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Background:

Air pollution exposure has been linked to coronary heart disease, although evidence on ${\mathrm{PM}}_{2.5}$ and myocardial infarction (MI) incidence is mixed.

Objectives:

This prospective cohort study aimed to investigate associations between long-term exposure to air pollution and MI incidence, adjusting for road traffic noise.

Methods:

We used data from the nationwide Danish Nurse Cohort on 22,882 female nurses ($>44\text{years}$ of age) who, at recruitment in 1993 or 1999, reported information on cardiovascular disease risk factors. Data on MI incidence was collected from the Danish National Patient Register until the end of 2014. Annual mean concentrations of particulate matter (PM) with a diameter $<2.5{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ (${\mathrm{PM}}_{2.5}$), ${\mathrm{PM}}_{10}$, nitrogen dioxide (${\mathrm{NO}}_2$), and nitrogen oxides (${\mathrm{NO}}_{\mathrm{x}}$) at the nurses’ residences since 1990 (${\mathrm{PM}}_{10}$ and ${\mathrm{PM}}_{2.5}$) or 1970 (${\mathrm{NO}}_2$ and ${\mathrm{NO}}_{\mathrm{x}}$) were estimated using the Danish Eulerian Hemispheric Model/Urban Background Model/AirGIS (DEHM/UBM/AirGIS) dispersion model. We used time-varying Cox regression models to examine the association between 1- and 3-y running means of these pollutants, as well as 23-y running means of ${\mathrm{NO}}_2$ and ${\mathrm{NO}}_{\mathrm{x}}$, with both overall and fatal incident MI. Associations were explored in three progressively adjusted models: Model 1, adjusted for age and baseline year; Model 2, with further adjustment for potential confounding by lifestyle and cardiovascular disease risk factors; and Model 3, with further adjustment for road traffic noise, modeled as the annual mean of a weighted 24-h average (${\mathrm{L}}_{\text{den}}$).

Results:

Of the 22,882 women, 641 developed MI during a mean follow-up of 18.6 y, 121 (18.9%) of which were fatal. Reported hazard ratios (HRs) were based on interquartile range increases of 5.3, 5.5, 8.1, and $11.5{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ for ${\mathrm{PM}}_{2.5}$, ${\mathrm{PM}}_{10}$, ${\mathrm{NO}}_2$, and ${\mathrm{NO}}_{\mathrm{X}}$, respectively. In Model 1, we observed a positive association between a 3-y running mean of ${\mathrm{PM}}_{2.5}$ and an overall incident MI with an $\text{HR}=$ 1.20 (95% CI: 1.07, 1.35), which attenuated to $\text{HR}=$ 1.06 (95% CI: 0.92, 1.23) in Model 2. In Model 1 for incident fatal MI, we observed a strong association with a 3-y running mean of ${\mathrm{PM}}_{2.5}$, with an $\text{HR}=$ 1.69 (95% CI: 1.33, 2.13), which attenuated to $\text{HR}=$ 1.35 (95% CI: 1.01, 1.81) in Model 2. Similar associations were seen for ${\mathrm{PM}}_{10}$, with 3-y, Model 2 estimates for overall and fatal incident MI of $\text{HR}=$ 1.06 (95% CI: 0.91, 1.23) and $\text{HR}=$ 1.35 (95% CI: 1.01, 1.81), respectively. No evidence of an association was observed for ${\mathrm{NO}}_2$ or ${\mathrm{NO}}_{\mathrm{x}}$. For all pollutants, associations in Model 2 were robust to further adjustment for road traffic noise in Model 3 and were similar for a 1-y running mean exposure.

Conclusions:

We found no association between long-term exposure to ${\mathrm{PM}}_{2.5}$, ${\mathrm{PM}}_{10}$, ${\mathrm{NO}}_2$, or ${\mathrm{NO}}_{\mathrm{x}}$ and overall MI incidence, but we observed positive associations for ${\mathrm{PM}}_{2.5}$ and ${\mathrm{PM}}_{10}$ with fatal MI. We present novel findings that the association between PM and MI incidence is robust to adjustment for road traffic noise. https://doi.org/10.1289/EHP5818