Aug. 15, 2023 – About 188,000 new dementia cases annually may be linked to exposure to air pollution, according to new research from the University of Michigan. Older people who live in places with high levels of agricultural or wildfire air pollution are at a particularly increased risk.
The study was published Monday in the journal JAMA Internal Medicine. It linked 18 years of data about people’s health to air pollution levels at the residential address of each of the nearly 28,000 people studied. None of them had dementia at the beginning of the research, their average age was 61 years old, and 57% were women.
Among all of them, 15% developed dementia within an average period of 10 years, but those who lived in areas with high levels of pollution were 8% more likely to develop dementia. (Dementia refers to a group of brain disorders that impact thinking, memory, language, and problem-solving. Alzheimer’s disease is the most common type of dementia.)
The researchers examined dementia risk levels based on different types of pollution exposure, including exposure to agricultural, traffic, coal combustion, and wildfire pollution.
The greatest risks of developing dementia were observed among people who lived in areas with high levels of agricultural air pollution or wildfire air pollution. Agricultural exposure was linked to a 13% increased risk of dementia, and wildfire exposure was linked to a 5% increased risk.
"In our study, we used a sophisticated prediction model that includes information about the chemical transformations and dispersion of pollution from different sources to estimate the levels of source-specific particulate matter air pollution at participants’ residential addresses," researcher Boya Zhang, a doctoral student who specializes in studying cognitive impacts of pollution, said in a statement. "This approach is beneficial because it not only accounts for pollution directly emitted by a source, but also pollution generated through reactions with other chemicals in the air."
Particulate matter from wildfires is so small that it can enter the brain directly through the nose or break through the brain-blood barrier in other ways. The findings are important because exposure to neurotoxic air pollution is considered “modifiable,” meaning that people’s exposure to pollution can be reduced or pollution itself can be reduced.
"These findings are quite timely given the increasing frequency of wildfire smoke in our communities," researcher Sara Adar, ScD, an associate professor of epidemiology, said in a statement. "Our data suggest that in addition to some of the more obvious health impacts of wildfire smoke, like irritation to our throats and eyes along with breathing difficulties, high smoke days might also be taking a toll on our brains."
"Our findings indicate that lowering levels of particulate matter air pollution, even in a relatively clean country like the United States, may reduce the number of people developing dementia in late life," Adar said.