Residential radon exposure and lung cancer in Sweden

Lung cancer risk from residential radon: meta-analysis of eight epidemiologic studies

BACKGROUND

Studies of underground miners exposed to radioactive radon and its decay products have found that exposure increases risk of lung cancer. Consequently, when radon was found to accumulate in houses, there was concern about the public health impact from exposure to a known carcinogen. Estimates on the basis of studies of underground miners suggest that indoor radon may account for 6000-36,000 lung cancer deaths each year in the United States. Because of differences between working in underground mines and living in houses, estimates are subject to major uncertainties. Numerous case-control studies were launched to assess directly the lung cancer risk from indoor radon. Some studies report positive or weakly positive findings, while others report no increased risk. Thus, the potential hazard from indoor radon remains answered only indirectly through miner studies, experimental animal studies, and cellular studies.

PURPOSE

To provide more information on the risk of lung cancer from indoor radon, we conducted a meta-analysis of all case-control studies that included at least 200 case subjects each and that used long-term indoor radon measurements.

METHODS

Eight studies were available and included a total of 4263 lung cancer case subjects and 6612 control subjects. From the published results of each study, confounder-adjusted relative risk (RR) estimates and 95% confidence intervals (CIs) for categories of radon concentration were obtained, and weighted linear regression analyses were performed.

RESULTS

The combined trend in the RR was significantly different from zero (two-sided P = .03), and an estimated RR of 1.14 (95% CI = 1.0-1.3) at 150 Bq/m3 was found. An influence analysis indicated that no single study dominated the combined results. The exposure-response trend was similar to model-based extrapolations from miners and to RRs computed directly from miners with low cumulative exposures. However, there were significant differences in the study-specific estimates of the exposure response (two-sided P < .001), which were not explained by study differences in percent of the defined exposure interval covered by radon measurements, mean number of residences per subject, and other factors.

CONCLUSIONS

Meta-analyses are valuable for identifying differences among studies and for summarizing results, but they should be interpreted cautiously when expected RRs are low as with indoor radon exposure, when there is study heterogeneity and where there is the potential for confounding and exposure misclassification. Nonetheless, the results of this meta-analysis suggest that the risk from indoor radon is not likely to be markedly greater than that predicted from miners and indicate that the negative exposure response reported in some ecologic studies is likely due to model misspecification or uncontrolled confounding and can be rejected.

IMPLICATIONS

Until ongoing case-control studies of indoor radon are completed and the data are pooled and analyzed, the studies of underground miners remain the best source of data to use to assess risk from indoor radon. This meta-analysis provides support for their general validity.

The epidemiology of lung cancer: review of risk factors and Spanish data

Lung cancer is the main form of cancer among men both in Spain and in the rest of europe. However, Spanish incidence rates are among the lowest of the European registries, especially for women. In this country, lung cancer mortality increased much more rapidly for men than for women between the fifties and the eighties. This increase was larger for lung cancer than for any other site. The trend of incidence, in Spain as well as in the greatest part of the world, is entirely explained by tobacco consumption, which remains the major risk factor for lung cancer. Occupational radon and asbestos exposures are other important but less extended determinants of lung cancer. Genetic factors could also play a role in the occurrence of the disease. On the other side, a high consumption of fruit and vegetables is protective, but, so far, no single dietary component has been found to be preventive. In this article, we review the major risk factors of lung cancer with an emphasis on Spanish and European data.

Lung cancer, smoking, and environment: a cohort study of the Danish population

OBJECTIVE

The almost twofold difference in lung cancer incidence between people living in Copenhagen and in rural area of Denmark in the 1980s led to public concern; this study was undertaken to assess the effects of air pollution and occupation on lung cancer in Denmark, with control for smoking habits.

DESIGN

Cohort study of national population.

SUBJECTS

People aged 30-64 and economically active in 1970 (927,470 men and 486,130 women).

MAIN OUTCOME MEASURES

Relative risks for lung cancer estimated with multiplicative Poisson modelling of incidence rates.

RESULTS

Differences in smoking habit explained about 60% of the excess lung cancer risk in Copenhagen for men and 90% for women. After control for smoking, workers had double the lung cancer risk of teachers and academics. There was only a small independent effect of region.

