Short-term exposure to nitrogen dioxide and emergency department visits for cause-stroke: a time-series study in Shanghai, China, 2013–2022

Abstract

Background: The association between air pollution and an increased risk of cardiovascular diseases, including stroke, is well-established. However, it remains unclear how reductions in pollutant levels—resulting from clean air policies and the COVID-19 lockdown—affect this relationship.

Methods: A time-series study was conducted using data from Shanghai, China, spanning from 2013 to 2022, divided into two periods (2013–2019 and 2020–2022). Daily air pollution data were obtained from China’s air quality platform, while stroke emergency department (ED) visits were sourced from Renhe Hospital. We employed quasi-Poisson regression to analyze the relationship between daily pollutant levels and stroke ED visits, with stratified analyses by sex, age, season, and period. The study identified significant reductions in six pollutants (PM_2.5, PM_10–2.5, PM₁₀, SO₂, NO₂, CO) during the 2020–2022 period compared to 2013–2019.

Results: Significant reductions in six air pollutants (NO₂, PM_2.5, PM_10–2.5, PM₁₀, SO₂, CO) were observed during 2020–2022 compared to 2013–2019. Higher daily NO₂ levels were associated with an increased risk of stroke and its subtypes throughout the study, with a stronger correlation observed in the 2020–2022 period (P < 0.001). Subgroup analyses indicated that females and individuals aged 65–74 experienced the highest risks. The elevated stroke risk was particularly pronounced in the summer during 2020–2022. A two-factor model demonstrated that combined exposure to NO₂ and other pollutants increased stroke risk.

Conclusions: This study heightened that reduced NO₂ levels generally mitigate the adverse effects of short-term exposure to air pollutants on stroke risk, although the benefits vary among subgroups. The persistent stroke risk despite lower pollutant levels underscores the complex factors influencing stroke risk, highlighting the need for comprehensive intervention strategies.