Study finds wildfire smoke exposure increases dementia risk

It’s well known that wildfire smoke can hurt the lungs and heart. But now, a California study of 1.2 million people links the hazy pollutant to brain harm and, specifically, higher dementia risk.

The decadelong study suggests that the brain threat caused by wildfire smoke is higher than from other air pollutants, such as by vehicles and factories. The findings were released Monday at the Alzheimer’s Association conference in Philadelphia.

Fine particulate matter is a microscopic mixture of solid and liquid droplets in the air 30 times smaller than the width of an average human hair. Researchers found that the risk of dementia diagnosis from exposure to particulate matter in wildfire smoke was notably stronger – even with less exposure – than the risks from those other sources of air pollution.

Smoke from regional wildfires has lingered the past few days in Spokane. The concern rises from what is in that wildfire smoke – a mix of fine particles and gases from burning trees, buildings and other materials that can reach areas far from a fire’s source.

If regional air quality worsens, people – especially children and patients with chronic conditions – are advised to stay indoors or wear an N95 mask.

The study’s researchers also urge people to update their indoor air filtration systems and check the outdoor air quality on a weather app. An Air Quality Index number of 100 or higher means that the air is unhealthy to breathe.

Nick Hart, a Seattle-based Alzheimer’s Association public policy manager, travels across Washington state to do presentations for audiences about the latest in Alzheimer’s research. He isn’t a medical researcher or involved with this study, but Hart said it has important findings.

“It’s a significant study, because wildfires are increasingly common in the Western United States and are occurring in California, Oregon and Washington,” he said. “More and more people are affected by these wildfires, so there is an interest in how that impacts brain health.

“We’ve known that exposure to air pollution is hazardous to brain health, but wildfire smoke is produced at higher temperatures. On average, wildfire smoke has smaller fine particulates than these other types of pollutant and a greater concentration of toxic chemicals. The concern is any time you breathe it, it has direct access to the bloodstream through your respiratory system and can affect your brain.”

High levels of such particulate matter previously have been shown to raise the risk of heart disease, asthma and low birth weight.

“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.”

Researchers analyzed the health records of 1.2 million socioeconomically diverse Kaiser Permanente Southern California members who were 60 years or older between 2009 and 2019. None of the patients had been diagnosed with dementia at the research’s start. Total particulate matter was estimated from various sources, including satellite-derived aerosol properties and Environmental Protection Agency monitoring.

The researchers used air quality monitoring data, satellite imagery and machine learning techniques to separate wildfire and non-wildfire particulate. They determined each person’s exposure to both sources, and based on where they lived. They compared that information to subsequent diagnoses of dementia.

The study group observed a 21% increase in the odds of dementia diagnosis for every increase of 1 microgram per meter – an amount of particulate matter in a cubic meter of air – in the three-year average wildfire exposure. In measuring the same way for other pollutant types at similar exposure, people in the study from those only had a 3% increased risk of dementia diagnosis.

“It’s apparent the risk from exposure due to wildfire smoke is an even bigger concern,” Dr. Holly Elser, the study’s first author, said in a news release.

Elser said there are several reasons why particulates produced by wildfires might be more hazardous to health, including that they are produced at those higher temperatures, contain a greater concentration of toxic chemicals and, on average, are smaller in diameter. She said more research needs to be done.

“The findings appeared most pronounced among racial and ethnic minorities and in high-poverty areas,” added Joan A. Casey, senior author of the study and a University of Washington assistant professor in the department of environmental and occupational health sciences.

Alzheimer’s disease is the most common type of dementia, says the Centers for Disease Control and Prevention.

Nearly 7 million Americans have Alzheimer’s, the association said. About 127,000 people aged 65 and older in Washington state live with an Alzheimer’s diagnosis, based on 2020 data.

The CDC says wildfire smoke exposure also can cause asthma attacks, breathing trouble, stinging eyes, chest pains and a fast heartbeat.