Association Between Ambient Temperature And Ischemic Stroke Mortality And The Effect Modifications By Greenness

ObjectiveTo explore the impact of ambient temperature on ischemic stroke mortality and identify vulnerable populations.To further evalute the potential modifying effects of greenness on this impact to inform effective responses to climate change and reduce stroke burden.MethodsWe collected data on daily average temperature,ischemic stroke deaths and greenness in 19 counties of Shandong Province from 2013 to 2019.First,we applied quasi-Poisson regression combined with a distributional lagged nonlinear model（DLNM）to estimate the county-specific association between temperature and ischemic stroke mortality.Second,we used a random-effects multivariate meta-analysis joint best linear unbiased prediction（BLUP）to combine county-specific effects;and further calculated cumulative relative risks（CRRs）and attributable fractions（AFs）for selected temperatures using the minimum mortality temperature（MMT）as the threshold temperature;and identified gender,age,and regional variability by Z-test.Finally,we adopted a multivariate meta-regression to quantitatively estimate the effect modifications of greenness on the risk of ischemic stroke mortality associated with extreme temperatures,using normalized difference vegetation index（NDVI）,soil-adjusted index（SAVI）and enhanced vegetation index（EVI）as vegetation measures.Results（1）A total of 86,873 ischemic stroke deaths were reported from 2013 to 2019,with a 7-year average temperature of 14.3°C,an average relative humidity of 64.1%,average summer vegetation cover at a moderate level（e.g.,NDVI of 0.47）,and high average air pollutant concentrations,especially PM_2.5（70.3μg/m³）and O₃（105.0μg/m³）exceeding the national level concentration limits.（2）At the county level,the relationships between temperature and ischemic stroke mortality were approximately inverted"J",but there was moderate heterogeneity between the effects(I²_{（lag 14d）}=26.8%,P<0.01).In estimating CRRs for extreme temperature,we observed that both extreme cold（2.5th）and extreme heat（97.5th）significantly increased the risk of ischemic stroke mortality in some counties,with the former showing the greatest effect in Wendeng[CRR=2.43,95%Confidence Interval（CI）:1.47 to 4.03],and the latter having the strongest hazard in Bincheng（CRR=3.10,95%CI:2.00-4.80）.Further in estimating AFs for specific temperatures,we found that moderate low cold（2.5th to MMT）caused the majority of attributable mortality burdens in most counties,while moderate heat（MMT to 97.5th）contributed to higher attributable burden with increasing latitude,both of which showed the highest attributable proportions in Wendeng,19.79%and 4.28%,respectively.（3）At the pooled level,we found that the overall exposure-response relationship between temperature and ischemic stroke mortality at different lags still showed an inverted"J"distribution,but the lag duration of cold was significantly longer than that of heat.In terms of CRRs,both extreme cold and extreme heat significantly increased the risks of mortality from ischemic stroke,with the former（CRR=1.66,95%CI:1.24-2.23）being higher than the latter（CRR=1.54,95%CI:1.32-1.80）;in terms of AFs,non-optimum temperatures（≠MMT）could cause 20.05%of the attributable mortality burden,with cold（<MMT）and heat（>MMT）causing 17.09%and 2.96%,respectively,with a particular predominance of moderate cold（16.28%）.（4）After stratified analysis,we observed that the mortality burden attributable to moderate cold was higher in males and those aged 0-64 years,with the value of18.94%and 15.76%,respectively,whereas the mortality burden attributable to moderate heat was greater in females and those aged≥65 years,with the value of1.85%and 1.74%,respectively.Moreover,the north was most vulnerable to heat compared to other regions,with an AF of 5.59%.（5）Each 0.1 unit increase in summer NDVI,SAVI and EVI was associated with some decreased CRR in relation to extreme heat,especially significant in males and those≥65 years.ConclusionsBoth cold and heat increased the burdens of ischemic stroke mortality,and cold—moderate cold,explained most of the attributable buredens.Males and those aged 0-64 years were more susceptible to moderate cold,whereas females and those aged≥65 years were more vulnerable to heat.And the risk of heat,especially extreme heat,is intensifying with increasing latitude.However,A higher greenness level could significantly alleviate the effects of extreme heat on ischemic stroke mortality.