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Wildfire smoke exposure and dementia risk

The study suggests that fine particulate pollution from wildfires may significantly raise the risk of dementia. Dave Mills / Stocksy / Adobe Stock

Long-term exposure to fine particulate matter less than 2.5 microns in diameter (PM_2.5), a type of air pollution, has been linked to an increased risk of dementia. In the Western United States, wildfires are becoming a common source of airborne PM_2.5. But it isn’t clear whether the fine particles from wildfires confer a similar dementia risk to those from other sources.

An NIH-funded research team, led by Dr. Joan Casey of the University of Washington School of Public Health, compared the links between exposure to PM_2.5 from wildfire or other sources and new cases of dementia. To do so, they looked at electronic health records of more than 1.2 million Kaiser Permanente Southern California members aged 60 or older who were initially free from dementia. The health data spanned the years 2008-2019. The researchers estimated total PM_2.5 concentrations by census tract (a small, defined area) from 2006-2019 using air quality and weather data. They also used data on wildfires to separate wildfire PM_2.5 from other sources of PM_2.5. Results appeared in JAMA Neurology on November 25, 2024.

More than 80,000 people in the study received a dementia diagnosis. The team looked at how dementia diagnoses varied with average PM_2.5 concentrations over the previous three years. They found that for every 1 μg/m³ increase in average wildfire PM_2.5, the odds of receiving a dementia diagnosis increased by 18%. In contrast, a 1 μg/m³ increase in average PM_2.5 from other sources was associated with only a 1% increase in the odds of a dementia diagnosis.

The researchers next looked at how these associations varied with age, sex, race/ethnicity, and neighborhood poverty. The association between wildfire PM_2.5 and dementia incidence was stronger among people who were less than 75 years old at baseline compared to those who were 75 and older. People who lived in poorer areas also showed a stronger association between wildfire PM_2.5 and dementia. And the association was stronger among certain minority groups, such as Asian and non-Hispanic Black people.

The findings suggest that PM_2.5 from wildfires is a greater risk factor for dementia than PM_2.5 from other sources. This risk may be particularly pronounced among socially and economically disadvantaged groups. Interventions that reduce wildfire PM_2.5 exposure could potentially reduce dementia incidence. They might also reduce socioeconomic disparities in dementia incidence.

As the earth’s climate changes, wildfires are becoming a bigger problem. “It’s a global problem,” Casey says. “While individuals can protect themselves with air filters and masks, we need a global solution to climate change. It’s going to have to be many-pronged—many people have to be involved to solve this highly complex problem.” 

—by Brian Doctrow, Ph.D.