Work status, work hours and health in women with and without children.

OBJECTIVES: The authors studied self-reported health in women with and without children in relation to their work status (employed, student, job seeker or homemaker), work hours and having an employed partner. METHODS: The study group comprised of 6515 women born in 1960-1979 who were interviewed in one of the Swedish Surveys of Living Conditions in 1994-2003. Self-rated health, fatigue and symptoms of anxiety were analysed. RESULTS: Having children increased the odds of poor self-rated health and fatigue in employed women, female students and job seekers. The presence of a working partner marginally buffered the effects. In dual-earner couples, mothers reported anxiety symptoms less often than women without children. Few women were homemakers (5.8%). The odds of poor self-rated health and fatigue increased with increasing number of children in employed women, and in women working 40 h or more. Poor self-rated health was also associated with the number of children in students. Many mothers wished to reduce their working hours, suggesting time stress was a factor in their impaired health. The associations between having children and health symptoms were not exclusively attributed to having young children. CONCLUSIONS: Having children may contribute to fatigue and poor self-rated health particularly in women working 40 h or more per week. Student mothers and job seeking mothers were also at increased risk of poor self-rated health. The results should be noted by Swedish policy-makers. Also countries aiming for economic and gender equality should consider factors that may facilitate successful merging of work and family life.

Arc and resistance welding and tumours of the endocrine glands: a Swedish case-control study with focus on extremely low frequency magnetic fields.

BACKGROUND: Mechanisms for potential effects of extremely low frequency (ELF) magnetic fields on carcinogenesis have not been identified. A potential pathway could be an interaction with the endocrine system. AIMS: To analyse occupational exposure to ELF magnetic fields from welding, and tumours of the endocrine glands. METHODS: This case-control study was based on a cohort with an increased prevalence of high exposed individuals. A total of 174 incident cases of tumours of the endocrine glands, 1985-94, were identified and data were obtained from 140 (80%) of these cases; 1692 controls frequency matched on sex and age were selected, and information on 1306 (77%) individuals was obtained. A short questionnaire was sent to a work administrator at the workplaces of the cases and controls. The exposure assessment was based on questions about job tasks, exposure to different types of welding, and exposure to solvents. RESULTS: There was an overall increased risk for all tumours of the endocrine glands for individuals who had been welding sometime during the follow up. The increased risk was attributable to arc welding; for resistance welding there was no clear evidence of an association. We found an increased risk for the adrenal glands in relation to arc welding, and for the parathyroid glands in relation to both arc welding and resistance welding. An imprecise increase in risk was also noted for tumours of the pituitary gland for arc welding. No confounding effect was found for solvent exposure, and there was no sign of biological interaction. CONCLUSION: The increased risks of endocrine gland tumours related to welding might be explained by exposure to high levels of ELF magnetic fields.

The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies.

The Swedish Twin Registry (STR), which today has developed into a unique resource, was first established in the late 1950s to study the importance of smoking and alcohol consumption on cancer and cardiovascular diseases whilst controlling for genetic propensity to disease. Since that time, the Registry has been expanded and updated on several occasions, and the focus has similarly broadened to most common complex diseases. In the following, we will summarize the content of the database, describe for the first time recent data collection efforts and review some of the principal findings that have come from the Registry.

Cancer incidence and magnetic field exposure in industries using resistance welding in Sweden.

