Long-term study links air pollution exposure to dementia risk

There’s a growing body of evidence that chronic exposure to fine particulate matter (PM_2.5) increases the risk of neurological diseases, including Alzheimer’s disease and other kinds of dementia. Most studies linking PM_2.5 to dementia were conducted over relatively short periods of up to 5 years. But researchers believe dementia develops over a longer time.

That’s why researchers led by Rachel Shaffer, a graduate student at the University of Washington, wanted to study risk over 10 years. They found that among a cohort of 5,546 adults in the Seattle area, for every additional microgram of PM_2.5/mm³ of air a person was exposed to over the course of a decade, the risk of developing dementia increased 16% (Environ. Health Perspect. 2021, DOI: 10.1289/EHP9018). They estimated air pollution exposure based on participants’ home addresses.

The risk her team found is higher than that found in shorter-term studies, Shaffer says. That could be because they were done in different parts of the world, where the chemical composition of PM_2.5—and its health risks—may be different. She also notes that dementia diagnoses in the Seattle study were based on detailed cognitive assessments performed every 2 years rather than on the administrative data, such as health insurance records, used in other studies.

In the absence of treatments for dementia, Shaffer says, the best approach is prevention. “You can’t change your genetics, but air pollution is a modifiable risk,” she says. Still, she says the burden shouldn’t fall on individuals. Data from this study support policies that would reduce ambient PM_2.5 levels at a population scale.