Abstract

Most occupational studies of diesel exhaust have focused primarily on lung cancer. Diesel exhaust is also a risk factor for ischaemic heart disease (IHD) in the ambient environment at concentrations far below those found in dieselized mines, however little is known about the association between occupational exposure to diesel and IHD. We studied IHD mortality (N = 191) in relation to diesel exhaust among 7,122 male, underground workers hired after the start of dieselization in The Diesel Exhaust in Miners Study (DEMS), a NCI/NIOSH cohort study of non-metal miners at eight US mines originally designed to study diesel exhaust and lung cancer mortality. Historical air measurements and surrogate exposure data, along with study industrial hygiene air measurements, were used to develop quantitative estimates of exposure of diesel exhaust (measured as respirable elemental carbon) and respirable dust for each worker in each job-year since dieselization. Cox proportional hazard models with splines were used to examine the shape of the exposure-response curve for cumulative exposure to diesel exhaust and IHD mortality among workers. Baseline hazards were stratified on the type of mine (limestone, potash, trona, and salt) and adjusted for age, birth year, race and the cumulative exposure to respirable dust. The hazard ratios (HR) for ischaemic heart disease from diesel exhaust were log-linear from the smallest exposure to levels of 6 mg/m³-years, the 98th percentile of exposure among the cases and rose to a maximum HR of 1.7 (with wide confidence intervals). The HR at 1.4 mg/m³-years, the mean of cumulative diesel exhaust among the cases, was 1.17 (95% CI: 1.03, 1.30). These results suggest that in addition to increasing the risk of respirable disease among miners, exposure to diesel exhaust underground may also increase the risk of mortality from ischaemic heart disease.