Source-Specific Air Pollution Including Ultrafine Particles and Risk of Myocardial Infarction: A Nationwide Cohort Study from Denmark

BACKGROUND: Air pollution is negatively associated with cardiovascular health. Impediments to efficient regulation include lack of knowledge about which sources of air pollution contributes most to health burden and few studies on effects of the potentially more potent ultrafine particles (UFP). OBJECTIVE: The authors aimed to investigate myocardial infarction (MI) morbidity and specific types and sources of air pollution. METHODS: We identified all persons living in Denmark in the period 2005–2017, age [Formula: see text] y and never diagnosed with MI. We quantified 5-y running time-weighted mean concentrations of air pollution at residencies, both total and apportioned to traffic and nontraffic sources. We evaluated particulate matter (PM) with aerodynamic diameter [Formula: see text] ([Formula: see text]), [Formula: see text] (UFP), elemental carbon (EC), and nitrogen dioxide ([Formula: see text]). We used Cox proportional hazards models, with adjustment for time-varying exposures, and personal and area-level demographic and socioeconomic covariates from high-quality administrative registers. RESULTS: In this nationwide cohort of 1,964,702 persons (with [Formula: see text] person-years of follow-up and 71,285 cases of MI), UFP and [Formula: see text] were associated with increased risk of MI with hazard ratios (HRs) per interquartile range (IQR) of 1.040 [95% confidence interval (CI): 1.025, 1.055] and 1.053 (95% CI: 1.035, 1.071), respectively. HRs per IQR of UFP and [Formula: see text] from nontraffic sources were similar to the total (1.034 and 1.051), whereas HRs for UFP and [Formula: see text] from traffic sources were smaller (1.011 and 1.011). The HR for EC from traffic sources was 1.013 (95% CI: 1.003, 1.023). [Formula: see text] from nontraffic sources was associated with MI ([Formula: see text]; 95% CI: 1.034, 1.062) but not from traffic sources. In general, nontraffic sources contributed more to total air pollution levels than national traffic sources. CONCLUSIONS: [Formula: see text] and UFP from traffic and nontraffic sources were associated with increased risk of MI, with nontraffic sources being the dominant source of exposure and morbidity. https://doi.org/10.1289/EHP10556