A case-control study of childhood leukemia in Southern Ontario, Canada, and exposure to magnetic fields in residences

Abstract

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.

Exposure to power frequency electric fields and the risk of childhood cancer in the UK

“…A study from New Zealand (Dockerty et al, 1998) found no significant increase in risk using as exposure metrics the means of two 24-h measurements made in the centre of the most used room and by the child's bed. Two recent Canadian studies (McBride et al, 1999;Green et al, 1999) found no increase in risk using 48-h personal monitoring. The influence of the body on the electric field during personal monitoring, together with the possibility that case children may have changed their behaviour since developing the disease make these results hard to interpret.…”

Review of the Epidemiologic Literature on EMF and Health

“…Initial studies characterized field levels using short-term, or "spot," measurements taken immediately outside (23) or within residences (12), the latter obtained in the child's and parents' bedrooms. Subsequently, 24-hr measurements were obtained in rooms in which subjects spent a substantial proportion of time, based on interview data (9,15,19,21,(33)(34)(35)(36)(37). Such measurements are made after diagnosis, but unlike measurements based only on power lines, these inhome measurements reflect all sources of magnetic fields in the residence (38).…”

“…In residential studies assessing exposure using spot and/or 24-hr or longer area magnetic field measurements, increases in leukemia, ranging from 1.3-to 1.5-fold elevated, were reported for children with average magnetic field exposures ≥0.2 µT in Denver (based on 3 cases) (12), Los Angeles (based on 20 cases with exposures ≥0.268 µT) (15), Lower Saxony and Berlin, Germany (based on 4 cases) (33,34), nine Midwestern and mid-Atlantic states in the United States (based on 58 cases) (21), five provinces in Canada (based on 54 cases) (9), and the United Kingdom (based on 21 cases) (including England, Wales, and Scotland) (37). A 3.3-fold increase (95% confidence interval [CI] = 0.5-23.7) of leukemia was linked with 24-hr children's bedroom timeweighted average measurements ≥0.2 µT in a study in New Zealand (based on 5 cases) (34,79), and an odds ratio of 1.1 (95% CI = 0.31-4.06) was linked with point-in-time measurements ≥0.13 µT taken in the child's bedroom in a study in southern Ontario, Canada (based on 21 cases) ( Table 1) (36). The latest study is from Germany and showed a relative risk of 1.6 (0.7-3.7) for 0.2 µT and 3.2 (1.3-7.8) for nighttime exposure (80).…”

Description of a new computer wire coding method and its application to evaluate potential control selection bias in the Savitz et al. childhood cancer study

“…Other studies in both the United States and Canada did not ®nd associations between wire codes and childhood cancers [including Linet et al, 1997;McBride et al, 1999;Green et al, 1999]. The results from London et al fueled the debate about control selection bias.…”