Wildfire exposure spell dementia risk

Exposure to fine particulate matter (PM_2.5) from wildfire smoke carries a heightened risk of dementia, as shown in a study.

In adjusted pooled logistic regression models, every 1-μg/m³ increase in the 3-year mean of wildfire PM_2.5 exposure was associated with an 18-percent increase in the odds of dementia diagnosis (odds ratio [OR], 1.18, 95 percent confidence interval [CI], 1.03–1.34). This association was especially pronounced among KPSC members who were not more than 75 years of age at baseline, those from racially minoritized subgroups, and those residing in high-poverty vs low-poverty areas. [JAMA Neurol 2024;doi:10.1001/jamaneurol.2024.4058]

On the other hand, a 1-μg/m³ increase in nonwildfire PM_2.5 exposure was associated with a 1-percent increase (OR, 1.01, 95 percent CI, 1.01–1.02).

“One microgram per metre cubed might sound fairly small, but we have to think about how people are exposed to wildfire smoke. Most days they aren’t exposed at all, so this might represent a few days of exposure at a concentration of something like 300 µg/m³, where the Air Quality Index is over 200 in someone's community,” according to lead study author Prof Joan Casey from the University of Washington School of Public Health in Seattle, Washington, US.

“When you think about it, it’s actually a few really severe wildfire smoke days that might translate into increased risk,” Casey said.

Wildfire PM_2.5 concentrations tend to fluctuate intermittently, characterized by periods of elevated levels, while exposure to nonwildfire PM_2.5 is generally more stable throughout the year, Casey explained. Additionally, wildfire PM_2.5 has a smaller particle size, contains higher concentrations of harmful compounds, and is generated by higher-temperature combustion of organic materials, she added. [Epidemiology 2022;33:167-175; Sci Total Environ 2010;408:644-651; Med J Aust 2020;212:349-353.e1; Proc Natl Acad Sci USA 2024;121:e2306729121]

Meanwhile, the differential health risks from wildfire PM_2.5 exposure within subpopulations align with prior research indicating that individual-level and area-level social determinants compound the risk of adverse health outcomes associated with climate-driven environmental exposures, the author noted. [N Engl J Med 2023;388:943-949; Curr Environ Health Rep 2022;9:80-89]

Casey called for additional research to examine the effects of air pollution on potentially vulnerable population subgroups with the aim to identify potential strategies to mitigate inequities in air pollution exposure effects.

“The main culprit here is climate change. It’s a global problem,” she said. “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.”

The analysis included 1,223,107 members (median age 62 years, 53.0 percent female, 49.0 percent non-Hispanic White) of Kaiser Permanente Southern California (KPSC) who were at least 60 years of age. Three-year rolling mean wildfire and nonwildfire PM_2.5 exposure was estimated using monitoring and remote-sensing data and statistical techniques. The primary outcome of incident dementia was determined using diagnostic codes in the electronic health records.

During the 3-year observation period, the median rolling average for wildfire PM_2.5 concentration was 0.09 μg/m³, while the median nonwildfire PM_2.5 concentration was 11.2 μg/m³. Dementia was diagnosed in 80,993 KPSC members (6.6 percent).