Mortality from diseases other than cancer following low doses of ionizing radiation: results from the 15-Country Study of nuclear industry workers.

BACKGROUND: Ionizing radiation at very high (radio-therapeutic) dose levels can cause diseases other than cancer, particularly heart diseases. There is increasing evidence that doses of the order of a few sievert (Sv) may also increase the risk of non-cancer diseases. It is not known, however, whether such effects also occur following the lower doses and dose rates of public health concern. METHODS: We used data from an international (15-country) nuclear workers cohort study to evaluate whether mortality from diseases other than cancer is related to low doses of external ionizing radiation. Analyses included 275 312 workers with adequate information on socioeconomic status, over 4 million person-years of follow-up and an average cumulative radiation dose of 20.7 mSv; 11 255 workers had died of non-cancer diseases. RESULTS: The excess relative risk (ERR) per Sv was 0.24 [95% CI (confidence intervals) -0.23, 0.78] for mortality from all non-cancer diseases and 0.09 (95% CI -0.43, 0.70) for circulatory diseases. Higher risk estimates were observed for mortality from respiratory and digestive diseases, but confidence intervals included zero. Increased risks were observed among the younger workers (attained age <50 years, identified post hoc) for all groupings of non-cancer causes of death, including external causes. It is unclear therefore whether these findings reflect real effects of radiation, random variation or residual confounding. CONCLUSIONS: The most informative low-dose radiation study to date provides little evidence for a relationship between mortality from non-malignant diseases and radiation dose. However, we cannot rule out risks per unit dose of the same order of magnitude as found in studies at higher doses.

The 15-Country Collaborative Study of Cancer Risk Among Radiation Workers in the Nuclear Industry: design, epidemiological methods and descriptive results.

Radiation protection standards are based mainly on risk estimates from studies of atomic bomb survivors in Japan. The validity of extrapolations from the relatively high-dose acute exposures in this population to the low-dose, protracted or fractionated environmental and occupational exposures of primary public health concern has long been the subject of controversy. A collaborative retrospective cohort study was conducted to provide direct estimates of cancer risk after low-dose protracted exposures. The study included nearly 600,000 workers employed in 154 facilities in 15 countries. This paper describes the design, methods and results of descriptive analyses of the study. The main analyses included 407,391 nuclear industry workers employed for at least 1 year in a participating facility who were monitored individually for external radiation exposure and whose doses resulted predominantly from exposure to higher-energy photon radiation. The total duration of follow-up was 5,192,710 person-years. There were 24,158 deaths from all causes, including 6,734 deaths from cancer. The total collective dose was 7,892 Sv. The overall average cumulative recorded dose was 19.4 mSv. A strong healthy worker effect was observed in most countries. This study provides the largest body of direct evidence to date on the effects of low-dose protracted exposures to external photon radiation.

The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks.

A 15-Country collaborative cohort study was conducted to provide direct estimates of cancer risk following protracted low doses of ionizing radiation. Analyses included 407,391 nuclear industry workers monitored individually for external radiation and 5.2 million person-years of follow-up. A significant association was seen between radiation dose and all-cause mortality [excess relative risk (ERR) 0.42 per Sv, 90% CI 0.07, 0.79; 18,993 deaths]. This was mainly attributable to a dose-related increase in all cancer mortality (ERR/Sv 0.97, 90% CI 0.28, 1.77; 5233 deaths). Among 31 specific types of malignancies studied, a significant association was found for lung cancer (ERR/Sv 1.86, 90% CI 0.49, 3.63; 1457 deaths) and a borderline significant (P = 0.06) association for multiple myeloma (ERR/Sv 6.15, 90% CI <0, 20.6; 83 deaths) and ill-defined and secondary cancers (ERR/Sv 1.96, 90% CI -0.26, 5.90; 328 deaths). Stratification on duration of employment had a large effect on the ERR/Sv, reflecting a strong healthy worker survivor effect in these cohorts. This is the largest analytical epidemiological study of the effects of low-dose protracted exposures to ionizing radiation to date. Further studies will be important to better assess the role of tobacco and other occupational exposures in our risk estimates.

Comparison of temporal changes in U.S. and Swedish lung cancer, 1950-51 to 1981-82.

