Previous results from the Diesel Exhaust in Miners Study (DEMS) demonstrated a positive exposure-response relation between lung cancer and respirable elemental carbon (REC), a key surrogate for diesel exhaust exposure. Two issues have been raised regarding DEMS: (i) the use of historical carbon monoxide (CO) measurements to calibrate models used for estimating historical exposures to REC in the DEMS exposure assessment; and (ii) potential confounding by radon. The authors developed alternative REC estimates using models that did not rely on CO for calibration, but instead relied on estimated use of diesel equipment, mine ventilation rates and changes in diesel engine emission rates over time. These new REC estimates were used to quantify cumulative REC exposure for each subject in the nested case-control study. The authors conducted conditional logistic regression to estimate odds ratios (ORs) and 95% confidence intervals for lung cancer. To evaluate the impact of including radon as a potential confounder, ORs for average REC intensity were estimated and adjusted for cumulative radon exposure in underground miners. Validation of the new REC exposure estimates indicated that they overestimated historical REC by 200-400%, compared with only 10% for the original estimates. Effect estimates for lung cancer using these alternative REC exposures or adjusting for radon typically changed by <10% when compared with the original estimates. The authors concluded that these results emphasise the robustness of the DEMS findings, support the use of CO for model calibration and confirm that radon did not confound the DEMS estimates of the effect of diesel exposure on lung cancer mortality.
Full Source: Vermeulen R, Portengen L, Lubin J, Stewart P, Blair A, Attfield MD, Silverman DT.
; Full Source: International Journal of Epidemiology. 2019 Sep 20. pii: dyz189. doi: 10.1093/ije/dyz189. [Epub ahead of print]