By comparing data from two studies, researchers have identified a potential link between air pollution and dementia.
The data was compiled from two large, long-running studies in the Puget Sound region. One study began in the late 1970s examining air pollution and the other began in 1994 analysing risk factors for dementia.
The study
A small increase in fine particle pollution levels was detected (PM2.5 or particle matter 2.5 micrometres or smaller) at specific addresses in the Seattle area. This was associated with a greater risk for dementia for those living in that area.
The research examined 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-Seattle.
It revealed that more than 1000 of the participants had been diagnosed with dementia at some point since 1994. Once the patients with dementia were identified, researchers compared the average pollution exposure leading up to the age of diagnosis. For example, if a patient was diagnosed at 72 then researchers compared the pollution exposure of the 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 addition to the extensive air pollution and dementia rates for the region, other strengths included lengthy address histories and high-quality procedures for dementia diagnosis for participants. The reliable address histories meant researchers could obtain more precise pollution estimates.
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Results
In the final analysis, the researchers found that just 1 microgram per cubic meter difference between residences was associated with a 16 per cent higher incidence of dementia.
There are many factors associated with increased dementia risks such as diet, exercise and genetics. Air pollution is now recognised to be one key potentially modifiable risk factor. The study findings add to a body of evidence suggesting that reducing exposure to air pollution could reduce the dementia risk.
The researchers suggest that small changes can be important on a larger scale such as mask-wearing. However, they highlight the need for policy action on a national and local level.
Lead author Rachel Shaffer, a doctoral student at UW Department of Environmental & Occupational Health Sciences said: “We found that an increase of 1 microgram per cubic meter of exposure corresponded to a 16 per cent greater hazard of all-cause dementia. There was a similar association for Alzheimer’s-type dementia,”
She added: “We know dementia develops over a long period of time. It takes years – even decades – for these pathologies to develop in the brain, and so we needed to look at exposures that covered that extended period. Because of long-running efforts by many UW faculty and others to build detailed databases of air pollution in our region, “we had the ability to estimate exposures for 40 years in this region. That is unprecedented in this research area and a unique aspect of our study.”
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