Health Effects of Exposure to Radon Time for Reassessment? (1994) / Chapter Skim
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4 Epidemiologic Investigations
4 Epidemiologic Investigations
Pages 51-74
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From page 51... ...
It is therefore not supposing Cat Hose popu~hons of miners have served as a valuable resource for epidemiology studies, and the resuldng database has been used to establish risk estimates for lung cancer that have then been extrapolated to the lower exposure levels found in homes. However, a majority of uranium miners are cigarette-smokers, and the miners are also exposed to silica, arsenic, blasting flumes, and, in some mines, diesel exhaust.
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From page 52... ...
The BEIR IV committee analyzed data on four of the cohortsMalmberget (Sweden) iron miners, Colorado Plateau uranium miners, BeaverIodge uranium miners, and Ontario uranium miners-to develop a risk model.
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From page 53... ...
The studies of Port Radium, Radium HiD, and French uranium miners provided new data on exposures lower than in some of the earlier cohorts.
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From page 54... ...
took He lead in a pooled analysis of data from ~ ~ studies of underground miners, each of which was large (at least 40 lung-cancer deaths) and included estimates of individual exposures to radon progeny.
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From page 55... ...
Various methods were used to estimate exposure to radon progeny. Six studies had some data on cigarette-smoking, and a few had information on exposures in addition to radon progeny, including arsenic and silica.
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From page 56... ...
Over a wide range of total cumulative exposures, lungcancer risk increased as exposure rate declined; that effect was not included in Be BEIR {V committee's model. Although an effect of exposure rate was found in the BEIR IV analysis of data on the Colorado cohort, such an effect was not evident in the three other cohorts, and exposure rate was not considered further by the BEIR IV committee.
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From page 57... ...
The inverse exposure rate has potentially important implications for the use of the miner studies to estimate risk associated with typical indoor exposure levels. However, the pooled analysis does not directly address the exposure-rate range typical of indoor environments, which lies within the lowest categories used in the models discussed below.
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From page 58... ...
was the inclusion of terms expressing an inverse dose-rate effect. However, the range of exposure rates encompassed by the miner studies does not include the usual indoor exposure rates.
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From page 59... ...
Such an assessment would be difficult and would require many assumptions, but it is a highly desirable objective for a Phase ~ (BEIR VI) committee.
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From page 60... ...
The BEIR IV report summarized mortality data from several sources for cancer sites other than the lung. Because most of He individual cohort studies have inadequate statistical power for addressing malignancies other than lung cancer, an additional pooled analysis of the 11 cohorts directed at cancers other than lung cancer has been organized by Sarah Darby at the Imperial Cancer Research Fund Cancer Epidemiology Unit, University of Oxford.
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From page 61... ...
STUDIES OF LOG CANCER IN THE GENERAL ENVIRONMEN r Overview Risk assessments of lung cancer associated with residential radon exposure have been based on extrapolation of estimates obtained from studies of underground miners. Concentrations in the mines were generally much higher than typical concentrations In residences, and factors influencing exposure-dose relations, such as breading and activity patterns, are also expected to be different between Be residential and mining environments.
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From page 62... ...
Those differences necessarily lead to uncertaindes in applying miner-based estimates of risk to the general population, which includes males and females of all ages, both smokers and nonsmokers, who are exposed to the lower levels found in homes. To reduce the uncertainties, epidemiologic investigations designed to estimate the risk associated with indoor radon directly have been undertaken.
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From page 63... ...
The findings of these studies suggested an association of lung cancer with residential radon exposure, but radon had been measured in only one study. Since the BEIR IV committee completed its review, results of additional studies have been reported, and many new studies have been initiated.
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From page 64... ...
Such analyses are needed to obtain the most precise direct quantitative assessment of risk, to evaluate the consistency of findings from different studies, and to achieve sufficient power to address questions related to effect modification by smoking, sex, age at exposure, and other factors. As indicated above, a pooled analysis has already been conducted, and pooled analyses involving additional studies might be available for evaluation by a BEIR VI committee.
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From page 66... ...
evaluated the sample sizes required in a casecontrol study to detect an association between lung cancer and residential radon exposure under the assumption predictions based on underground miners are correct, to detect Hat the quantitative effect is half that predicted from underground miners, and to detect a departure from an additive interaction between smoking and radon exposure if the true interaction is multiplicative rather Pan achieve. Their sample-size estimates for a case-control study assume that the distribution of exposure in the population being studied is similar to that described by Nero and colleagues (Nero et al., 1986)
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From page 67... ...
Even ~ the most straightforward scenario in which subjects have lived Weir whole life in a single residence for which long-term exposure measurements are available, there are uncertainties In exposure estimates. For example, the measurements might not adequately reflect conditions In the home over the full period of residence, the amount of time the subject spent in different rooms in the home cannot be determined precisely, and exposures received in places other man the home cannot be estimated.
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From page 68... ...
Even if the information on potential confounding factors is equally valid for cases and controls, data on smoking and other risk factors are not likely to be sufficiently detailed and accurate to permit complete adjustment in analyses. Like exposure measurement error, potential confounding introduces additional uncertainty that is not reflected in usual statistical confidence limits.
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From page 69... ...
In eight of the studies, lung-cancer rates were compared for two or more groups defined by exposure status, and seven were regression studies in which rates were modeled as a function (usually linear3 of exposure. Exposure estimates used in these studies included both surrogate measures, such as the geologic charactenshcs of an area, and estimates based on current measurements of indoor radon from samples of homes in ~ area.
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From page 70... ...
The need to use groups on which vim statistics are available can obscure much of the variability in indoor radon exposure and lead to low statistical power for detecting effects, even if the average exposures are assessed correctly. Estimation of exposure from surrogate measures or from sampled homes is likely to reduce power still further and might also introduce bias.
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From page 71... ...
Radon In~lucecl Cancers Other than lacing Cancer Ecologic studies by Hen shaw and colleagues (1990) examined average radon exposures and disease rates for leukemia and other cancers in 14 counmes and in regions of the United Kingdom and Canada.
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From page 72... ...
The results from miner studies have increased our knowledge of the association between radon-progeny exposure and lung cancer risk, including an increase in the populalion database, the introduction of new information in humans first exposed as children, and information regarding the potential role of over agents and nonmalignant respiratory disease in causing lung cancer. Results of one of these studies ~aurer et al., 1993)
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From page 73... ...
reassessment, but the committee recognizes that the results of several studies will not be completed in lime to be available to the Phase ~ committee. Ecologic studies of other cancers and indoor radon exposure have been also published (Stidley and Samet, 1993)
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From page 74... ...
studies reported Bus far have generally Ben consistent win estimates based on extrapolation from data on underground miners but have not provided enough precision to mie out He possibility of no risk or of risks that are substandally larger than those obtained through extrapolation. The Phase ~ committee should determine the potential role of current and future case-control studies for validating risk models based on miners and more generally for developing risk models of residenhal exposure to radon.
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