 in Los Angeles decreased only slightly between 2009 and 2019, and ozone levels that had been trending down nationally reversed in Los Angeles County after 2015. These regional differences underscore that air quality improvements are uneven and potentially reversible.
Finch and Ailshire caution that their recent findings do not prove that air quality improvements directly reduce dementia incidence, but they do suggest that declining PM2.5 toxicity correlates with better brain health indicators in both experimental and population studies. The observed year-over-year increases in some pollution measurements since 2017 highlight that gains in air quality can be undone and must be actively preserved.
“These results reinforce the importance of continued efforts to reduce air pollution and of ongoing research into how air pollution affects the aging brain,” Finch said.
Finch and Jiu-Chiuan “J.C.” Chen of the Keck School of Medicine previously combined human and animal data to show that air pollution-related brain aging processes may raise dementia risk. Their earlier research found that older women living in areas with high PM2.5 experienced memory loss and Alzheimer’s-like brain atrophy not seen in women living with cleaner air, pointing to a potential pathway linking pollution exposure to neurodegeneration.
About this pollution and dementia research news
Author: Jenesse Miller
Source: USC
Contact: Jenesse Miller – USC
Image: The image is in the public domain
Original Research: The findings will appear in Journal of Alzheimer’s Disease