The Diesel Exhaust in Miners Study (DEMS) is the largest epidemiological study on the association between occupational exposure to diesel exhaust and lung cancer risk. Study results indicate a strong exposure-response relationship between diesel exhaust exposure, measured as respirable elemental carbon, and lung cancer mortality (Attfield et al. 2012, Silverman et al. 2012). The results, however, seem conflicting insofar as the results of the analysis by standardised mortality ratios (SMR) seem to be not compatible at all with the other results. Moreover, the risk estimators strongly depend on the binary variable work location (“surface-only/ever-underground”), the epidemiological meaning of which is not explained. These concerns have been raised in several publications and even an expert panel, set up by the Health Effects Institute, has evaluated the study results. Yet, the epidemiological meaning of the factor work location remains unexplained (Health Effects Institute Diesel Epidemiology Panel 2015). A synthesis of the published results leads to a new explanation. The key to this hypothesis is the assumption that workers, who switch from surface job to underground job are very likely in much better physical conditions than other surface workers. Therefore, this special form of a healthy-worker-effect could explain the apparent self-contradictory results of the DEMS cohort. A modified analysis by unconditional logistic regression yields as a crude risk estimator adjusted for smoking OR = 0.92 (95% -CI: 0.66–1.30) for miners ever worked underground jobs. Hence, the results of the different approaches for the DEMS cohort are compatible with each other. Moreover, now they are also in line with the findings of the German potash miner cohort (Möhner et al. 2013).
In conclusion, the evidence for a dose-response relationship between diesel motor exhaust and lung cancer in humans seems to be much less than assumed by the IARC.
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