A comparison was made of temporal changes in lung cancer risk for the U.S. white and Swedish populations from 1950-51 to 1981-82 with the use of both life-table- and cohort-specific proportional hazard models to illustrate different features of the time series. Marked differences were noted for the two populations; Swedish lung cancer risks were generally lower than those in the United States. Sex-specific analyses were conducted that showed that Swedish males had a mortality rate roughly half that for U.S. males over the entire period. In contrast, U.S. white female mortality rates, though roughly equal to those for Swedish females in 1950-51, experienced a relatively more rapid increase; their rates were double the Swedish rates by 1980. The factors contributing to these patterns, such as marked cohort differences in risk, are identified by the various stages of analysis.

Silica dust and lung cancer: results from the Nordic occupational mortality and cancer incidence registers.

Autopsy studies of the relationship between silicosis and lung cancer have been mainly negative; but recent epidemiologic studies have indicated a positive association, and an excess lung cancer risk has been observed in some occupational groups with exposure to silica dust. For the further shedding of light on the possible association between silica dust and lung cancer, analysis was made on mortality and cancer incidence data available in census-based record linkage studies from the Nordic countries for males in occupational groups with potential exposure to silica dust. The study showed an excess lung cancer risk for foundry workers in all the Nordic countries and for miners in Sweden. These results were consistent with findings from previous in-depth epidemiologic studies. The lung cancer risk did not differ significantly from that of the respective national populations for males working in excavation; stone quarries; sand and gravel pits; and glass, porcelain, ceramic, and tile manufacture. Stonecutters, who are probably not exposed to known lung carcinogens at the workplace but in some places to high concentrations of silica dust, showed a significant excess lung cancer risk in both Finland and Denmark. Excess lung cancer risks furthermore were seen for Finish miners, for Finnish males in excavation work, and for Danish glassworkers.

Occupational risks for pleural mesothelioma in Sweden, 1961-79.

From national population-based registries linking cancer incidence from 1961 to 1979 with 1960 census data on industry and occupation for all employed individuals in Sweden, a systematic assessment was made of pleural mesothelioma occurrence according to occupational and industrial classifications. There were 318 cases of pleural mesothelioma recorded during the 19-year follow-up period among males employed in 1960, with significant variation by industrial and occupational categorizations. The observed number of pleural mesotheliomas for men employed in the sugar refining, cellulose, wood and pulp, shipbuilding, and railroad equipment manufacturing industries was more than three times the number expected. Occupations with at least twofold excess of mesotheliomas included the craftsman categories of plumbers, mechanics and repairmen, electricians, painters, tire makers, and stationary equipment operators. Our findings are consistent with available data relating mesothelioma to occupational asbestos exposure in other countries, although unexpected associations were found that deserve further epidemiologic study.

Occupational risks for intracranial gliomas in Sweden.

With the use of the Cancer-Environment Registry, which links cancer incidence for the years 1961-79 with 1960 census information on occupation for all employed individuals in Sweden, a systematic population-based assessment according to employment classifications was made of the occurrence of intracranial gliomas. Statistically significant (P less than .05) increases in the incidence of intracranial gliomas were observed among several professional and white-collar occupations, possibly due in part to higher levels of diagnosis and reporting of this particular neoplasm. Significantly elevated rates were noted among male dentists, agricultural research workers, and public prosecutors and among female physicians and employees in the health care industry. For blue-collar workers, significant excesses were found among welders and metal cutters; glass, porcelain, or ceramic workers; cellulose plant employees; brick and tile workers; and women employed in the wool industry. Several findings of this survey may represent new clues to the etiology of intracranial gliomas, while other findings support observations reported in previous studies.

Occupational risks for bladder cancer among men in Sweden.

With the use of the Swedish Cancer-Environment Registry, census data on employment in 1960 were linked with registry data on bladder cancer during 1961-79. This hypothesis-generating study revealed for the first time associations between bladder cancer and employment in pulp and fiberboard manufacturing, in rope and twine making, and work as a dental technician. Statistically significant increases in risk were also found for several occupations previously associated with bladder cancer, including barbers and beauticians, artistic painters, toolmakers and machinists, and physicians, and employment in butcher shops, industrial chemical making, apparel manufacturing, and plumbing. Etiologic inferences cannot be made from this investigation, but the findings from this large national resource provide further clues to the occupational determinants of bladder cancer.

