Long-term Exposure to Air Pollution May Lead to Dementia

By Rob Dillard - Last Updated: August 15, 2023

Individuals who are exposed to higher levels of air pollution over a long-term duration, particularly pollution from agriculture and wildfires, have a greater risk of dementia, according to a new study published in JAMA Internal Medicine.

Exposure to fine particulate matter (PM2.5) air pollution was recently recognized as a risk factor for dementia, as it affects cognition by causing brain inflammation related to the systemic inflammation and stressed oxygen levels following lung irritation. “PM2.5 originates from many sources in the environment, including traffic, coal-fired power plants, agricultural emissions, and wildfires. Each source can emit PM2.5 with distinct physical and chemical characteristics,” the investigators wrote. As PM2.5 is typically measured by total mass, it remains unclear how air pollution from different emission sources affects the brain. This analysis sought to assess the correlation between incidence of dementia and long-term PM2.5  from 9 unique emission sources in older adults.

The investigators utilized biennial survey data from January 1998 to December 2016 for participants in the nationally representative, population-based Health and Retirement Study. Patients in the population of interest were all 50 years of age or older and did not have dementia at baseline. Exposure, outcome, and demographic data were available for all patients over the study period.

The study comprised 27,857 participants (mean age, 61 years; 56.5% female) who were assessed based on the 10-year average total PM2.5 and PM2.5 from 9 emission sources—agriculture, road traffic, nonroad traffic, coal combustion for energy production, other energy production, coal combustion for industry, other industry, wildfires, and windblown dust—at their residences using spatiotemporal and chemical transport models. The primary end point of interest was defined as incident dementia.

The results showed that higher concentrations of total PM2.5 were linked to greater rates of incident dementia (hazard ratio, 1.08 per interquartile range; 95% CI, 1.01-1.17). Overall, the researchers observed that PM2.5 from all sources except windblown dust was associated with increased rates of dementia. The strongest associations were found in exposure to agriculture, road traffic, coal combustion, and wildfires.

“These findings support the hypothesis that airborne particulate matter pollution is associated with the likelihood of developing dementia and suggest that selective interventions to reduce pollution exposure may decrease the life-long risk of dementia; however, more research is needed to confirm these relationships,” the researchers concluded.

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