Wildfire smoke hard on brain health, increases dementia risk

Wildfire smoke poses a greater risk to brain health than any other type of air pollution, according to findings of a decadeslong study released Monday at the Alzheimer’s Association International Conference in Philadelphia.

The issue is fine particulate matter pollution, designated as PM2.5, which is known to be associated with numerous health risks, including asthma, heart disease and low birth weight, among others.

To call it “fine” is an understatement: PM2.5 air pollution contains solid and liquid droplets 30 times smaller than the width of most human hair.

And in a study that lasted more than a decade and included more than 1.2 million people in Southern California, where wildfires are common, researchers found the risk of dementia diagnosis related to PM2.5 exposure in wildfire smoke is “notably stronger — even with less exposure — than the risk due to the other sources of PM2.5 air pollution,” including factories and motor vehicle emissions, according to a news release from the Alzheimer’s Association.

The research team included the University of Washington in Seattle and the Hospital of the University of Pennsylvania, Philadelphia.

“With the rising global incidence of wildfires, including in California and the western U.S., exposure to this type of air pollution is an increasing threat to brain health,” said Claire Sexton, Alzheimer’s Association senior director of scientific programs and outreach. “These findings underscore the importance of enacting policies to prevent wildfires and investigating better methods to address them.”

Alzheimer’s toll

Nearly 7 million people in the United States have dementia; Alzheimer’s disease is the most common form. And the association said that studies suggest as many as 22% of those 65 and older have mild cognitive impairment, which can precede Alzheimer’s disease. About a third of all adults 65 and older have that or another form of dementia.

Alzheimer’s is the No. 7 cause of death in the U.S., killing more people than breast cancer and prostate cancer combined. It is also, per the association, “the only leading cause of death without a prevention or cure,” though some drugs have been developed that appear to slow decline slightly.

The organization reports that about 20% of Medicare funds are spent on people with Alzheimer’s or another form of dementia. By 2050, the projection is a third of Medicare spending will be on people with dementing diseases.

Caregivers in 2021 spent an average of $12,388 out of pocket on providing care for someone with Alzheimer’s or another form of dementia. In 2022, caregivers provided 18 billion hours of unpaid care, at a value of $339.5 billion.

Health records document mental decline

The wildfire smoke study findings were based on the health records of a “socioeconomically diverse” group of Kaiser Permanente members in Southern California ages 60 or older between 2009 and 2019, the release said. None of them had been diagnosed with dementia when the study began.

To determine exposure to PM2.5, the researchers examined data from Environmental Protection Agency monitoring, as well as satellite-derived properties, other air quality monitoring data, satellite imagery and machine learning techniques to sort out what was wildfire particulate pollution and what came from other sources, based on where the study subjects lived.

Then they looked at who was later diagnosed with dementia.

The study showed a 21% increase in the odds of a dementia diagnosis for every increase of 1 microgram of particulate matter in a cubic meter of air in the three-year average wildfire PM2.5 exposure. The increased risk was much smaller from other particulate matter pollution.

“Previous research has found that exposure to PM 2.5 is associated with dementia, but in light of our large, long-term study, it’s apparent the risk from exposure due to wildfire smoke is an even bigger concern,” said Dr. Holly Elser, the study’s first author and a neurology resident at the Hospital of the University of Pennsylvania, Philadelphia. “Air pollution produced by wildfires now accounts for more than 70% of total PM 2.5 exposure on poor air quality days in California. This is a real problem.”

In the release, she said it’s possible wildfires are more risky because toxic chemicals are more concentrated in the smoke and because the particulate matter in smoke is even smaller than that from other sources. But more research is needed to determine exactly why the risk is higher.

The risk is higher in areas with a lot of poverty, the researchers found.

Both researchers recommend that people update the air filtration systems in their homes and watch the outdoor air quality index. A number higher than 100 indicates unhealthy air, indicating folks should stay inside when possible and wear an N95 mask if they have to venture outside.