Long-term Exposure to Ambient PM2.5and Hospitalizations for Myocardial Infarction among U.S. Residents: A Difference-in-Differences Analysis

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 (PM 2.5 ) 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 PM 2.5 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/m 3 increase in annual PM 2.5 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/m 3 , there was a larger increment of 2.17% (95% CI: 1.79-2.56%) in hospitalization rate associated with 1 μg/m 3 increase in PM 2.5 . 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 PM 2.5 could lead to increased risk of MI among U.S. general population. The association persists below current standards. Clinical Perspective What is new? Long-term exposure to PM 2.5 increased the risk of myocardial infarction in the general U.S. population. Young individuals aged 0-34 years had the highest relative risk from long-term exposure to PM 2.5 , and elderly people aged ≥75 years were the second most susceptible to the effects. Individuals with iron deficiency anemia, psychosis, and renal failure were more susceptible to the long-term effects of PM 2.5 on MI. What are the clinical implications? Long-term PM 2.5 exposure is one of the important modifiable environmental risk factors for myocardial infarction, therefore, air pollution control and behavioral interventions should be taken to prevent the occurrence of myocardial infarction.