Air pollution can cause more signs of Alzheimer’s in the brain

PM2.5 Exposure linked to Alzheimer's Disease pathology in brain donors.

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A new study in the American Academy of Neurology medical journal found that people highly exposed to traffic-related air pollution were likelier to have more brain amyloid plaques. The researchers found particulate matter called PM2.5, including tiny air pollutant particles. The study did not clear that air pollution directly causes amyloid plaques in the brain; it just shows a connection between them.

Study author Anke Huels, Ph.D., of Emory University in Atlanta, said, “These results add to the evidence that fine particulate matter from traffic-related air pollution affects the amount of amyloid plaque in the brain. More research is needed to investigate the mechanisms behind this link.”

In this study, researchers studied the brain tissue of 224 people who agreed to donate their brains after they died to help dementia research. These individuals had an average age of 79 at the time of death.

The researchers focused on the air pollution from traffic near people’s homes in Atlanta when they passed away. Traffic-related PM2.5, a type of air pollution, is a big problem in cities like Atlanta, where most donors live. 

On average, this pollution level was 1.32 micrograms per cubic meter (µg/m3) in the year before their death and 1.35 µg/m3 in the three years leading up to their end. The researchers compared pollution levels and signs of Alzheimer’s Disease in the brain, like amyloid plaques and tau tangles. 

They found out that people exposed more to air pollution one and three years before they died were more likely to have higher levels of amyloid plaques. The likelihood of higher plaque levels nearly doubled for every 1 µg/m3 increase in PM2.5 exposure in the year before death. Similarly, higher exposure in the three years before death increased the likelihood of higher plaque levels by 87%.

In addition, the researchers checked if having the primary gene linked to Alzheimer’s, APOE e4, affected the connection between air pollution and Alzheimer’s signs in the brain. They found that the link between air pollution and Alzheimer’s symptoms was strongest among those who didn’t have the gene variant.

Huels explained, “This suggests that environmental factors such as air pollution could be a contributing factor to Alzheimer’s in patients in which the disease cannot be explained by genetics.”

The limitations of this study are that researchers only knew where people lived when they passed away, which might not accurately affect their exposure to pollution. In addition, the study mainly included white, educated individuals, so the findings might not apply to other groups.

Journal reference:

  1. Grace M. Christensen, Zhenjiang Li, et al., Association of PM2.5 Exposure and Alzheimer Disease Pathology in Brain Bank Donors—Effect Modification by APOE Genotype. Neurology. DOI: 10.1212/WNL.0000000000209162.
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