A new study from the University of Southern California suggests that the pollution people inhale every day may affect brain health.
Researchers linked common outdoor pollutants to differences in brain areas associated with Alzheimer's disease.
Here's what to know
According to a USC news release, scientists at the university's Keck School of Medicine compared brain scans with estimated residential pollution exposure for 1,484 adults who had no dementia and no history of stroke.
Their analysis centered on two outdoor pollutants tied to combustion: fine particulate matter (PM2.5) and nitrogen dioxide (NO2). By using residential histories, researchers estimated participants' exposure to both pollutants during the three years leading up to later MRI scans.
In the group of women participants, higher estimated exposure to both pollutants was linked to reduced cortical thickness in four brain regions seen as especially vulnerable to Alzheimer's disease.
For PM2.5, every additional microgram per cubic meter corresponded to a cortical-thickness difference roughly equal to 13 months of aging. For NO2, each additional part per billion was associated with a difference similar to about three months of aging.
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The pattern in the group of male participants ran in the opposite direction. Higher pollution exposure was associated with a thicker cortex in the same regions, though that relationship weakened with age and appeared to reverse after about age 65.
More background
Memory, language, and decision-making depend heavily on the cortex, the brain's folded outer layer. Although this layer normally becomes thinner over time, unusually rapid thinning in certain regions can signal that brain cells are deteriorating.
These findings underscore brain health as an air pollution concern alongside established effects on the lungs and heart. Meanwhile, lead author Lauren Salminen, an assistant professor of research neurology at USC, said the findings suggest the connection may not be simple.
"Our findings raise the possibility that pollution-related brain changes are not linear," Salminen said in the release. "A thicker cortex at one point in life could represent an early biological response, while thinning later in life could reflect accumulated damage."
Because this study captured only a single point in time instead of following people over many years, it cannot prove that pollution caused the brain changes. Further research will be needed to better understand the connections between air pollution and its potentially different impacts across age and gender.
What can be done?
People can reduce exposure, especially near traffic-heavy areas, by checking the air quality index before spending long periods outdoors, choosing walking or running routes away from busy roads, and improving indoor air quality.
Filtering the air where you sleep may be especially helpful, since bedrooms are where many people spend a significant portion of their time. Approved HEPA air purifiers and better ventilation can reduce indoor buildup from outdoor pollution as well as household sources.
But this isn't an issue best managed at the individual level. Air pollution is shaped by vehicle standards, energy systems, industrial regulations, city planning, and public policy. And those most vulnerable to poor air quality are often living in low-income neighborhoods, marginalized from health systems, or dependent on outdoor work that may bring extra risks.
"Air pollution is a widespread and potentially modifiable risk factor that affects people across entire communities," Arthur Toga, a study co-author and a director at Keck, said in the release. Toga continued, "Understanding when these changes begin and how they evolve could ultimately help guide more effective approaches to protecting brain health."
Where can I learn more?
If you want to learn more about how polluted air could affect the brain, you may want to read these stories next:
• Traffic-heavy neighborhoods have been linked to severe cognitive decline and higher dementia risk.
• Among Danish nurses, long-term air pollution exposure has been tied to brain inflammation and dementia.
• In Scotland, older adults' past exposure showed how air pollution shaped dementia risk.
Routine air pollution may affect brain health through several overlapping pathways. The bigger picture helps explain why cutting exposure could matter years before symptoms show up.
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