CONCLUSION

Smoking is the main factor behind the regional differences in lung cancer incidence in Denmark, and occupational risk factors also seem to have an important role. The outdoor air in Copenhagen around 1970 contained on average 50-80 micrograms/m3 of sulphur dioxide, 80-100 micrograms/m3 total suspended particulate matter, and up to 10 ng/m3 benzo(a)pyrene and had peak values of daily smoke of 120 micrograms/m3. Region had only a small effect on incidence of lung cancer int eh present study, which suggests that an influence of outdoor air pollution on lung cancer is identifiable only above this pollution level.

Radium in drinking water and risk of bone cancer in Ontario youths: a second study and combined analysis

OBJECTIVES

Radium induces bone sarcomas at high doses, but there is controversy about risk at low doses. A previous study in Ontario found an association between the presence of radium in birthplace water supplies and an increased risk of death from bone cancer in young people. An investigation was performed to test the findings of the previous study with an independent group of subjects for whom complete information on radium exposure would be obtained.

METHODS

A population based case-control study (238 cases; 432 controls) was conducted with incident cases of bone sarcoma identified from the Ontario cancer registry. Residential histories were collected by questionnaire and water samples were obtained and analysed for radium content.

RESULTS

There was an association between risk of osteosarcoma and birthplace exposures (odds ratios (ORs) and 90% confidence intervals (90% CIs) 1.77 (1.03-3.00) but not with lifetime measures of exposure. When lifetime exposure was dichotomised, the OR was 1.31 (0.76-2.24) for osteosarcoma. There was no trend with increasing exposure. Bootstrap resampling was used to simulate lifetime doses in a pooled analysis of 1293 subjects from the two Ontario studies. The ORs were 1.38 (1.08-1.73) for all sarcomas, and 1.44 (1.01-1.87) for osteosarcoma. Geometric mean doses in bone were about 26 mRad.

CONCLUSIONS

An association was found between the presence of radium in birthplace water supplies and increased risk of bone sarcoma in two studies. Increased risk was present for lifetime measures of exposure, but the association was not significant, and there was no dose-response trend. Our findings are compatible with the absence of risk at low doses, but they might also reflect inadequate statistical power to measure a true risk at environmental exposure levels. If the increased risk at environmental doses is causal, risk of bone sarcoma is effectively linearly related to dose over five orders of magnitude.

Importance of Radon as a Threat to Public Health

Since the discovery of x rays, the public has shown increasing concern about exposure to radiation. In the mid-1980s, with the dissemination of information about the ubiquitous nature of radon, this concern about radiation exposure has taken on a new perspective. As the general public realizes that exposure to radiation is an unavoidable part of life, questions arise as to how much exposure is acceptable when weighed against the costs of reducing the exposure. Because limited resources are available to protect the public's health and the environment, these resources need to be used wisely. The cost-effectiveness of the various options to lessen the potential adverse health effects from radon must be considered.

How dangerous is low level radiation?

Problems in the theoretical basis for the linear-no threshold theory of radiation carcinogenesis are reviewed, and it is shown that they very strongly suggest that the theory greatly overestimates the risk of low level radiation. A direct test of the theory, based on the radon-lung cancer relationship is described; it strongly reinforces that conclusion. However, it is shown that even if the linear-no threshold theory is valid, the public's fear of low level radiation, at least in some contexts, is grossly exaggerated.

Hazards of ionising radiation: 100 years of observations on man

In November 1895, when Conrad Röntgen serendipitously discovered X-rays, epidemiology was effectively limited to the study of infectious disease. What little epidemiological work was done in other fields was done as part of clinical medicine or under the heading of geographical pathology. The risks from exposure to X-rays and subsequently from other types of ionising radiation were consequently discovered by qualitative association or animal experiment. They did not begin to be quantified in humans until half a century later, when epidemiology emerged as a scientific discipline capable of quantifying risks of non-infectious disease and the scientific world was alerted to the need for assessing the effects of the radiation to which large populations might be exposed by the use of nuclear energy in peace and war.

