In a nested case-control study of 1,484 cancer cases and 2,179 matched controls from a cohort of 31,543 Ontario Hydro male employees, the authors evaluated associations of cancer risk with electric field exposure and reevaluated the previously reported findings for magnetic fields. Pensioners were followed from January 1, 1970, and active workers (including those who left the corporation) from January 1, 1973, with both groups followed through December 31, 1988. Exposures to electric and magnetic fields and to potential occupational confounders were estimated through job exposure matrices. Odds ratios were elevated for hematopoietic malignancies with cumulative electric field exposure. After adjustment, the odds ratio for leukemia in the upper tertile was 4.45 (95% confidence interval (CI) 1.01-19.7). Odds ratios were also elevated for acute nonlymphoid leukemia, acute myeloid leukemia, and chronic lymphoid leukemia. For cumulative magnetic field exposure, there were similar elevations that fell with adjustment. Evaluation of the combined effect of electric and magnetic fields for leukemia showed significant elevations of risk for high exposure to both, with a dose-response relation for increasing exposure to electric fields and an inconsistent effect for magnetic fields. There was some evidence of a nonsignificant association for brain cancer and benign brain tumors with magnetic fields. For lung cancer, the odds ratio for high exposure to electric and magnetic fields was 1.84 (95% CI 0.69-4.94).

A population‐based case‐control study was conducted in Ontario, Canada, to assess the relation between the risk of childhood leukemia and residential exposure to magnetic fields. Participating subjects consisted of 201 cases, diagnosed at 0 to 14 years of age during 1985–1993, ascertained from the records at the Hospital for Sick Children (Toronto), and 406 individually matched controls. Where possible, point‐in‐time measurements of magnetic fields were made in all residences occupied by subjects during the period of inquiry in the defined catchment area. Three different classification schemes of wire code were assigned to each residence. Detailed information was collected by interviewer‐administered questionnaires, which enabled risk estimates to be adjusted for socio‐economic characteristics, medical history of parent(s) and child and environmental exposures. Inconsistent elevations in risk were associated with time‐weighted averages of magnetic fields both inside and outside the home for subjects having residential point‐in‐time measurements that represented at least 70% of their etiological period. These risks increased in magnitude when analysis was restricted to children under 6 years of age at diagnosis or to those with acute lymphoblastic leukemia. For children younger than 6 years at diagnosis, outside perimeter measurements of the residence, ≥0.15 μT, were associated with increased leukemia risk (OR = 3.45, 95% CI = 1.14–10.45). Evaluation of different exposure times for point‐in‐time magnetic field measurements and wire configuration suggested that exposures earliest in the etiological period were associated with greater risks for children diagnosed at a younger age (OR = 2.50, 95% CI = 1.14–5.49). Our findings did not support an association between leukemia and proximity to power lines with high current configuration. Int. J. Cancer 82:161–170, 1999. © 1999 Wiley‐Liss, Inc.

A population-based case-control study was conducted in Ontario, Canada, to assess the relation between the risk of childhood leukemia and residential exposure to magnetic fields. Participating subjects consisted of 201 cases, diagnosed at 0 to 14 years of age during 1985-1993, ascertained from the records at the Hospital for Sick Children (Toronto), and 406 individually matched controls. Where possible, point-in-time measurements of magnetic fields were made in all residences occupied by subjects during the period of inquiry in the defined catchment area. Three different classification schemes of wire code were assigned to each residence. Detailed information was collected by interviewer-administered questionnaires, which enabled risk estimates to be adjusted for socio-economic characteristics, medical history of parent(s) and child and environmental exposures. Inconsistent elevations in risk were associated with time-weighted averages of magnetic fields both inside and outside the home for subjects having residential point-in-time measurements that represented at least 70% of their etiological period. These risks increased in magnitude when analysis was restricted to children under 6 years of age at diagnosis or to those with acute lymphoblastic leukemia. For children younger than 6 years at diagnosis, outside perimeter measurements of the residence, H0.15 T, were associated with increased leukemia risk (OR ‫؍‬ 3.45, 95% CI ‫؍‬ 1.14-10.45). Evaluation of different exposure times for point-in-time magnetic field measurements and wire configuration suggested that exposures earliest in the etiological period were associated with greater risks for children diagnosed at a younger age (OR ‫؍‬ 2.50, 95% CI ‫؍‬ 1.14-5.49). Our findings did not support an association between leukemia and proximity to power lines with high current configuration. Int. J. Cancer 82:161-170, 1999. Wiley-Liss, Inc.The known causes of leukemia in children are relatively few, and their contribution to the current incidence of this malignancy is thought to be small. Although rare, leukemia is the most common cancer in children and is regarded by some as increasing in incidence (Schmidt, 1998;Desch and Bleyer, 1994). Within the last 2 decades, the role of electric and magnetic field (EMF) exposure has increasingly become a part of the body of research examining the etiology of this childhood cancer. The first suggestion that EMFs from power lines might cause cancer in children was made by Wertheimer and Leeper (1979). Extensive research since then has not resolved the question of whether EMFs increase the risk of cancer. While not all studies have shown increased risk estimates, there has been some consistency of positive findings relating to studies of children, specifically those with leukemia, and EMF exposure as defined by wiring of high current configuration. Wire configuration is an indirect measure of personal exposure; therefore, the extent to which it is an accurate index of exposure, particularly long-term exposure, remains unknown. Mo...

The findings relating to magnetic field exposures directly measured by personal monitoring support an association with the risk of childhood leukemia. As exposure assessment is refined, the possible role of magnetic fields in the etiology of childhood leukemia becomes more evident.

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