Birgitta Floderus

Occupational exposure to electromagnetic fields in relation to leukemia and brain tumors: a case-control study in Sweden

Occupational exposure to low-frequency electromagnetic fields (EMF) was studied in 250 leukemia patients and 261 brain-tumor cases, diagnosed in 1983–87 and compared with a control group of 1,121 randomly selected men, from the mid-region of Sweden, 1983–87. We based the exposure assessment on measurements from 1,015 different workplaces. On the basis of the job held longest during the 10-year period before diagnosis, we found an association between the average, daily, mean level of EMF and chronic lymphocytic leukemia (CLL). The risk increased with increasing level of exposure. The odds ratios (OR) and the 95 percent confidence interval (CI) for three consecutive levels of exposure were: 1.1 (CI=0.5–2.3); 2.2 (CI=1.1–4.3); 3.0 (CI=1.6–5.8), respectively. No association was observed for acute myeloid leukemia (OR=1.0, CI=0.5–1.8; OR=0.8, CI=0.4–1.6; OR=1.0, CI=0.6–1.9). For brain tumors, the corresponding risk estimates were 1.0 (CI=0.7–1.6); 1.5 (CI=1.0–2.2); 1.4 (CI=0.9–2.1). Different EMF indices were tested. Tasks with frequent or large variations between high and low field-densities (high standard deviation) were more common among CLL subjects. For brain tumors, a prolonged high level (high median values) showed the strongest association. Confounding by place of residence, smoking, benzene, ionizing radiation, pesticides, and solvents was evaluated, and these factors did not seem to have a decisive influence on the associations. We also analyzed other potential sources of bias. For CLL, there were indications of an excess number of low-exposure subjects among non-responders, which, to some extent, may have enhanced but not caused the risk estimates obtained. Our conclusion is that the study supports the hypothesis that occupational EMF exposure is a hazard in the development of certain cancers.

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.

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=1.6, 95 percent confidence interval [CI]=1.0–2.6) that was greater for men younger than 35 years (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.

Unemployment and Early Cause-Specific Mortality: A Study Based on the Swedish Twin Registry

OBJECTIVES We investigated the association between unemployment and early cause-specific mortality to determine whether the relationship was modified by other risk indicators. METHODS Female and male twins (n=20632) were followed with regard to mortality from 1973 through 1996. Questionnaire data from 1973 were used to obtain information on experience of unemployment and on social, behavioral, health, and personality characteristics. RESULTS Unemployment was associated with an increased risk of suicide and death from undetermined causes. Low education, personality characteristics, use of sleeping pills or tranquilizers, and serious or long-lasting illness tended to strengthen the association between unemployment and early mortality. CONCLUSIONS An increased risk of death from external causes implies a need for support for those experiencing unemployment, particularly susceptible individuals.

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 ≥0.2 μT, 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 ≥0.2 μT, 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.

Neurodegenerative diseases in welders and other workers exposed to high levels of magnetic fields.

Background Previous work has suggested an increase in risk of amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease among workers exposed to extremely low-frequency magnetic fields (ELF-MF). We evaluated the relation between ELF-MF from occupational exposures and mortality from neurodegenerative diseases. Methods The study was based on a cohort of Swedish engineering industry workers, comprising 537,692 men and 180,529 women. The cohort was matched against the 3 most recent censuses and The Causes of Death Registry. Levels of ELF-MF exposure were obtained by linking occupation according to the censuses to a job exposure matrix. We used 4 levels of exposure and considered both the primary and contributing causes of death, 1985-96. Results The risk of Alzheimer’s disease as primary or contributing cause of death increased with increasing exposure to ELF-MF among both men and women, with a relative risk (RR) of 4.0 and a 95% confidence interval (95% CI) of 1.4-11.7 in the highest exposure group for both sexes combined. There was a RR of 2.2 (95% CI: 1.0-4.7) for ALS in the highest exposure group with the suggestion of an exposure-response relationship. No evidence of increased risk was seen for Parkinson’s disease or multiple sclerosis. Conclusions The findings support previous observations of an increased risk of Alzheimer’s disease and ALS among employees occupationally exposed to ELF-MF. Further studies based on morbidity data are warranted.

