Long term exposure to air pollution may accelerate brain aging in regions vulnerable to Alzheimer's disease, according to researchers from the University of Southern California.
The study, published in the peer-reviewed journal NeuroToxicology, analyzed magnetic resonance imaging (MRI) brain scans from 1,484 individuals without a history of dementia or stroke while evaluating local air quality in their residential areas.
Scientists focused on concentrations of fine particulate matter known as PM2.5 and nitrogen dioxide (NO2), two of the most prevalent air pollutants produced by vehicle emissions, power generation plants, and industrial fuel combustion.
Impact on older women
Among older women, higher exposure to both pollutants was associated with a pronounced thinning of the cerebral cortex in brain regions responsible for memory. These specific areas are known to be especially vulnerable to damage from Alzheimer's disease.
Researchers calculated that each additional microgram of PM2.5 per cubic metre of air was linked to cortical changes equivalent to approximately 13 months of natural brain aging. For nitrogen dioxide, a similar increase in exposure corresponded to roughly three months of brain aging.
PM2.5 refers to airborne particles measuring 2.5 micrometres or smaller in diameter, which can enter the respiratory system and circulate throughout the body. Nitrogen dioxide is a toxic gas formed when fossil fuels burn at high temperatures, making both contaminants common features of urban environments.
Different effects in younger men
In contrast to the findings in older female participants, researchers observed an opposite pattern among younger men. Higher air pollution exposure in this group was linked to a structural thickening of the same cortical areas.
The cerebral cortex is the outermost layer of neural tissue in the brain, responsible for essential cognitive functions including memory, thought processing, language, and sensory perception. Structural alterations in its thickness are widely monitored by neuroscientists as key indicators of brain health and cognitive decline.
The study authors emphasized that their findings demonstrate a statistical association rather than direct causation. The research does not prove that air pollution directly causes structural brain alterations or increases an individual's overall risk of developing Alzheimer's disease.
Broader context in dementia research
Alzheimer's disease is a progressive neurological disorder that leads to irreversible memory loss and cognitive impairment. Environmental and lifestyle factors have increasingly become the focus of neurodegenerative research alongside genetic risks.
Earlier scientific studies have highlighted other early life interventions in brain health, including findings that limiting sugar consumption during a child's first 1,000 days of life reduces the long-term risk of developing Alzheimer's disease.
The University of Southern California team noted that further research is needed to determine the biological mechanisms through which ambient pollutants interact with neural tissue across different age groups and genders.