AIMS: To investigate cancer incidence in workers exposed to high levels of extremely low frequency magnetic fields (ELF-MF). METHODS: A cohort based on the engineering industry was established. Industries assumed to use resistance welding in production were chosen in order to increase the prevalence of high exposed subjects and to reduce the influence of confounding factors. All men and women employed in these branches during 1985-94 were selected, 537 692 men and 180 529 women. Occupation, based on census information from 1980, 1985, and 1990, was linked to a job exposure matrix on ELF-MF. Four exposure groups were used by stratifying on mean workday ELF-MF exposure, using the lowest exposure group as reference. Cancer incidence was obtained by linkage to the Swedish Cancer Registry. RESULTS: Men in the very high exposure group showed an increased incidence of tumours of the kidney, pituitary gland, and biliary passages and liver; for these cancer sites an exposure-response relation was indicated. Women in the very high exposure group showed an increased incidence of astrocytoma I-IV, with a clear exposure-response pattern. An association was suggested in the high exposure group only, for cancer of the corpus uteri and multiple myeloma. Decreased risks in the very high exposure group among men were found for cancer of the colon and connective tissue/muscle. CONCLUSIONS: The results on cancer of the liver, kidney, and pituitary gland among men are in accordance with previous observations. Regarding brain tumours and leukaemia, the outcome for women provided further support of an association. The hypothesis of a biological mechanism involving the endocrine system was partly supported.

Changes in sickness absenteeism following the introduction of a qualifying day for sickness benefit--findings from Sweden Post.

AIMS: In 1993, a qualifying day without sickness benefit was introduced to the Swedish sickness benefit system. The aim of the present study is to investigate sickness absenteeism before and after the introduction of the qualifying day, in the light of conditions inside and outside working life. METHODS: The study was based on 1,952 female and 2,229 male employees of Sweden Post. Sickness absence was measured by sickness incidence one year before and one year after the introduction of the qualifying day (sick-leave events/person days at risk). Information about explanatory factors was collected by a postal questionnaire in 1994. RESULTS: A decrease in sickness incidence was observed after the introduction of the qualifying day as well as an increase in the mean duration of sick-leave events. The proportion of long-term sick-leave events (15-365 days) increased; among men this increase was also found in absolute terms. There were no suggestions of economy being an important determinant for reduced sickness incidence. Women with long-term or serious disease did not show a reduction of sickness incidence to the same extent as those without disease, and for men a coherent result was observed. Men with heavy lifting at work more often showed an increase in incidence compared to men without heavy lifting, and the same tendency was found for women. CONCLUSION: The reduction in sickness incidence following the introduction of the qualifying day was fairly independent of different work-related and non-work-related factors. The impact of the qualifying day differed depending on health status and the physical workload.

Occupational sunlight exposure and cancer incidence among Swedish construction workers.

We studied sunlight exposure from outdoor work in relation to cancer, using data from 323,860 men participating in an occupational health service program of the Swedish construction industry. An experienced industrial hygienist assessed the exposure for 200 job tasks. We estimated relative risks (RRs) adjusted for age, smoking, and magnetic field exposure. There was an increased RR in the high-exposure group for myeloid leukemia [RR = 2.0, 95% confidence interval (95% CI) = 1.1-3.6] and lymphocytic leukemia (RR = 1.7, 95% CI = 0.9-3.2). For non-Hodgkin's lymphoma there was a 30% increase in risk in the high-exposure group (95% CI = 0.9-1.9). There was no increased risk of malignant melanoma, except for tumors of the head, face, and neck in the high-exposure group (RR = 2.0, 95% CI = 0.8-5.2), and we also found an increased risk for malignant melanoma of the eye in this group (RR = 3.4, 95% CI = 1.1-10.5). Outdoor workers had no increased risk of nonmelanoma skin cancer. Nevertheless, the RR for lip cancer (squamous cell carcinoma) among the high-exposure group was estimated at 1.8 (95% CI = 0.8-3.7). Among other sites, an increased risk of stomach cancer was suggested in this group (RR = 1.4, 95% CI = 1.0-1.9). The results for lymphoma, leukemia, and possibly also for stomach cancer might reflect a suppression of the immune system from ultraviolet light in outdoor workers.

Breast cancer, occupation, and exposure to electromagnetic fields among Swedish men.

