Background: Air pollution has been recognized as an untraditional risk factor for myocardial infarction (MI). However, the MI risk attributable to long-term exposure to fine particulate matter (PM2.5) is unclear, especially in younger populations, and few studies represented the general population. Methods: We applied the difference-in-differences approach to estimate the relationship between annual PM2.5 exposure and hospitalizations for MI among U.S. residents and further identified potential susceptible subpopulations. All hospital admissions for MI in ten U.S. states over the period 2002-2016 were obtained from the Healthcare Cost and Utilization Project State Inpatient Database. Results: In total, 1,914,684 MI hospital admissions from 8,106 ZIP codes in ten states from 2002 to 2016 were included in this study. We observed a 1.35% (95% CI: 1.11-1.59%) increase in MI hospitalization rate for 1 μg/m3 increase in annual PM2.5 exposure. The estimate was robust to adjustment for surface pressure, relative humidity and co-pollutants. In the population with exposure at or below 12 μg/m3, there was a larger increment of 2.17% (95% CI: 1.79-2.56%) in hospitalization rate associated with 1 μg/m3 increase in PM2.5. Young people (0-34 years) and elderly people (≥75 years) were the two most susceptible age groups. Residents living in more densely populated or poorer areas and individuals with comorbidities were observed to be at a greater risk. Conclusions: This study indicates long-term residential exposure to PM2.5 could lead to increased risk of MI among U.S. general population. The association persists below current standards.

The authors have declared no competing interest.

This study used the inpatient care records from the Healthcare Cost and Utilization Program (HCUP) State Inpatient Database (SID). It did not involve any clinical trial.

This work was made possible by U.S. Environmental Protection Agency (EPA) grant RD-835872. Its contents are solely the responsibility of the grantee and do not necessarily represent the official views of the U.S. EPA. Further, U.S. EPA does not endorse the purchase of any commercial products or services mentioned in the publication. This work was also supported by National Institutes of Health (NIH) grant R01 ES032418-01 and National Institute of Environmental Health Sciences (NIEHS) grant (P30 ES000002).

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