Exposure-Response to High PM2.5 Levels for Cardiovascular Events in High-risk Older Adults in Taiwan

BackgroundMultiple studies from countries with relatively lower PM2.5 level demonstrated that acute and chronic exposure even at lower than recommended level, e.g., 9 g/m3 in the US increased the risk of cardiovascular (CV) events. However, limited studies using individual level data exist from countries with a wider range of PM levels to illustrate shape of the exposure-response curve throughout the range including > 20 g/m3 PM2{middle dot}5 concentrations. Taiwan with its policies reduced PM2.5 over time provide opportunities to illustrate the dose response curves and how reductions of PM2.5 over time correlated with CV events incidence in a nationwide sample. MethodsUsing data from the 2009-2019 Taiwan National Health Insurance Database linked to nationwide PM2.5 data. We examined the shape and magnitude of the exposure-response curve between seasonal average PM2{middle dot}5 level and CV events-related hospitalizations among older adults at high-risk for CV events. We used history-adjusted marginal structural models including potential confounding by individual demographic factors, baseline comorbidities, and health service measures. To quantify the risk below and above 20 g/m3 we conducted stratified Cox regression. We also plotted PM2.5 and CV events from 2009-2019 as well as average temperature as a comparison. FindingsUsing the PM2.5 concentration <15 g/m3 (Taiwan regulatory standard) as a reference, the seasonal average PM2.5 concentration (15-23.5g/m3 and > 23.5 g/m3) were associated with hazard ration of 1.13 (95%CI 1.09-1.18) and 1.19 (95%CI 1.14-1.24), 1.07 (95%CI 1.03-1.11) and 1.14 (95%CI 1.10-1.18), 1.22 (95%CI 1.08-1.38) and 1.31 (95%CI 1.16-1.48), 1.04 (95%CI 0.98-1.10) and 1.10 (95%CI 1.04-1.16) respectively for HF, IS/TIA,PE/DVT and MI/ACS. A nonlinear relationship between PM2{middle dot}5 and CV events outcomes was observed at PM2{middle dot}5 levels above 20 g/m3. InterpretationA nonlinear exposure-response relationship between PM2{middle dot}5 concentration and the incidence of cardiovascular events exists when PM2.5 is higher than the levels recommended by WHO Air Quality Guidelines. Further lowering PM2{middle dot}5 levels beyond current regulatory standards may effectively reduce the incidence of cardiovascular events, particularly HF and DVT, and can lead to tangible health benefits in high-risk elderly population.