BACKGROUND: Investigations of breast cancer among men may provide clues for environmental and occupational risk factors that may be difficult to study in women, because of confounding or effect modification from reproductive female characteristics. The objective was to estimate occupation-specific risks of male breast cancer and to assess the effect of occupational exposure to extremely low-frequency magnetic fields (ELFMF). METHODS: Standardized incidence ratios were computed for the period 1971-1989 among Swedish men who were 25-59 years of age at start of follow-up and gainfully employed in 1970. Log-linear Poisson models were fitted to adjust for geographical area. A job exposure matrix was used to classify occupational ELFMF exposure. RESULTS: A marked and consistent excess risk was found for machinery repairers. Increased relative risks based on few cases were also noted for librarians/archivists/curators, bank employees, non-specified clerical workers, metal processing workers, tanners/fur dressers, policemen, and custom surveillance officials. The relative risk among subjects with an estimated ELFMF exposure above the first quartile (0.12 microT) was 1.31 (95% confidence interval = 0.94-1.81), without a clear exposure-response pattern. Indications of an exposure-response relationship were found in workers with intermittent ELFMF exposure. CONCLUSIONS: The findings give no clear evidence for an etiological role of ELFMF in the development of breast cancer in men, but suggest that large variations in exposure over the work-day may be associated with an increased risk.

Physical, psychosocial, and organisational factors relative to sickness absence: a study based on Sweden Post.

OBJECTIVE: To analyse incidence of sickness for women and men relative to potential aetiological factors at work-physical, psychosocial, and organisational. METHODS: The study group comprised 1557 female and 1913 male employees of Sweden Post. Sickness absence was measured by incidence of sickness (sick leave events and person-days at risk). Information on explanatory factors was obtained by a postal questionnaire, and incidence of sickness was based on administrative files of the company. RESULTS: Complaints about heavy lifting and monotonous movements were associated with increased risk of high incidence of sickness among both women and men. For heavy lifting, an odds ratio (OR) of 1.70 (95% confidence interval (95% CI) 1.22 to 2.39) among women, and OR 1.70 (1.20 to 2.41) among men was found. For monotonous movements the risk estimates were OR 1.42 (1.03 to 1.97) and OR 1.45 (1.08 to 1.95) for women and men, respectively. Working instead of taking sick leave when ill, was more prevalent in the group with a high incidence of sickness (OR 1.74 (1.30 to 2.33) for women, OR 1.60 (1.22 to 2.10) for men). Overtime work of more than 50 hours a year was linked with low incidence of sickness for women and men. Among women, 16% reported bullying at the workplace, which was linked with a doubled risk of high incidence of sickness (OR 1.91 (1.31 to 2.77)). For men, the strongest association was found for those reporting anxiety about reorganisation of the workplace (OR 1.93 (1.34 to 2.77)). CONCLUSIONS: Certain physical, psychosocial, and organisational factors were important determinants of incidence of sickness, independently of each other. Some of the associations were sex specific.

Mortality among women and men relative to unemployment, part time work, overtime work, and extra work: a study based on data from the Swedish twin registry.

OBJECTIVE: To examine mortality before 70 years of age among women and men relative to unemployment, part time work, overtime work, and extra work. Age, marital status, children, smoking and alcohol habits, use of sleeping pills and tranquilisers, stress, shift work, personality factors, and long lasting or serious illness were taken into account as potential confounding factors. METHODS: The study group comprised a subcohort of the Swedish twin registry, people born in 1926-58. Data were based on a postal questionnaire of 1973 and on information from the Swedish Causes of Death Registry. All subjects reporting a main occupation were selected, 9500 women and 11 132 men, and mortality from all causes during 1973-96 was analysed. The subjects were treated as a sample from the general population regardless of the twinning. RESULTS: Unemployment in 1973 among both women and men showed an association with increased mortality. The adjusted relative risk (RR) (95% confidence interval (95% CI)) was 1.98 (1.16 to 3.38), for women and 1.43 (0.91 to 2.25) for men. For the first 5 years of follow up, a threefold increase in risk was found for men (RR (95% CI) 3.29 (1.33 to 8.17)). The RR declined by time, but remained increased throughout the 24 year study period. In women overtime work of more than 5 hours a week was followed by an increased mortality rate (RR (95% CI) 1.92 (1.13 to 3.25)). A protective effect of moderate overtime work of a maximum 5 hours a week was shown for men (RR (95% CI) 0.58 (0.43 to 0.80)), whereas an increased mortality was indicated for part time work (RR (95% CI) 1.58 (0.91 to 2.77)) and extra work (work outside employment) of more than 5 hours a week (RR (95% CI) 1.29 (0.99 to 1.69)). CONCLUSION: Unemployment and some time aspects of work were associated with subsequent mortality, even when controlling for social, behavioural, work, and health related factors. The idea that losing a job may have less importance for women than for men is not supported by this study.

