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Occupational radon exposure and lung cancer mortality: Estimating intervention effects using the parametric G formula (Edwards et al 2014)

Absence of conflict of interest.

Citation

Edwards, J. K., McGrath, L. J., Buckley, J. P., Schubauer-Berigan, M. K., Cole, S. R., & Richardson, D. B. (2014). Occupational radon exposure and lung cancer mortality: Estimating intervention effects using the parametric G formula. Epidemiology, 25(6), 829-834. https://doi.org/10.1097/ede.0000000000000164

Highlights

  • The study’s objective was to examine the impact of three different historical U.S. radon exposure standards on lung cancer mortality.
  • The author used statistical models and data from the Colorado Plateau Uranium Miners cohort to estimate the risk of lung cancer death based on different limits of radon exposure.
  • The study found that all three federal standards that limited radon exposure were associated with lower cumulative lung cancer mortality by age 90. However, tests of statistical significance were not reported.
  • The quality of causal evidence presented in this report is moderate because it is based on a well-implemented nonexperimental design. This means we are somewhat confident that the estimated effects are attributable to the historical radon exposure standards, but other factors might also have contributed.

Features of the Study

The nonexperimental study's overall objective was to examine the effect of radon exposure on lung cancer. The authors used cohort data from a longitudinal study of underground miners to estimate the risk of lung cancer death if U.S. historical radon exposure standards had been in place during the miners’ employment. The Federal radon exposure standards included:

  • Federal Radiation Council’s 1960 recommendation capped radon exposure at two working-level months;
  • Federal Radiation Council’s 1967 recommendation capped radon exposure at one working-level month; and
  • Mine Safety and Health Administration exposure standard adopted in the 1970s capped radon exposure at .33 working-level months.

The study participants include a cohort of 4,137 Colorado Plateau uranium miners. All men worked in an underground uranium mine prior to January 1, 1964 and had a health screening between 1950 and 1960. Miners were followed from the mid-point of their age of the year of their first health screening until death or December 31, 2005. The authors used age as a criterion to form the treatment group and excluded men over 90 years of age resulting in a sample of 4,134 men. The study used statistical modeling to estimate the impacts of the three Federal standards. The models controlled for age, calendar year of cohort entry, race, smoking status, employment and radon exposure. However, the authors did not report tests of statistical significance.

Findings

Health and Safety

  • The study found that decreasing radon exposure levels corresponded to a reduction in lung cancer mortality.
  • The study found that when capping miners' monthly radon exposure to two working-level months, the risk of lung cancer death decreased by 23% and would have prevented 149 lung cancer deaths by age 90.
  • The study found that when capping miners' monthly radon exposure to one working-level month, the risk of lung cancer death decreased by 28% and would have prevented 187 lung cancer deaths by age 90.
  • The study found that when capping miners' monthly radon exposure to .33 working-level months, the risk of lung cancer death decreased by 33% and would have prevented 216 lung cancer deaths by age 90.

Considerations for Interpreting the Findings

While the statistical models controlled for many variables, including age and smoking status, there are other unobserved variables that could impact the findings. Health status, exposure to silica, or differences in smoking status over time could be associated with radon exposure intensity and subsequent lung cancer mortality.

Causal Evidence Rating

The quality of causal evidence presented in this report is moderate because it is based on a well-implemented nonexperimental design. This means we are somewhat confident that the estimated effects are attributable to the historical radon exposure standards, but other factors might also have contributed.

Reviewed by CLEAR

August 2020