Potential for bias in epidemiologic studies that rely on glass-based retrospective assessment of radon

Retrospective assessment of exposure to radon remains the greatest challenge in epidemiologic efforts to assess lung cancer risk associated with residential exposure. An innovative technique based on measurement of alpha-emitting, long-lived daughters embedded by recoil into household glass may one day provide improved radon dosimetry. Particulate air pollution is known, however, to retard the plate-out of radon daughters. This would be expected to result in a differential effect on dosimetry, where the calibration curve relating the actual historical radon exposure to the remaining alpha-activity in the glass would be different in historically smoky and nonsmoky environments. The resulting "measurement confounding" can distort inferences about the effect of radon and can also produce spurious evidence for synergism between radon exposure and cigarette smoking.

The causes and prevention of cancer

Epidemiological evidence indicates that avoidance of smoking, increased consumption of fruits and vegetables, and control of infections will have a major effect on reducing rates of cancer. Other factors include avoidance of intense sun exposure, increases in physical activity, and reduction of alcohol consumption and possibly red meat. A substantial reduction in breast cancer is likely to require modification of sex hormone levels, and development of practical methods for doing so is a high research priority. Resolution of the potential protective roles of specific antioxidants and other constituents of fruits and vegetables deserves major attention. Mechanistic studies of carcinogenesis indicate an important role of endogenous oxidative damage to DNA that is balanced by elaborate defense and repair processes. Also key is the rate of cell division, which is influenced by hormones, growth, cytotoxicity, and inflammation, as this determines the probability of converting DNA lesions to mutations. These mechanisms may underlie many epidemiologic observations.

Radiation hormesis - fact or fiction?

Deriving from the Greek verbhormein, which means to stimulate and excite, hormesis literally refers to any kind of stimulation and excitation. As a medical and geomedical term (though of unsettled status) it has a more restricted meaning however, indicating merely the putative or real stimulatory and beneficial effects observed when a biological system is exposed to a low dose of an agent known to be toxic or hazardous at a significantly larger dose. Depending on the type of stimulatory agent, one can speak of chemical or physical hormesis, radiation hormesis being a member of the latter group. The present paper reviews and evaluates the history and origins of the concept of radiation hormesis and its present status - fact or fiction. It is concluded that despite the numerous, sometimes undeniably strong, individual pieces of evidence that have been presented in favour of this phenomenon, the bulk of the evidence is so far not strong enough to establish it as a scientifically proven fact. It is also evident that, instead of speaking of radiation hormesis as an entity, one should pay attention separately to the effects of alpha, beta and gamma radiation, the deleterious and possible beneficial hormetic effects being different in each case.

Attributable risk of lung cancer in lifetime nonsmokers and long-term ex-smokers (Missouri, United States)

A population-based, case-control study of incident lung cancer among women in Missouri (United States) who were lifetime nonsmokers and long-term ex-smokers was conducted between 1986 and 1992. The study included 618 lung cancer cases and 1,402 population-based, age matched controls. Information on lung-cancer risk factors was obtained by interviewing cases, next-of-kin of cases (36 percent and 64 percent of the cases, respectively) and controls. Year-long radon measurements also were sought in every dwelling occupied for the previous five to 30 years. Population attributable risks (PAR) for specific risk factors were computed for all subjects, for lifetime nonsmokers, for long-term ex-smokers, by histologic cell type (i.e., adenocarcinoma cf nonadenocarcinoma) and for direct interviews with case (for living cases) and for next-of-kin interviews (for dead cases or cases too ill to complete an interview). The mean age at lung cancer diagnosis was 71 years, and nearly 50 percent of the lung cancers were histologically confirmed adenocarcinomas. Almost 40 percent of all lung cancers among lifetime nonsmokers and almost 50 percent of lung cancers among all subjects could be explained by the risk factors under study. Dietary intake of saturated fat and nonmalignant lung disease were the two leading identified risk factors for lung cancer among the lifetime nonsmokers, followed by environmental tobacco smoke, and occupational exposures to known carcinogens. A small nonsignificant risk was found for study subjects exposed to median domestic radon concentration of 4 pCi/l (25-year time-weight average).(ABSTRACT TRUNCATED AT 250 WORDS)