Breast cancer risk in male twins: joint analyses of four twin cohorts in Denmark, Finland, Sweden and the United States.

To test the hypothesis that in utero exposure to high levels of oestrogen increases the risk of male breast cancer, we followed 115 235 male twins for more than 3.5 million person-years at risk. We observed 11 cases of male breast cancer versus 16.16 expected based on national rates (standardized rate ratio 0.68, 95% confidence interval 0.34-1.22) and conclude that any adverse influence of in utero oestrogen exposure is likely to be small.

Parental occupational exposure to magnetic fields and childhood cancer (Sweden).

OBJECTIVES: To test the hypothesis that parental occupational exposure to magnetic fields before conception and during pregnancy increases the risk of cancer in the offspring. METHODS: The study is designed as a cohort study based on a population of 235,635 children born shortly after two different censuses in Sweden. The children were followed from birth to 14 years and cases of cancer were identified in the Swedish cancer registry. The parents' occupational titles in the censuses were linked to a job-exposure matrix with information about magnetic field levels in different occupations. The cancer incidence among the exposed was compared to that among the unexposed using Cox proportional hazards modeling. RESULTS: There was no association between childhood cancer and maternal occupational magnetic field exposure. Paternal exposure was associated with an increased risk of childhood leukemia, with a relative risk of 2.0 (95% CI 1.1-3.5) for exposures > or = 0.30 microT. A decreased risk was found for brain tumors (RR = 0.5; 95% CI 0.3-1.0). CONCLUSIONS: The results do not support previous findings of an increased risk of childhood brain tumors associated with paternal occupational exposure to magnetic fields. The finding for childhood leukemia has to be interpreted with caution.

Occupational and residential magnetic field exposure and breast cancer in females.

The purpose of this study was to evaluate the effect of occupational magnetic field exposure on breast cancer in females and to combine residential and occupational magnetic field exposure to reduce misclassification. The study was conducted as a case-control study within a population living within 300 meters of transmission lines in Sweden. We identified cases of breast cancer in females from the national cancer registry, and we selected one matched control per case at random. Residential exposure was estimated through calculations of the magnetic fields generated by power lines. We obtained information about occupation from censuses, and the occupations were linked to a job-exposure matrix that was based on magnetic field measurements. For occupational exposure to magnetic fields over 0.25 microT closest in time before diagnosis, the estimated relative risk was 1.0 [96% confidence interval (CI) = 0.6-1.7]. Women below age 50 years at diagnosis had a relative risk of 1.5 (95% CI = 0.6-3.5). For women below 50 years of age who had estrogen receptor-positive breast cancer, there was a relative risk of 3.2 (95% CI = 0.5-18.9). The results for residential and occupational exposures combined showed similar results.

Occupational magnetic field exposure and site-specific cancer incidence: a Swedish cohort study.

