Researchers have identified a link between air pollution and a greater hazard of all-cause dementia. They found a similar association for Alzheimer’s-type dementia.

The team from the University of Washington used data from two large, long-running study projects in the Puget Sound region—one that began in the late 1970s measuring air pollution and another that began in 1994 on risk factors for dementia.

The findings show a small increase in the levels of fine particle pollution (PM2.5 or particulate matter 2.5 micrometers or smaller) averaged over a decade at specific addresses in the Seattle area was associated with a greater risk of dementia for people living at those addresses.

“We found that an increase of 1 microgram per cubic meter of exposure corresponded to a 16% greater hazard of all-cause dementia. There was a similar association for Alzheimer’s-type dementia,” says Rachel Shaffer, who conducted the research as a doctoral student in the environmental & occupational health sciences department and is lead author of the paper in Environmental Health Perspectives.

Researchers looked at more than 4,000 Seattle-area residents enrolled in the Adult Changes in Thought (ACT) Study run by Kaiser Permanente Washington Health Research Institute in collaboration with the University of Washington. Of those residents, the researchers identified more than 1,000 people who diagnosed with dementia at some point since the ACT Study began in 1994.

Once researchers identified a patient with dementia, they compared the average pollution exposure of each participant leading up to the age at which the dementia patient was diagnosed. For instance, if a person was diagnosed with dementia at 72 years old, the researchers compared the pollution exposure of other participants over the decade prior to when each one reached 72.

In these analyses, the researchers had to account for the different years in which these individuals were enrolled in the study, since air pollution has dropped dramatically in the decades since the ACT study began.

In their final analysis, the researchers found that just a 1 microgram per cubic meter difference between residences was associated with 16% higher incidence of dementia. To put that difference into perspective, Shaffer says, in 2019 there was approximately 1 microgram per cubic meter difference in PM2.5 pollution between Pike Street Market in downtown Seattle and the residential areas around Discovery Park.

Read the full article about air pollution and dementia by Jake Ellison at Futurity.