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.

Incidence of selected cancers in Swedish railway workers, 1961–79

Among all Swedish men, 20 to 64 years of age and employed in 1960, railway workers were selected and compared with the population at large, concerning the incidence of leukemia, lymphoma, tumors of the brain, breast, and the pituitary gland. The study was a re-analysis of the 1961–79 incidence data previously showing no increase in risk for leukemia and brain tumors for railway workers. In the present study, follow-up was divided into two 10-year periods, and elevated relative risks (RR) were found for the first decade. For the first decade, engine drivers and conductors combined had an RR of chronic lymphocytic leukemia, acute myeloid leukemia, and lymphoma of 1.9 (95 percent confidence interval [CI]=0.9–4.0), 1.4 (CI=0.4–4.3), and 1.0 (CI=0.5–1.9), respectively. For all brain tumors, the RR was 1.2 (CI=0.8–1.9), with a higher risk estimate for those below age 30 (RR=12.2, CI=2.8–52.5). Three cases of breast cancer and nine cases of tumors of the pituitary gland occurred among engine drivers and conductors, corresponding to RRs of 4.9 (CI=1.6–11.8) and 3.2 (CI=1.6–6.2), respectively. Work on trains entails extremely high exposure to low frequency magnetic fields (EMF). The results give some support to the hypothesis of an association between EMF and certain types of cancers. The outcome for the pituitary gland, being a focal point of hormonal regulation, suggests a hormonal link.

Physical activity and risk for breast cancer a prospective cohort study among Swedish twins

The epidemiologic association between physical activity and breast cancer has been corroborated in many studies. Some inconsistencies remain, possibly due to variation in life periods for exposure assessment, confounding and undetected effect modification. In our cohort study, we address some of these questions by taking into account physical activity in different periods of life and by investigating effect modification by birth cohort and body mass index (BMI). Altogether 9,539 same‐sex twin women aged 42–70 years who answered a questionnaire about their work and leisure‐time physical exercise from ages 25 to 50 during 1967 and 1970 were included in our cohort. During follow‐up, 506 breast cancer cases occurred through 1997. We used multivariate Cox models to estimate relative risk (RR) with 95% confidence interval (CI). We found no associations between physical activity and breast cancer overall. Women born between 1901 and 1917 (aged 51–70 at baseline) who reported regular leisure‐time activity had a borderline significant 40% lower risk compared with those who reported no activity (RR 0.6; 95% CI 0.4–1.0; test for trend, p = 0.07). This association appeared to be confined to women with a low BMI after the age of 50 and to women with a high BMI during the premenopausal period. We found no evidence that work activity reduces risk for breast cancer. The importance of physical activity for breast cancer risk seems to depend on birth cohort. The association may be limited to normal‐weight postmenopausal women and overweight premenopausal women.

Malignant melanoma risk by nativity, place of residence at diagnosis, and age at migration

Although geographic latitude is clearly linked to the risk of cutaneous malignant melanoma, the chronology of this link is unclear. Based on the 4,611 cases of melanoma with known place of nativity diagnosed in 1972–82 among the non-Latino White residents of Los Angeles County (California, United States) of known place of origin, migrants to Los Angeles from higher US latitudes enjoy relative safety from skin melanoma. This relative safety is largely unaffected by the interval since migration, even after decades of residence in Los Angeles. The same relative protection is enjoyed by native residents of more northerly US communities in comparison with co-resident migrants from the southwestern US. While the observed effect of latitude is consistent with the accepted importance of solar radiation as a determinant of melanoma risk, it suggests that early, rather than late or cumulative, exposure is of most importance. This finding does not affirm the belief that protection of adult skin from exposure to the sun will reduce the risk from melanoma. It does suggest that decades must pass before it will be possible to assess the impact on melanoma risk of any increase in ultraviolet radiation delivered to the earth as a result of the destruction of atmospheric ozone.