Particulate air pollution from different emission sources, cognitive performance, and cognitive declines in India

Low- and middle-income countries experience some of the highest fine particulate matter (PM_2.5) exposures globally, with emissions from sources like residential combustion, industry, and transportation continuing to increase in many locations. While total PM_2.5 has been linked to cognitive decline, little is known about the relative importance of PM_2.5 from different emission sources, especially in low and middle-income settings.

We used cognitive performance data from the 2017-2019 and 2022-2024 waves of the Harmonized Diagnostic Assessment of Dementia for the Longitudinal Aging Study in India (LASI-DAD) and 5-year average PM_2.5 concentrations of total mass and mass from 9 emission sources estimated at each participant's residential location using spatiotemporal models. We then quantified associations of these exposures with cognitive performance and decline using generalized estimating equation models accounting for survey weights and clustering, as well as adjusted for age, gender, individual and community-level socioeconomic status, urbanicity, place-related covariates, fuel type use, and co-pollutants.

Among 5,699 participants (mean age: 70±8 years), we observed total PM_2.5 concentrations ranging from 16 to 206 μg/m³. Higher concentrations of total PM_2.5 were not associated with cognitive performance at baseline but were associated with faster declines over time (-0.012/year per SD, 95 % CI: -0.021, -0.004). Among PM_2.5 from different sources, PM_2.5 from energy production, industry, and residential combustion were associated with steeper cognitive declines over time, whereas PM_2.5 from agriculture, transportation, wildfires, and windblown dust were associated with slower cognitive declines.

Higher long-term total ambient PM_2.5 concentrations and those from residential combustion sources were associated with accelerated cognitive declines. This suggests that intervention in residential sources might reduce or delay the onset of dementia and promote healthier aging in low and middle-income settings.