Long-term exposure to ambient air pollution and risk of incident acute myocardial infarction in a nationwide register-based cohort study

Objective: The aim of this study was to investigate the association between long-term exposure to ambient air pollution at the residential address and the risk of acute myocardial infarction (AMI) in a younger working population. Methods: The study population included all Danish residents aged 35–50 in 1995 with employment and no previous diagnosis of AMI. Information on AMI was obtained through national registries. We estimated the exposure to fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), elemental carbon (EC) and primary organic aerosols (POA) from 1979 onwards based on the Danish integrated multi-scale air pollution modeling system. Poisson regression models were used to estimate incidence rate ratios (IRR) with 95% confidence intervals (CI) of AMI. Results: 903,415 individuals were included in this cohort, covering almost 20 million person-years of follow-up between 1996 and 2018. In total 35,511 developed AMI. Our main analyses showed a clear exposure-response relationship between cumulative exposure to each of the air pollutants and incident AMI. Exposure was categorized into quartiles (Q1–Q4), with Q1 as reference. The most pronounced association was observed for PM_2.5 with IRRs of 1.08 [95% CI 1.04,1.13], 1.14 [95% CI 1.09,1.20] and 1.24 [95% CI 1.18,1.31] in Q2–Q4 in model 4 (fully adjusted). The associations were observed for both sexes and across age groups. Conclusion: Our findings suggest that long-term exposure to PM_2.5, NO₂, EC, and POA are associated with an increased risk of incident AMI, also pertaining to the younger population (< 55 years).