Long-Term Wildfire Smoke Exposure Linked to Dementia Risk, Study Finds

Among nine sources of particle pollution, fires and agriculture had the strongest link to dementia, according to a new analysis of a national survey

An aerial view of smoke rising from buildings burning from wildfires.
Smoke rises from buildings destroyed in the town of Lahaina last week by the Maui wildfires. A new study ties long-term exposure to smoke from wildfires to increased risk of dementia. Justin Sullivan / Getty Images

A new study suggests that long-term exposure to wildfire smoke can negatively impact the brain years down the road.

The research, published Monday in the journal JAMA Internal Medicine, finds that people who lived in areas with high levels of particulate air pollution were more likely to develop dementia. Among nine different sources of this pollution, the scientists found that wildfires and agriculture had the strongest link to cognitive decline.

“Our data suggest that, in addition to the more obvious health impacts of wildfire smoke—like irritation to our throats and eyes, along with breathing difficulties—high smoke days might be taking a toll on our brains,” Boya Zhang, first author of the paper and an environmental epidemiologist at the University of Michigan, tells MedPage Today’s Judy George.

“It’s a great study, a great population, and it’s got terrific data,” Marc Weisskopf, an environmental epidemiologist at Harvard University who was not involved in the research, tells Stat News’ Abdullahi Tsanni. “They’re going the next step to parse out what are the different components of air pollution that matter more than others.”

In particular, the study looks at fine, inhalable particles known as PM2.5, which are at least 30 times smaller in diameter than the width of a human hair, according to the Environmental Protection Agency (EPA). PM2.5 enters the air from various sources, such as construction sites, smokestacks and wildfires. It can also form in the atmosphere from reactions between chemicals emitted by power plants and automobiles.

PM2.5 exposure has already been linked to a litany of health problems in humans, including heart attacks, asthma, decreased lung function and premature death in people with heart or lung disease, per the EPA. It’s also been linked to lung cancer and mortality from various cancers as well. Several other studies have tied air pollution to dementia, writes CNN’s Jen Christensen.

But the health effects of wildfire smoke are especially relevant now. The study comes just one week after devastating fires ignited in Maui, killing 101 people and destroying the historic town of Lahaina. Wildfires have polluted the air across a wide stretch of the world this summer, including California, Greece and Canada. In some cases, the pollution has spread far beyond where the fires burned—smoke from Canada’s fires blanketed the eastern United States and even reached Norway.

“Wildfire smoke is becoming a more widespread stressor in the United States, with many cities experiencing over 30 days impacted by smoke each year,” Zhang tells MedPage Today. “Given the extremely high levels of exposure during wildfires, these events are now thought to contribute up to 25 percent of our fine particulate matter exposures over a year across the U.S. and 50 percent in some western regions.”

The new study examined data collected from 1998 to 2016 during a nationally representative survey that tracked PM2.5 exposure. The researchers specifically looked at 27,857 people over the age of 50 who did not have dementia to begin with.

However, around 15 percent of these participants developed dementia over the course of the survey, and this was linked with higher levels of PM2.5 exposure, especially when the source was wildfires or agriculture.

Perhaps this has to do with the content of the pollution from these sources, senior author Sara Dubowsky Adar, an epidemiologist at the University of Michigan, tells CNN. Agriculture uses pesticides, which are neurotoxins and therefore might affect the brain. And wildfires moving through developed areas burn vehicles, plastics, painted surfaces and hazardous waste, which creates toxic particles that can be inhaled.

Still, scientists aren’t sure of the exact mechanism though which PM2.5 can change the brain.

“Is that causing the cardiovascular failure that leads to the less oxygen supply to the brain, and then that caused the accelerating dementia, or the PM is getting into the brain and causing some neurotoxic reaction? We still don’t know yet,” Masashi Kitazawa, an environmental and occupational health researcher at the University of California, Irvine, who was not involved in the study, tells CNN.

The results suggest that reducing people’s exposure to air pollution from sources like wildfires could decrease their risk of developing dementia, but further research is needed to know for sure, according to the study authors.

In the meantime, though, they urge caution. “If there are ways to keep people away from the smoke when it happens, then that would lessen the impact on dementia,” Weisskopf tells Stat News.

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