OBJECTIVE: Based on 1,596,959 men and 806,278 women, site-specific cancer incidence during 1971 through 1984 was analyzed in relation to occupational magnetic field exposure. The objective was to explore potential associations for cancer diseases beyond those extensively studied before (leukemia and brain tumors). METHODS: Exposure was assessed from Census information on occupations that were linked to a job exposure matrix based on measurements. In a basic analysis, three levels of exposure were used. In addition, subjects with a more definite low exposure were compared with an aggregate of occupations with more definite exposures. RESULTS: Observed associations were weak and there were no evident exposure-response relationships. For all cancer, an approximate 10% increase in risk was seen in the medium and high exposure groups. Several types of cancer were associated with exposure among men, including cancer of the colon, biliary passages and liver, larynx and lung, testis, kidney, urinary organs, malignant melanoma, non-melanoma skin cancer, astrocytoma III-IV. For women, associations were seen for cancer of the lung, breast, corpus uteri, malignant melanoma and chronic lymphocytic leukemia. CONCLUSIONS: In the analysis of occupations with a more definite exposure, the most notable finding for men was an increased risk of testicular cancer in young workers, and for women a clear association emerged for cancer of the corpus uteri. The outcome suggests an interaction with the endocrine/immune system.

Dementia and occupational exposure to magnetic fields.

OBJECTIVES: The purpose of the present report was to assess whether occupational magnetic field exposure is a risk factor for dementia, in particular for Alzheimer's disease. METHODS: Case-control analyses were applied to 77 dementia cases, 55 of whom had Alzheimer's disease, ascertained from the population-based Swedish twin register. Two reference groups were derived, with 228 and 238 persons, respectively. Occupations were linked to a job-exposure matrix based on magnetic field measurements. Primary occupation, last occupation before reference date, and the occupation with the highest magnetic field exposure during the subject's lifetime were evaluated. RESULTS: For primary occupation, all relative risk estimates were close to unity. For last occupation, at the exposure level > or = 0.2 microT, a relative risk was found for dementia estimated at 3.3 [95% confidence interval (95% CI) 1.3-8.6] and 3.8 (95% CI 1.4-10.2) for reference groups 1 and 2, respectively. The relative risk for Alzheimer's disease was estimated at 2.4 (95% CI 0.8-6.9) and 2.7 (95% CI 0.9-7.8), respectively. For the occupation with the highest magnetic field exposure, the relative risk estimates were close to unity for reference group 1 and slightly elevated for reference group 2. The relative risk estimates were greater for the subjects who were younger at onset (< or =75 years). CONCLUSIONS: These results only partially support previous findings, but they indicate that occupational magnetic field exposure may possibly influence the development of dementia.

Occupational and residential magnetic field exposure and leukemia and central nervous system tumors.

Studies of magnetic field exposure and cancer have focused on either residential or occupational exposure. We conducted a case-control study taking into account both exposure sources. We identified leukemia and central nervous system tumor cases and controls from a population living within 300 m of transmission lines in Sweden. We have previously reported results considering residential exposure alone. Here, we evaluate the effect of occupational exposure and of the combined exposures. We estimated residential exposure through calculations of the magnetic fields generated by power lines. We obtained information about occupation from censuses and linked the occupations to a job-exposure matrix based on magnetic field measurements. For occupational exposure of > or = 0.2 microT, we estimated the relative risk for leukemia to be 1.7 [95% confidence interval (CI) = 1.1-2.7]. The increased risk was confined to acute myeloid and chronic lymphocytic leukemia. For residential exposure of > or = 0.2 microT, the relative risk for leukemia was estimated at 1.3 (95% CI = 0.8-2.2), with higher risk estimates for acute and chronic myeloid leukemia. We estimated the relative risk for leukemia among subjects highly exposed both at home and at work to be 3.7 (95% CI = 1.5-9.4). These results provide support for an association between magnetic field exposure and leukemia. Relative risks for nervous system tumors were close to unity.

Occupational exposure to magnetic fields in relation to male breast cancer and testicular cancer: a Swedish case-control study.

