Associations between short-term exposure to fine particulate matter with ischemic stroke mortality and the role of green space: a time-series study in Zibo, China.

Abstract

Background: Previous studies on associations between short-term exposure to fine particulate matter (PM_2.5) and ischemic stroke (IS) mortality reported inconclusive results. Additionally, whether and how PM_2.5 and green space interact to precipitate IS deaths remains unclear. We aimed to examine the impacts of short-term exposure to PM_2.5 on IS mortality and the role of green space in the association.

Methods: We collected data on daily IS deaths, daily PM_2.5 concentrations, and monthly normalized difference vegetation index (NDVI) in Zibo City from 2015 to 2019. Generalised additive models were adopted to investigate the short-term impacts of PM_2.5 on IS mortality, and subgroup analyses were used to examine effect modification by population characteristics. Stratified analyses by green space levels and joint effect model were conducted to test the interactions of PM_2.5 and green space on IS mortality.

Results: A total of 10 799 IS deaths were included in our study. Exposure to PM_2.5 was associated with an increased risk of IS mortality, with odds ratios (ORs) of 1.0263 (95% confidence interval (CI) = 1.0017, 1.0516) for each interquartile range (IQR) increase in PM_2.5 on lag0 and 1.0317 (95% CI = 1.0016, 1.0627) on lag01. The links between PM_2.5 and IS mortality were not significantly different across genders, ages, or PM_2.5 zones. Furthermore, our results showed that the effects of PM_2.5 on IS mortality were higher in low levels of green space. Specifically, for each IQR increase in PM_2.5, the ORs (95% CIs) of IS death in the low level and the high level of NDVI were 1.0287 (95% CI = 1.0019, 1.0563) and 0.9934 (95% CI = 0.9296, 1.0615), respectively. In addition, PM_2.5 and NDVI exhibited significant interactive effects on IS mortality, with relative excess odds due to interaction (REOI) of greater than 0.

Conclusions: Our findings showed that PM_2.5 was significantly associated with increasing odds of IS mortality. Furthermore, there were synergetic impacts between PM_2.5 and lack of greenness on IS mortality. Our results suggest that expanding green spaces, such as increasing park coverage and street greening, along with regulating industrial emissions to reduce PM_2.5 levels, can help prevent premature deaths from IS.