Long-term exposure to the components of fine particulate matters and disability after stroke: Findings from the China National Stroke Screening Surveys

Background: Long-term exposure to ambient fine particulate matter (PM_2.5) has been linked to an increased risk of stroke. However, the effect of long-term exposure to PM_2.5 and its major components on the functional disability of stroke patients remains unclear.

Methods: Based on China National Stroke Screening Survey data obtained from 2013 to 2019, we conducted a national multicenter longitudinal study of the associations of long-term exposure to PM_2.5 and its components with the risk of disability after stroke in China. Post-stroke disability was assessed using the modified Rankin scale (mRS), which ranges from 0 to 5, with higher scores indicating greater disability. Long-term exposure to PM_2.5 and its five components [sulfate (SO₄^2-), nitrate (NO₃^-), ammonium salt (NH₄⁺), organic matter (OM), and black carbon (BC)] was determined based on average concentrations during the 3 years preceding mRS administration according to the geographic coordinates of residential communities, using state-of-the-art estimates from multiple sources. We used a fixed-effect model to evaluate the associations between mRS scores and PM_2.5 exposure, with adjustment for multiple covariates.

Results: Every 10 µg/m³ increase in PM_2.5 was associated with a 0.019 (95% confidence interval, 0.003, 0.036) increase in mRS score, but the effect was not significant after adjusting for all covariates [0.016 (95% CI, -0.003, 0.032)]. For PM_2.5 components, each IQR (7.92 µg/m³) increment in OM exposure was associated significantly with 0.062 (95% CI, 0.013, 0.111) increment in the mRS score. A significant association was observed between SO₄^2- exposure and the mRS score [0.057 (95% CI, 0.003, 0.112), per IQR: 6.28 µg/m³]. However, no significant association was found with BC, NO₃^-, or NH₄⁺ exposure. Furthermore, the nonlinear curves were observed for the exposure-response relationship between PM_2.5 exposure and the mRS score.

Conclusion: Greater PM_2.5 exposure increased the mRS score and was associated with post-stroke functional disability among stroke patients. However, different chemical components showed unequal neurotoxic effects, and long-term exposure to OM and SO₄^2- may play a more important role.

Synopsis: This study reports fine particulate matter at higher concentrations damages the functional ability among specific stroke patients, and PM_2.5 components have different neurotoxicities.