Registry-based analysis of occupational risks for primary liver cancer in Sweden.

A systematic evaluation was made of the occurrence of microscopically confirmed primary liver cancer (International Classification of Disease, 7th Rev., 155.0) among men by industrial and occupational classification using the Cancer-Environment Registry, which links cancer incidence (1961-1979) and census data (1960) on industry and occupation for all employed persons in Sweden. A number of blue collar jobs were found to be significantly associated with primary liver cancer, including men employed in breweries, slaughterhouses, grain mills, shoe fabrication, basic industrial chemicals, plumbing and pipefitting, and insulation work. Although brewery workers and several white collar and service employment categories had significantly increased risks, the influence of alcohol intake was suggested by a parallel mortality analysis showing that most categories had excesses of liver cirrhosis and alcoholism. While often consistent with previous studies, the findings of this registry-based survey should be considered primarily as hypothesis generating in nature.

Register epidemiology studies of recent cancer trends in selected workers.

The Swedish Cancer Environment Register (CER) was used to analyze occupational risks of cancer over time. Using expanded time coverage (1961-1984) and two census-based sources in employment information, risk in the work environment was evaluated for a 24-year period for pleural mesothelioma, nasal adenocarcinoma, and non-melanotic skin cancer. Standardized incidence ratios (SIRs) for pleural mesotheliomas were found to increase among plumbers and pipefitters over this period, whereas those for mechanics, electricians, painters, and paperhangers remained relatively stable. Risk for nasal adenocarcinoma among cabinet makers remained exceedingly high over the 24-year period and SIRs for other kinds of woodworkers moderately increased during the same time. Excess skin cancer risk among physicians declined over the period. Reasons for these trends are discussed as well as the limitations and potential of register epidemiology in the evaluation of cancer trends in the work environment.

Exposure to extremely low frequency electromagnetic fields and the risk of malignant diseases--an evaluation of epidemiological and experimental findings.

Epidemiological and experimental studies concerning extremely low frequency electromagnetic field exposure and malignant diseases published up to 1 July 1994 were evaluated to assess the possible carcinogenicity of electromagnetic fields and the scientific basis for environmental and occupational standard setting. We concluded that there are possible associations between (i) an increased risk of leukaemia in children and the existence of, or distance to, power lines in the vicinity of their residence, (ii) an increased risk of chronic lymphatic leukaemia and occupational exposure to low frequency electromagnetic fields and (iii) an increased risk of breast cancer, malignant melanoma of the skin, nervous system tumours, non-Hodgkin lymphoma, acute lymphatic leukaemia or acute myeloid leukaemia and certain occupations. There is no scientific basis for occupational or environmental standard setting for low frequency electric or magnetic fields.

Increased cancer incidence in physicians, dentists, and health care workers.

Some earlier reports have indicated increased incidence or mortality of specific tumor types in various health care professions. In this study we have evaluated cancer incidence in physicians, dentists, and other health care workers using the Swedish Cancer Environment Register (CER), which was formed by record-linkage between the 1970 census on current occupation and Cancer Register incidence data in 1971-84. In all three profession categories studied an increased risk was found, as well for all malignant tumors combined, as for specific tumor types regarding the different occupations. Possible etiological factors responsible for these risks are discussed.

Occupation and prostate cancer risk in Sweden.

To provide new leads regarding occupational prostate cancer risk factors, we linked 36,269 prostate cancer cases reported to the Swedish National Cancer Registry during 1961 to 1979 with employment information from the 1960 National Census. Standardized incidence ratios for prostate cancer, within major (1-digit), general (2-digit), and specific (3-digit) industries and occupations, were calculated. Significant excess risks were seen for agriculture-related industries, soap and perfume manufacture, and leather processing industries. Significantly elevated standardized incidence ratios were also seen for the following occupations: farmers, leather workers, and white-collar occupations. Our results suggest that farmers; certain occupations and industries with exposures to cadmium, herbicides, and fertilizers; and men with low occupational physical activity levels have elevated prostate cancer risks. Further research is needed to confirm these findings and identify specific exposures related to excess risk in these occupations and industries.

