A massive long-running study has found a link between air pollution and an increased risk of dementia, concluding that even slightly higher levels of air pollution exposure over an extended period can significantly increase a person's risk of dementia.
Reported in the journal Environmental Health Perspectives, researchers from the University of Washington looked at decades' worth of data from two long-running projects, one on dementia risk factors and one on air pollution, in the coastal area of the Pacific Northwest.
In sum, they found that just a 1 microgram per cubic meter difference between residences was associated with 16 percent higher incidence of dementia. For context, you can expect to find a 1 microgram per cubic meter difference between a busy downtown street and a leafy suburb.
“We found that an increase of 1 microgram per cubic meter of exposure corresponded to a 16 percent greater hazard of all-cause dementia. There was a similar association for Alzheimer’s-type dementia,” Rachel Shaffer, lead author who conducted the research as a doctoral student in the University of Washington’s Department of Environmental & Occupational Health Sciences, said in a statement.
Of the more than 4,000 Seattle-area residents enrolled in the dementia study, some 1,000 were diagnosed with the neurological disorder since 1994 when the study began. Once a person with dementia was identified, the team looked at the levels of air pollution they were exposed to during their lifetime (bearing in mind air pollution levels have changed since the study kicked off) and compared the pollution exposure of other participants. This gave them an idea of how much air pollution contributed to their dementia diagnosis.
“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,” explained Shaffer.
The reason why air pollution has been linked to dementia time and time again is not perfectly understood, but scientists have started to get a clearer picture.
Air pollution is a concoction of gases, solids, and liquid particles. This can include a cocktail of toxic ingredients, such as nitrogen dioxide, sulfur dioxide, and carbon monoxide. While these are all worrying in and of themselves, the component that appears most concerning for the brain is particulate matter, microscopic particles that stem from smoke, dust, and exhaust pipes. These particles are so small they can easily infiltrate the human body, entering our bloodstream and even our brains, likely bringing along a host of toxic hitchhikers with them. Once inside the brain, the foreign particles trigger the body’s defenses and spark brain inflammation, which is known to be linked to neurodegeneration.
On top of dementia, air pollution has been found to have associations with other neurological problems, with some studies even linking air pollution to reduced intelligence.