Effect of neighbourhood greenness on the association between air pollution and risk of stroke first onset: A case-crossover study in shandong province, China

Background: Higher neighbourhood greenness is associated with beneficial health outcomes, and short-term exposure to air pollution is associated with an elevated risk of stroke onset. However, little is known about their interactions. Methods: Daily data on stroke first onset were collected from 20 counties in Shangdong Province, China, from 2013 to 2019. The enhanced vegetation index (EVI) and concentrations of fine particulate matter (PM2.5), nitrogen dioxide (NO2), ozone (O-3), carbon monoxide (CO), and sulfur dioxide (SO2) were calculated for each individual at the village or community level based on their home address to measure their neighbourhood exposure to greenness and air pollution. EVI was categorised as low or high, and a time-stratified case-crossover design was used to estimate the percent excess risk (ER%) of stroke associated with short-term exposure to air pollution. We further stratified greenness on the basis of EVI values into quartiles and introduced interaction terms between air pollutant concentrations and the median EVI values of the quartiles to assess the effect of greenness on the associations between short-term exposure and stroke. Results: Individuals living in the high-greenness areas had weaker associations between total stroke risk and exposure to NO2 (low greenness: ER% = 1.765% [95% CI 1.205%-2.328%]; high greenness: ER% = 0.368% [95% CI-0.252% to 0.991%]; P = 0.001), O3 (low greenness: 0.476% [95% CI 0.246%-0.706%]; high greenness: ER% = 0.085% [95% CI-0.156% to 0.327%]; P = 0.011), and SO2 (low greenness: 0.632% [95% CI 0.138%-1.129%]; high greenness: ER% =-0.177% [95% CI-0.782% to 0.431%]; P = 0.035). Conclusion: Residence in areas with higher greenness was related to weaker associations between air pollution and stroke risk, suggesting that effectively planning green spaces can improve public health.