Air Pollution Tied to Signs of Alzheimer’s in Brain Tissue, Study Finds

Bonnie Jo Mount/The Washington Post
The Suncor Energy oil refinery outside Denver in 2018.

People who inhale higher concentrations of tiny airborne particulates, like from diesel exhaust or other traffic-related air pollutants, are more likely to have signs of Alzheimer’s disease in their brains, according to a new study, the latest in a growing body of research that shows a link between air pollution and cognitive decline.

For the study, published this week in the journal Neurology, researchers examined the association between concentrations of ambient air pollution and signs of Alzheimer’s disease in the human brain. They found that people who were exposed to higher concentrations of fine particulate matter air pollution, also known as PM2.5, at least a year before their death were more likely to have higher levels of plaques – abnormal clusters of protein fragments built up between nerve cells, which is a sign of Alzheimer’s in brain tissue. The research also found a strong association between the pollution and signs of the disease for people who were not already genetically predisposed to Alzheimer’s.

“This suggests that environmental factors like air pollution could be a contributing factor to Alzheimer’s disease, especially in patients in which the disease cannot be explained by genetics,” said Anke Huels, the lead author of the study and an assistant professor at Emory University’s School of Public Health. While the study does not prove that air pollution causes Alzheimer’s disease, it found an association between exposure to specific kinds of pollution and signs of the disease.

Researchers examined tissue from 224 donors in Atlanta’s metropolitan area who, before their deaths, volunteered to donate their brains to research.

“Donors who lived in areas with particularly high levels of traffic-related air pollution showed more plaques related to Alzheimer’s disease at death than donors who lived in areas with lower air pollution concentrations,” Huels said.

What that told researchers, she added, is that being exposed to high levels of the pollution increases your risk for Alzheimer’s disease.

More than half of the donors had what’s known as the APOE gene, the strongest genetic risk factor for Alzheimer’s disease. But for the donors who were not already genetically predisposed, researchers found a stronger association between traffic-related air pollution and signs of Alzheimer’s disease.

It’s long been known that concentrations of PM2.5 can trigger short-term respiratory problems. That’s because the particulates are so small – measuring 2.5 microns and smaller in diameter – that they enter the bloodstream after being inhaled. Breathing in smoke can also irritate your sinuses, throat and eyes, according to the Centers for Disease Control and Prevention. In more severe cases, exposure is linked to cardiovascular impacts – including heart attacks and stroke – as well as lung cancer and damage to cognitive functions.

Gaurab Basu, the director of education and policy at Harvard’s center for climate, health and the environment, said the study shines a spotlight on ambient air pollution’s dangers to the brain.

“We often think about air pollution in the lungs, but it’s critical that we put the brain at the forefront of the conversation of the ways that air pollution impacts our health,” Basu said.

While this study primarily examined the brains of White, college-educated men, Basu said poorer communities and communities of color are often more exposed to particulate matter and traffic-related pollution – because highways and roadways are intentionally built in their communities.

“This pollution does not impact everyone the same,” Basu said. “Vehicular air pollution is fundamentally an issue of health equity.”

More research is needed to determine the exact connection between traffic-related air pollution and the brain changes of Alzheimer’s disease, said Heather Snyder, the Alzheimer’s Association vice president of medical and scientific relations.

“We know that Alzheimer’s is a complex disease, and it is likely that there are a variety of factors, in combination, that impact a person’s lifetime risk,” Snyder told The Post in an email. “Avoiding exposure to air pollution is a risk factor that some people can change, but others can’t, or can’t so easily.”

This study is also just the latest in the growing literature revealing associations between ambient air pollution and cognitive decline. Emerging research has also found that exposure to traffic-related fine particulate matter is correlated with reduced cortical thickness and thinner gray matter in the brain, which may influence information processing, learning and memory. Experts pointed to mounting evidence that links exposure to air pollution with cognitive decline, mood disorders and diagnoses of Alzheimer’s disease.

To Huels, the best way to mitigate exposure is to make individual changes such as limiting time outdoors when air pollution concentrations are high and wearing a mask when appropriate. She said other changes such as driving an electric vehicle or taking public transportation can contribute to reducing air pollution.

“To really reduce air pollution exposures, we need political decisions and changes,” Huels said. “There really isn’t a safe or healthy level of air pollution in general or traffic related air pollution.”