Occupational risks for cutaneous melanoma among men in Sweden.

A population-based linked-registry was used to evaluate incidence of malignant melanoma of the skin among Swedish men by industry and occupation. There were 3850 cutaneous melanoma cases identified in the 19-year follow-up of men employed in 1960. New associations were observed for men employed in the breweries and malt-processing industry and in shoe fabrication from leather and skins. Several findings supported associations previously reported in other countries, including an excess risk among workers in basic chemical production and the printing industry and among professional, technical, and white-collar workers. Risk overall was not increased among farmers, despite a significant excess of melanoma of the face, neck, and scalp. Although this linked registry analysis lacked information about specific agents, duration of employment, and occupational and recreational sun exposures, it did provide leads for new associations and confirmed previous ones. Nevertheless, because of these limitations, etiologic clues must be interpreted cautiously.

Cancer among farmers. A review.

During the performance of routine tasks farmers may come in contact with a variety of substances, including pesticides, solvents, oils and fuels, dusts, paints, welding fumes, zoonotic viruses, microbes, and fungi. Because some of these substances are known or suspected carcinogens, the epidemiologic literature regarding cancer risks concerning farmers has been reviewed. Farmers had consistent deficits for cancers of the colon, rectum, liver, and nose. The deficits for cancer of the lung and bladder were particularly striking, presumably due to less frequent use of tobacco among farmers than among people in many other occupational groups. Malignancies frequently showing excesses among farmers included Hodgkin's disease, leukemia, non-Hodgkin's lymphoma, multiple myeloma, and cancers of the lip, stomach, prostate, skin (nonmelanotic), brain, and connective tissues. The etiologic factors that may contribute to these excesses in the agricultural environment have not been identified. Detailed, analytic epidemiologic studies that incorporate environmental and biochemical monitoring are needed to clarify these associations.

A register-epidemiology study on cancer among Swedish printing industry workers.

The Swedish Cancer Environment Registry, a population-based Cancer Registry, has been supplemented with 1960 census data on occupation and industry. This information system was used to generate hypotheses on occupational high-cancer-risk groups and to discuss some methodological problems connected with register epidemiology. By successive exclusion of parts of the original population of printing industry workers with excess risks of lung and cervical cancer it was possible to consider similarities and differences between subgroups. Risk estimates from three different standardization methods agreed well for populations with more than 50 cases. Regional adjustment helped arrive at interpretable risk estimates. The excess risk of cervical cancer disappeared when gainfully employed persons and blue-collar workers were used for reference. After the exclusion procedure there was an excess risk of lung cancer among typographers and lithographers in printing enterprises, especially in some birth-cohorts, due possibly to working exposure environment.

Risk for cancer of the pharynx and oral cavity among male painters in the Nordic countries.

In an effort to evaluate a hypothesis raised by findings in Denmark that painters might experience an increased risk for pharyngeal and oral cancer, data were collected about these cancers among painters in Norway, Sweden, and Finland. The possible confounding effects of alcohol and tobacco were gauged by collecting data about cancer of the lung, larynx, esophagus, liver, and bladder, and about mortality from liver cirrhosis. Consistently increased risks for lung cancer among painters were found. The risks for cancer of the oral cavity and/or pharynx were increased in Norway, Sweden, and Finland, but not to the same extent as was observed in Denmark. The risks for cancer of the esophagus were slightly increased as were the risks for cancer of the liver and for cirrhosis of the liver in Denmark and Finland. The data from Norway, Sweden, and Finland could thus neither substantiate nor disprove the hypothesis that painters may experience an increased risk for cancer of the pharynx and oral cavity as a result of occupational exposures.

Multiple myeloma and occupation in Sweden.

The occurrence of multiple myeloma by occupational and industrial category was systematically assessed using the Swedish Cancer-Environment Registry, which links cancer incidence (1961-1979) with occupational data from the 1960 census. Incidence of multiple myeloma was significantly increased for a number of occupational groups such as farmers, smelter and metallurgy workers, and miners-quarrymen-rock blasters. Although caution must be applied in drawing causal inferences, this national linked-registry analysis may provide clues to the environmental determinants of multiple myeloma.