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August 14, 2023

Pollution from wildfires linked to greater risk of dementia, study finds

New research examines long-term exposure to fine-particulate matter; its results also reaffirm concerns about environmental racism

Long-term exposure to pollution from wildfires increases the odds of patients developing dementia, new research has found.

Scientists have already found some evidence that air pollution is linked to dementia, but the new study, published Monday in the Journal of the American Medical Association, looked at specific sources of pollution. While the fine particulate matter from road traffic and coal-powered plants presented risks, only pollution from agriculture and wildfires was "robustly associated with greater rates of dementia."

MORE: Philly hospitals pledge to no longer consider a patient's race in certain treatment guidelines

The study examined 27,857 Americans over the age of 50, drawn from an existing study of older adults in the U.S. During their first interview, none of the participants had dementia. But when they were interviewed again between 10-18 years later, researchers found that 15% had developed dementia — and people who did often lived in neighborhoods where they were exposed to higher levels of fine particulate matter.

Compared with those who did not develop dementia, the participants who did were more likely to be Black or Hispanic, emphasizing existing concerns about the impact of environmental racism on public health.

The study authors estimate nearly 188,000 new cases of dementia every year can be linked to air pollution exposure. While air pollution from wildfires has long been a concern for the West Coast and Pacific Northwest, the raging fires in Canada and now Hawaii this summer have exposed new populations to fine particulate matter, the long-term health impacts of which are still not fully understood.

More immediate health effects attributed to wildfire smoke include coughing, wheezing, difficulty breathing, irritation of the eyes and overall reduced lung function. Short-term exposure can also exacerbate preexisting conditions, like asthma or cardiovascular disease, increasing the risk of a hospital visit.

"Although individual wildfires may be short-lived, they have become more frequent and destructive in the past decades because of warmer temperatures, earlier spring snowmelt, and longer fire seasons," the researchers wrote. "Additionally, although the precise locational origin of wildfires may vary, the long-range smoke from wildfires frequently impacts the same downwind locations, resulting in wildfire smoke becoming a more long-term presence; many US cities now experience more than 30 days affected by smoke each year."

Philadelphia was one of several cities impacted by smoke from Canadian wildfires in recent months. At the beginning and end of June, the city issued air quality alerts urging residents to take caution by remaining indoors and wearing N95 masks when outside. Some outdoor events, including Phillies games, were postponed as the air quality levels climbed, at one point even reaching Code Maroon, the worst category on the U.S. air quality index.

Code Maroon indicates an AQI greater than 300. By comparison, the AQI in Philadelphia on Monday morning was around 52, which is slightly in the moderate range.

The agricultural industry, the other source of pollution that researchers "robustly" linked to dementia, is a significant contributor to air pollution, especially fine-particulate pollution generated by fertilizer use, animal waste and industrial machinery. One study in 2021 says air pollution from animal agriculture can be blamed for 17,900 deaths per year in the United States.

The study's authors conclude that preventive actions, from personal air purifiers to government environmental regulations, may be necessary to reduce rates of dementia and promote healthy cognitive aging.  

Correction: A previous version of this story said most of the study participants who developed dementia were not white. The participants who developed dementia were more likely to be Black or Hispanic when compared with those who did not develop the disease.

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