Air pollution has long been known to be a contributing factor to a whole host of respiratory and cardiovascular conditions, but now a team at the University of Washington has provided evidence that poor air quality can significantly raise the risk of dementia.
The team compared data from the Kaiser Permanente Washington Health Institute’s Adult Changes in Thought, a study looking at the incidence of dementia that began in the 1990s, with detailed air pollution data dating back to the 1970s.
They concentrated on a type of pollution known as PM2.5 – particles or liquid droplets in the air with a diameter less than 2.5 micrometres, about 30 times finer than a strand of human hair.
They found that for each increase of 1 microgram per cubic meter of PM2.5 was linked to a 16 per cent greater risk of all-cause dementia. For comparison, air in the most polluted areas of London has around 15 micrograms per cubic metre of PM2.5.
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“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,” said lead author Rachel Shaffer, who conducted the research as a doctoral student in the UW Department of Environmental & Occupational Health Sciences.
“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.”
While there are many other factors that are associated with an increased risk of dementia such as diet, exercise and genetics, the team say air pollution should now be recognised as a key contributing factor and that reducing people’s exposure to air pollution could help reduce the burden of dementia.
“Over an entire population, a large number of people are exposed. So, even a small change in relative risk ends up being important on a population scale,” Shaffer said.
“There are some things that individuals can do, such as mask-wearing, which is becoming more normalised now because of COVID. But it is not fair to put the burden on individuals alone. These data can support further policy action on the local and national level to control sources of particulate air pollution.”