The association between PM_2.5 components and cognitive decline: the impact of measurement error correction

Growing evidence suggests that exposure to fine particulate matter (PM_2.5) may accelerate cognitive decline and increase dementia risk, but the roles of individual PM_2.5 components, particularly when accounting for exposure measurement error, remain unclear. We followed 12,824 participants in the Nurses' Health Study cognition substudy (2000-2008). One-year average PM_2.5 component concentrations preceding each participant's first cognitive assessment were assigned based on residential address. A global cognitive score was calculated as the mean of z-scores from six tests, and individual rates of cognitive decline were estimated using linear mixed models with random intercepts and slopes. Using information on the relationships of personal exposures and nearest-monitor PM_2.5 components from a prior validation study, we employed double/debiased machine learning (DML) method to estimate associations between PM_2.5 components and cognitive decline while accommodating high-dimensional multi-pollutant exposures and accounting for exposure measurement error. Higher exposure to several PM_2.5 components were associated with changes in rates of cognitive decline. In multi-pollutant models without measurement error correction, each doubling of chloride (Cl) concentration was associated with a 0.0003 (95% CI: 0.0000, 0.0005) standard unit slower annual rate of cognitive decline, while each doubling in silicon (Si) was associated with a -0.0025 (95% CI: -0.0050, 0.0000) faster rate of decline. After correction for measurement error, associations generally strengthened: higher bromine (Br), manganese (Mn), and lead (Pb) were significantly associated with faster cognitive decline. In contrast, higher strontium (Sr) and vanadium (V) were associated with slower decline. Our findings suggest that long-term exposure to certain PM_2.5 components, and their sources, may be more detrimental to cognitive aging than others, and highlight the critical need to correct for measurement error when assessing the health impacts of PM_2.5 and its components. More research is needed to confirm these findings, ideally with access to larger validation studies of component exposures.