Diesel exhaust, respirable dust, and ischemic heart disease: an application of the parametric g-formula.

Background: Although general population studies of air pollution suggest that particulate matter-diesel exhaust emissions in particular-is a potential risk factor for cardiovascular disease, direct evidence from occupational cohorts using quantitative metrics of exposure is limited. In this study, we assess counterfactual risk of ischemic heart disease (IHD) mortality under hypothetical scenarios limiting exposure levels of diesel exhaust and of respirable mine/ore dust in the Diesel Exhaust in Miners Study cohort. Methods: We analyzed data on 10,779 male miners from 8 nonmetal, noncoal mines-hired after diesel equipment was introduced in the respective facilities-and followed from 1948 to 1997, with 297 observed IHD deaths in this sample. We applied the parametric g-formula to assess risk under hypothetical scenarios with various limits for respirable elemental carbon (a surrogate for diesel exhaust), and respirable dust, separately and jointly. Results: The risk ratio comparing the observed risk to cumulative IHD mortality risk at age 80 under a hypothetical scenario where exposures to elemental carbon and respirable dust are eliminated was 0.79 (95% confidence interval [CI]: 0.64, 0.97). The corresponding risk difference was -3.0% (95% CI: -5.7, -0.3). Conclusion: Our findings, based on data from a cohort of nonmetal miners, are consistent with the hypothesis that interventions to eliminate exposures to diesel exhaust and respirable dust would reduce IHD mortality risk.