UW-led research links wildfire smoke with increased dementia risk

New research from the University of Washington highlights the dangers of wildfire smoke as related to dementia.

Studies have linked exposure to fine particulate matter contained in smoke, known as PM2.5, with an increased risk of developing dementia. Researchers believe that some sources of PM2.5 may be more hazardous than others.

As the Baby Boomer generation enters retirement, approximately one in six Americans is now over the age of 65. While the number of Americans living with dementia is expected to rise, the proportion of older adults developing dementia has actually decreased. The reasons for this decline are not entirely clear, but various lifestyle and environmental factors can influence the risk of cognitive decline.

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An analysis of health care records from 1.2 million Southern California residents revealed that long-term exposure to wildfire smoke significantly increased the likelihood of a dementia diagnosis.

The findings were presented at the Alzheimer’s Association International Conference in July and published in JAMA Neurology on Nov. 25.

“There have been studies linking total PM2.5 to dementia, but none specifically focused on wildfire PM2.5,” said lead author Joan Casey, an associate professor at UW’s Department of Environmental & Occupational Health Sciences. “Wildfire smoke is unique because it can be extremely intense on certain days.”

Researchers examined the health records of Kaiser Permanente Southern California members aged 60 and older from 2008 to 2019, all initially free of dementia. They estimated each person’s long-term exposure to both wildfire and non-wildfire PM2.5 over a three-year rolling average and identified those diagnosed with dementia.

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The study found that for every 1 microgram per cubic meter (µg/m3) increase in three-year average wildfire PM2.5 concentration, the odds of a dementia diagnosis rose by 18%. Non-wildfire PM2.5 also increased dementia risk, but to a lesser extent.

“One microgram per cubic meter might seem small, but considering how people are exposed to wildfire smoke, it represents a few days of very high exposure,” Casey explained. “These severe smoke days can significantly increase risk.”

The risk was even higher among minorities and those living in high-poverty areas, reflecting long-term trends where vulnerable populations face greater environmental hazards. The disparities may be due to lower-quality housing, which allows more smoke to enter, or the inability to afford air filtration systems.

The study did not include the extreme wildfire seasons of 2020 and 2021 in California. The climate crisis has increased the frequency and severity of wildfires in the American West, leading to a “smoke season” that has eroded air quality improvements made over the past century.

“The main culprit is climate change,” Casey said. “While individuals can protect themselves with air filters and masks, we need a global solution to climate change. It’s a complex problem that requires a multifaceted approach.”

Bill Kaczaraba is a content editor at MyNorthwest. You can read his stories here. Follow Bill on X, formerly known as Twitter, here and email him here.