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.

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

Methods: We collected data on daily IS deaths, daily PM 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 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 and green space on IS mortality.

Results: A total of 10 799 IS deaths were included in our study. Exposure to PM 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 on lag0 and 1.0317 (95% CI = 1.0016, 1.0627) on lag01. The links between PM and IS mortality were not significantly different across genders, ages, or PM zones. Furthermore, our results showed that the effects of PM on IS mortality were higher in low levels of green space. Specifically, for each IQR increase in PM, 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 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 was significantly associated with increasing odds of IS mortality. Furthermore, there were synergetic impacts between PM 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 levels, can help prevent premature deaths from IS.