Exposure-Response to High PM _2.5 Levels for Cardiovascular Events in High-risk Older Adults in Taiwan

Multiple studies from countries with relatively lower PM _2.5 level demonstrated that acute and chronic exposure even at lower than recommended level, e.g., 9 μg/m ³ 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 μg/m ³ PM _2·5 concentrations. Taiwan with its policies reduced PM _2.5 over time provide opportunities to illustrate the dose response curves and how reductions of PM _2.5 over time correlated with CV events incidence in a nationwide sample.

Using 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 PM _2·5 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 μg/m ³ we conducted stratified Cox regression. We also plotted PM _2.5 and CV events from 2009-2019 as well as average temperature as a comparison.

Using the PM _2.5 concentration <15 μg/m ³ (Taiwan regulatory standard) as a reference, the seasonal average PM _2.5 concentration (15-23.5μg/m ³ and > 23.5 μg/m ³ ) 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 PM _2·5 and CV events outcomes was observed at PM _2·5 levels above 20 μg/m ³ .

A nonlinear exposure-response relationship between PM2·5 concentration and the incidence of cardiovascular events exists when PM2.5 is higher than the levels recommended by WHO Air Quality Guidelines. Further lowering PM2·5 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.