Cancer risks from exposure to radon in homes

Exposure to radon and its decay products in mines is a well recognized risk of lung cancer in miners. A large number of epidemiologic studies from various countries are quite consistent in this respect even it the magnitude of the risk differs according to exposure levels. Indoor radon became a concern in the 1970s and about a dozen studies have been conducted since 1979, mainly of the case-control design. From first being of a simple pilot character, the designs have become increasingly sophisticated, especially with regard to exposure assessment. Crude exposure estimates based on type of house, building material and geological features have been supplemented or replaced by quite extensive measurements. Still, exposure assessment remains a difficult and uncertain issue in these studies, most of which indicate a lung cancer risk from indoor radon. Also a recent large scale study has confirmed a lung cancer risk from indoor radon. More recently there are also some studies, mainly of the correlation type, suggesting other cancers also to be related to indoor radon, especially leukemia, kidney cancer, and malignant melanoma, and some other cancers as well. The data are less consistent and much more uncertain than for indoor radon and lung cancer, however; and there is no clear support from studies of miners in this respect.

Bronchial dysplasia induced by radiation in miners exposed to 222Rn progeny

OBJECTIVES

To investigate whether sputum cytology can be used to monitor epithelial cell changes in groups at high risk of lung cancer from exposure to radiation.

METHODS

Dysplasia of bronchial cells was investigated by means of sputum cytology in a group of 434 underground miners. 100 of them were not exposed, and 334 were exposed to 222Rn progeny at cumulative exposures < 450 working level months.

RESULTS

The frequency of dysplasia in the exposed group was significantly higher than that in the not exposed group (P < 0.0001), and an exposure-response relation was found. This relation was different for smokers and non-smokers.

CONCLUSIONS

Possibly the frequencies of dysplasia could be used to assess past exposures of groups of miners. This approach could be applied to cases where data on radiation monitoring are not available or are very scarce.

Cancer mortality in low radon spa area

Recently lower mortality for cancers of all sites was reported among inhabitants in the Misasa spa area, where there is a high radon background. To clarify the effects of radon exposure on cancer mortality, the effects of a hot spring itself on cancer mortality was investigated in the Beppu spa area, which has only a low radon background, and adjacent control areas. For females, the mortalities for cancers of all sites, liver and lung were higher in Beppu than those for all Japan on the basis of the standardized mortality ratio (SMR), while the SMR for all cancers was lower in adjacent areas. For the male inhabitants in both areas the cancer mortalities of all sites were not significantly different from those of all Japan. When we directly compared the most typical spa areas in Beppu and an adjacent control area, a Poisson regression analysis did not show that the relative risk of dying from cancer of all sites was decreased in the spa areas. These results are thus consistent with the view that the lower cancer mortality in the Misasa spa area might be related to exposure to low levels of radon.

Dose-response relationship for radiation carcinogenesis in the low-dose region

Evidence that low-level radiation substantially enhances the effectiveness of repair mechanisms is summarized. This finding destroys the theoretical basis (there is no other basis) for use of a linear-no threshold dose-response relationship to estimate the cancer risk of exposure to low-level radiation. Such a methodology will exaggerate the risk. This conclusion is further supported by epidemiological evidence and by studies of the effects of radon exposure in the home, which are reviewed.

Residential radon exposure and lung cancer--an epidemiological study of Norwegian municipalities

The study is based on a collaboration between the Cancer Registry of Norway, the Norwegian Radiation Protection Authority, and National Radiological Protection Board (NRPB, UK). The association between indoor radon exposure and lung cancer was studied in 427 municipalities. NRPB detectors were sent to 10,000 households, and 7,500 of the detectors were returned. Data from a nation-wide survey of smoking habits in 1964-1965 were available. Data on asbestos exposure were also used in a regression analysis. The reporting to the Cancer Registry of all new cases of cancer is fairly complete, as hospital departments and institutes of pathology are obliged to report all cancer cases. The histologically confirmed lung cancer cases were grouped into squamous-cell carcinoma, small-cell carcinoma, adenocarcinoma and other or non-specified histological types. The age-adjusted rate of lung cancer by histological type was the dependent variable in the regression analysis. A consistent increase in incidence of lung cancer was seen with increasing tobacco consumption, but no positive trend could be shown with increasing radon exposure in the descriptive presentation of the data. In the regression analysis, however, the incidence of small-cell anaplastic lung tumors in females increased significantly with increasing radon exposure. When based on the regression coefficients, the fraction of lung cancers attributable to radon is about 2-4%. However, systematic errors cannot be excluded in an ecological study such as presented here.