BackgroundMost studies of the association between diesel exhaust exposure and lung cancer suggest
a modest, but consistent, increased risk. However, to our knowledge, no study to date
has had quantitative data on historical diesel exposure coupled with adequate sample
size to evaluate the exposure–response relationship between diesel exhaust and
lung cancer. Our purpose was to evaluate the relationship between quantitative estimates
of exposure to diesel exhaust and lung cancer mortality after adjustment for smoking and
other potential confounders.MethodsWe conducted a nested case–control study in a cohort of 12 315 workers in
eight non-metal mining facilities, which included 198 lung cancer deaths and 562
incidence density–sampled control subjects. For each case subject, we selected up
to four control subjects, individually matched on mining facility, sex, race/ethnicity,
and birth year (within 5 years), from all workers who were alive before the day the case
subject died. We estimated diesel exhaust exposure, represented by respirable elemental
carbon (REC), by job and year, for each subject, based on an extensive retrospective
exposure assessment at each mining facility. We conducted both categorical and
continuous regression analyses adjusted for cigarette smoking and other potential
confounding variables (eg, history of employment in high-risk occupations for lung
cancer and a history of respiratory disease) to estimate odds ratios (ORs) and 95%
confidence intervals (CIs). Analyses were both unlagged and lagged to exclude recent
exposure such as that occurring in the 15 years directly before the date of death (case
subjects)/reference date (control subjects). All statistical tests were two-sided.ResultsWe observed statistically significant increasing trends in lung cancer risk with
increasing cumulative REC and average REC intensity. Cumulative REC, lagged 15 years,
yielded a statistically significant positive gradient in lung cancer risk overall
(P
trend = .001); among heavily exposed workers (ie, above the median of
the top quartile [REC ≥ 1005 μg/m3-y]), risk was approximately three
times greater (OR = 3.20, 95% CI = 1.33 to 7.69) than that among workers
in the lowest quartile of exposure. Among never smokers, odd ratios were 1.0, 1.47 (95%
CI = 0.29 to 7.50), and 7.30 (95% CI = 1.46 to 36.57) for workers with
15-year lagged cumulative REC tertiles of less than 8, 8 to less than 304, and 304
μg/m3-y or more, respectively. We also observed an interaction between
smoking and 15-year lagged cumulative REC (P
interaction = .086) such that the effect of each of these exposures
was attenuated in the presence of high levels of the other.ConclusionOur findings provide further evidence that diesel exhaust exposure may cause lung
cancer in humans and may represent a potential public health burden.