Incident dementia was tied to exposure to fine particulate matter, especially air pollution from wildfires and agriculture, an observational study of 28,000 adults over age 50 suggested.
Over 10 years, higher concentrations of total PM2.5 -- particulate matter smaller than 2.5 microns in diameter -- were associated with greater rates of incident dementia (HR 1.08 per IQR of residential PM2.5 concentrations, 95% CI 1.01-1.17), reported Boya Zhang, PhD, of the University of Michigan in Ann Arbor, and co-authors.
Associations differed across emission sources. The strongest and most robust associations were for PM2.5 from wildfires (HR 1.05, 95% CI 1.02-1.08) and agriculture (HR 1.13, 95% CI 1.01-1.27), Zhang and colleagues wrote in .
"Our data suggest that, in addition to the more obvious health impacts of wildfire smoke -- like irritation to our throats and eyes, along with breathing difficulties -- high smoke days might be taking a toll on our brains," Zhang told MedPage Today.
"While individual wildfires may be short-lived, these events are becoming more frequent in our communities due to warmer temperatures, earlier spring snowmelt, and longer fire seasons," she said. "As we've seen, wildfire smoke can also travel very far distances."
"Wildfire smoke is becoming a more widespread stressor in the United States with many cities experiencing over 30 days impacted by smoke each year," Zhang added. "Given the extremely high levels of exposure during wildfires, these events are now thought to contribute up to 25% of our fine particulate matter exposures over a year across the U.S. and 50% in some western regions."
Wildfires also release components that are likely to be highly toxic because they burn both natural and synthetic materials, Zhang and co-authors observed.
Air pollution is considered a key modifiable risk factor for dementia, according to a 2020 Lancet Commission report. Fine particulate matter may affect cognitive function through neuroinflammation due to systemic inflammation stemming from lung irritation, the researchers noted. It's also been proposed that nanoparticles of pollutants may enter the brain or cross the .
Earlier this year, the EPA sought to tighten the national annual limit on particulate matter pollution by proposing updates to the National Ambient Air Quality Standards for Fine Particulate Matter, aiming to lower the primary (health-based) annual PM2.5 standard to 9.0-10.0 µg/m3, down from its current cutoff of 12.0 µg/m3.
Zhang and colleagues conducted the Environmental Predictors of Cognitive Health and Aging (EPOCH) study using biennial survey data from 1998 through 2016 in the (HRS), a nationally representative U.S. cohort. The researchers included 27,857 people over age 50 who were dementia-free at baseline.
The researchers assessed 10-year means for total PM2.5 and PM2.5 from nine emission sources -- agriculture, road traffic, non-road traffic, coal combustion for energy production, other energy production, coal combustion for industry, other industry, wildfires, and windblown dust -- at participant residences for each month during follow-up.
The main outcome was incident dementia, classified by a validated algorithm incorporating cognitive testing and proxy respondent reports. Mean baseline age was 61 and 56.5% of the cohort were women. Most participants were white (69%), 17% were Black, and 11% were Hispanic.
Over a mean follow-up of 10.2 years, 4,105 participants (15%) developed dementia. Median 10-year total PM2.5 concentration during follow-up was 11.2 μg/m3. Among people who developed dementia, it was 12.2 μg/m3.
In single-pollutant models, PM2.5 from all sources except dust were associated with increased rates of dementia. After adjusting for PM2.5 from other sources and co-pollutants like coarse particulate matter, nitrogen dioxide, and ozone, PM2.5 from wildfires and agriculture were most strongly associated with greater rates of dementia.
A secondary analysis estimated that, if effects were causal, nearly 188,000 new cases per year of dementia in the U.S. were attributable to total PM2.5 exposure.
The findings may have been influenced by unmeasured confounding or selection bias, the researchers acknowledged.
Disclosures
This analysis was supported by the National Institutes for Environmental Health Sciences and Aging. The Health and Retirement Study was funded by the National Institute on Aging and the Social Security Administration.
Researchers reported relationships with the Health Effects Institute, Alzheimer's Association, National Institute on Aging, U.S. Environmental Protection Agency, NIH, and the National Institutes of Environmental Health Sciences.
Primary Source
JAMA Internal Medicine
Zhang B, et al "Comparison of particulate air pollution from different emission sources and incident dementia in the US" JAMA Intern Med 2023; DOI: 10.1001/jamainternmed.2023.3300.