Study Shows Physical Changes in the Brain After Long-Term Exposure to Traffic Pollution Related to an Increased Risk of Alzheimer’s Disease

By Kelly Jordan 

Exposure to traffic-related air pollution has been linked to dementia, Alzheimer’s disease, and other examples of cognitive decline (people’s thinking, memory, and learning abilities). Determining the physical changes to people’s brains when they are exposed to traffic-related air pollution, especially fine particulate matter (PM2.5), and who is at greatest risk, is something researchers have been working hard to understand. 

New Insights into Traffic Pollution Exposure and Brain Health

A new Emory-led study, which analyzed 224 brains donated to the Goizueta Alzheimer's Disease Research Center, provided major contributions to this puzzle. Findings were published in Neurology and Alzheimer's & Dementia: The Journal of the Alzheimer's Association and include:

• Huels and colleagues found an association between traffic-related air pollution exposure and indications of Alzheimer's disease in brain tissue. Traffic-related PM2.5 exposure was associated with a higher CERAD score. The CERAD score is used to measure β-amyloid (Aβ) plaques in the brain, which are related to the progression of Alzheimer’s disease. This contributes to a growing body of evidence that PM2.5 affects the deposition of amyloid plaques in the brain, which is a hallmark of Alzheimer's disease.
• The association between PM2.5 and Alzheimer’s disease was particularly strong among donors without APOE ε4 alleles, which is the strongest known risk factor for Alzheimer’s disease. This suggests that environmental factors like air pollution could be a contributing factor to Alzheimer’s disease in patients in which the disease cannot be explained by genetics.
• Differences in the epigenome of the brain (specifically, DNA methylation patterns) were related to people’s traffic-related air pollution exposure based on where they lived. Epigenetics is the study of how your environment can cause changes that affect the way your genes work. These findings further highlight the physical changes in the brain in response to air pollution exposure, which can consequently be linked to Alzheimer’s disease progression.

What This Means for Public Health Knowledge

“Few autopsy cohorts have large enough sample sizes with personal information to investigate associations between these neuropathologies and environmental factors like air pollution,” says Anke Huels, PhD, last and corresponding author on both articles.

“We established for the first time a potential mediation effect of DNA methylation for the association between PM2.5 and neuropathological changes of Alzheimer's disease. These findings bring us one step closer to understanding the biological mechanisms underlying the association between air pollution exposure and the development of Alzheimer's disease.

"While our findings are important, they are just one additional piece in the puzzle connecting air pollution with Alzheimer’s disease. We need more evidence from larger autopsy cohorts and prospective cohort studies with repeated cognitive tests and biomarkers of Alzheimer’s disease to fully understand how air pollution affects our brain.”