Occupational exposure to extremely low-frequency magnetic fields (MF) was studied in 56 male subjects with breast cancer (adenocarcinoma) diagnosed in 1985-91, and 144 subjects with testicular cancer (seminoma and non-seminoma), diagnosed in 1985-87. The cases were compared with 1,121 control subjects from a previous case-control study on MF and cancer. Exposure assessment was based on the job held longest during the decade before diagnosis linked to a job exposure matrix based on MF measurements. The results refer to an estimated average mean of > 0.28 microT (Q4) and > 0.40 microT (P90, part of Q4) with < or = 0.15 microT (Q1) as reference. For breast cancer, the odds ratios (OR) and the 95 percent confidence intervals (CI) were 0.7 (CI = 0.3-1.9) and 0.7 (CI = 0.2-2.3), respectively. For men 60 years or younger, the corresponding estimates were OR = 0.9 (CI = 0.2-4.5) and 1.5 (CI = 0.3-8.3). For testicular cancer, the ORs were 1.3 (CI = 0.7-2.5) and 2.1 (CI = 1.0-4.3), and for men 40 years or younger the ORs were 1.9 (CI = 0.8-4.4) and 3.9 (CI = 1.4-11.2). The results were mainly attributable to non-seminoma, the more malignant type of testicular cancer. Our conclusion is that the results for male breast cancer, based on limited numbers, fail to support the suggested association with MF exposure. The results for testicular cancer gave some support to the hypothesis of a hormonal link between MFs and cancer, and should be further explored.

Magnetic-field Exposures in the Workplace: Reference Distribution and Exposures in Occupational Groups.

Exposures to extremely-low-frequency magnetic fields were assessed by taking personal measurements with a dosimeter calibrated at 50 Hz with a bandwidth of 40-400 Hz. The study group was a population-based random sample of 1,098 Swedish men. Exposures were determined as workday mean, median, maximum, and standard deviation, and the time fraction of the day when exposures exceeded 0.20 µT. For workday means, the 50th percentile was 0.17 µT, and the 75th percentile was 0.27 µT. For median values, the 50th percentile was 0.11 µT and the 75th percentile was 0.16 µT. The strongest correlation (Spearman rank correlation = r&infs;) found was between the workday mean and the fraction of time above 0.20 µT (r&infs; = 0.89). The authors used the same data to estimate exposures for the 100 most common occupations according to the 1990 Swedish census. A minimum of four independent measurements for each occupation was required. Among occupations with low workday mean values were earth-moving machine operator, health care worker, and concrete worker. Among occupations with high workday mean exposures were welder and electrical or electronics engineer or technician. High exposure levels were also found in occupations outside the study base, such as train engine driver and glass, ceramic, or brick worker. Exposures to magnetic fields vary widely, since levels of exposure are strongly affected by factors such as duration of exposure and distance from the source. Large variations often found between individuals within occupations could reflect variations in tasks across different workdays for the particular occupations and/or local conditions such as tools and installations, and/or how the work is organized and performed.

Effect of twinship on incidence of cancer of the testis, breast, and other sites (Sweden).

It has been suggested that cancers of the testis and breast are associated with exposure to estrogens and other hormones in utero. Twin pregnancies have higher levels of pregnancy-associated hormones than singleton pregnancies, and these levels may be higher in dizygotic than in monozygotic twin pregnancies. Through a large population-based study of twins, we assessed the hypothesis that levels of pregnancy-associated hormones have etiologic importance for cancers of the testis, breast, and other sites. The incidence of all cancers among 46,767 members of the Swedish Twin Registry was compared with the incidence among the Swedish general population. We found testicular cancer excess among dizygotic twins (observed/expected[O/E ratio = 2.3, CI = 1.1-4.2) compared with older men (O/E ratio = 1.2, CI = 0.5-2.4). In addition, a substantially elevated incidence of breast cancer was observed in dizygotic twin women aged 20 to 29 years (O/E = 6.7, CI = 2.9-13.1). None of the other age or zygosity groups showed notable elevations in incidence of testicular, breast, or other cancers. We conclude that dizygotic twinship may be associated with cancer of the breast and testis among young adults. These findings support the concept that pregnancy hormones are associated with risk of testicular and breast cancer, although non-hormonal aspects of twin pregnancy that vary with respect to zygosity cannot be excluded as explanatory factors.