Wildfire smoke increases risk of dementia, study finds

The wildfire smoke that blankets much of the American West each summer is likely more harmful than previously understood, especially to older people, scientists found.

Research announced this week, and led by scientists at the University of Washington, discovered that prolonged exposure to the ultrafine particles in wildfire smoke heightens the risk of dementia for those 60 and older.

That risk will continue to rise as climate change warms the atmosphere and deepens wildfire seasons, said lead author Joan Casey, an environmental epidemiologist at the University of Washington.

Not only are older people at risk with the increasing exposure to wildfire smoke but so too are those who can't access air quality warnings, afford filtration or avoid outdoor exposure throughout the fire season, she said.

"This is yet another example of climate change impacting disadvantaged communities first and worst," Casey said.

For the study Casey partnered with scientists from the University of Pennsylvania, Columbia University, the University of California in San Diego, Los Angeles and San Francisco, as well as representatives for Kaiser Permanente. Together they examined more than a decade of medical records for more than 1.2 million people in Southern California age 60 or older.

The researchers found that increased exposure to particulate matter in the air from wildfire smoke raises the risk of a person over 60 being diagnosed with dementia by 18%, Casey said.

This exposure can come from longer bouts of exposure during an extended wildfire season or it can come from short but intense bursts during days with particularly bad air quality, Casey said.

Wildfire smoke isn't just smoke, it also contains harmful pollutants and particulate matter, colloquially called PM2.5 because the particles are smaller than 2.5 micrometers (about 30 times smaller than the width of a strand of hair).

Some of that particulate matter, Casey said, can be up to 25 times smaller than that. They can be so small that they can move directly from a person's nose, into their bloodstream and into their brain, hampering cognitive function and elevating the dementia risk.

Already perhaps 10% of people over 65 have dementia, Casey said. There are several types, including Alzheimer's, and these diseases aren't something for which doctors have effective treatments, so such a sharp risk increase from wildfire smoke is substantial.

That risk will increase further as climate change worsens our fire seasons. The warming atmosphere, caused by humans burning fossil fuels, will mean that wildfires will ignite more often and burn hotter. Not only does this deepen the severity of days with poor air quality but it also expands the scope of the wildfire smoke beyond the American West. Earlier this year, fires in Canada blanketed much of the eastern United States in smoke with the haze even reaching as far as New York City.

For this study, scientists examined records from 2008 to 2019, representatives for the University of Washington said in a release. So the findings don't include the summers of 2020 and 2021, some of California's most severe wildfire seasons.

Dementia isn't the only risk associated with wildfire smoke. Those with prolonged exposure could also suffer from respiratory or cardiovascular problems, especially those with preexisting heart and lung issues.

People living on the streets, working outdoors or with less access to information and medical care are also more likely to suffer from the worsening air quality, Casey said. Whenever possible they should try to limit their exposure, either by staying inside, wearing masks or using air filters.

While the latest study adds to the body of knowledge surrounding wildfire smoke, Casey said much more work is needed. The study should be repeated in other populations and across a broader geographic range.

The impacts of wildfire smoke is a growing field of research, Casey said, in part because the influence of this worsening air quality is reaching far beyond its normal boundaries.

"Wildfire smoke is no longer a one-off event," Casey said. "This is about the health of all Americans."

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