Air pollution may not just be harmful to your lungs and respiratory health. Breathing in fine dust pollution known as particulate matter may also contribute to changes in the brain linked to Alzheimer’s disease.
A new study, carried out by researchers at the University of Southern California (USC), focused on 998 women in their 70s and 80s who had been exposed to varying levels of air pollution. Using data from the Women’s Health Initiative, the researchers tracked brain scans of the women five years apart, as well as measured their levels of exposure to air pollution.
The women who were exposed to more air pollution in the five years between brain scans had a higher likelihood of developing visible changes in their brains. In particular, the researchers identified atrophy, or the brain getting smaller, as one of the main changes.
“We found that the air pollution was contributing to atrophy or parts of the brain getting smaller over the five years,” said Andrew Petkus, assistant professor in the department of neurology at USC and an author of the study, said in an interview with Being Patient. “So women who were exposed to higher levels of air pollution had greater atrophy in those important brain areas associated with Alzheimer’s disease.”
Even when the researchers adjusted for important factors associated with Alzheimer’s—like age, cardiovascular health, clinical status, racial background and lifestyle such as smoking or exercise, “We still found that this association [between air pollution and brain changes] persisted,” Petkus said.
Petkus noted that past research had identified a link between pollution and changes in certain regions of the brain, such as the hippocampus, which are associated with memory.
One 2018 study reported that air pollution increased a person’s risk of developing dementia by 40 percent. Another study found that exposure to air pollution could cause changes in the brain at a much younger age than imagined—even in babies.
Particulate Matter and the Brain
The small type of particulate matter, known as PM2.5, is one of the most hazardous types of air pollution. Traffic fumes, dust and smoke billow PM2.5 into the air, and the tiny size of these particles allows them to enter a person’s lungs easily and get lodged there.
Particulate matter has been linked to an increased risk of asthma, cardiovascular disease and respiratory illnesses. But how do these miniscule particles travel into the brain?
“There are a few hypotheses,” said Petkus. “One is that not only does the particulate matter go into your lungs, but it goes into your bloodstream and reaches your brain that way. When we directly inhale it through our nose, it can go directly into our brain.”
He added that past studies in mice showed that once particulate matter was in the system, it can cause an inflammation and immune response. Inflammation has been identified as one major driver of Alzheimer’s and other neurodegenerative diseases.
Reducing Exposure to Air Pollution
Petkus notes that he hopes continued research into the link between air pollution and cognitive health will have “important policy implications.”
“It’s necessary to continue enforcing Environmental Protection Agency (EPA) guidelines and standards,” Petkus said. “Doing this could have important implications in decreasing risks for memory decline.”
As for the individual, there’s not much one can do to clean the air. But you can reduce your risk of exposure to air pollution by staying indoors on days when there are air pollution advisories.
“You can’t just move from your house to somewhere where there’s low air pollution,” Petkus said. “I think one of the important things this can be helpful for, however, is education—that air pollution is a risk factor. On days when air pollution is higher, avoid going outside or at least try to minimize exposure outdoors.”
Further research will involve a deeper look at the interplay between exposure to air pollution and the risk for depression, as well as cognitive decline, later in life, Petkus said. Exploring the nuances of how pollution affects cognition—from emotional regulation to memory decline—can help researchers better understand how to protect people from environmental factors.