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Although individual epidemiological investigations have suggested associations between residential exposure to electromagnetic fields (EMFs) and childhood leukaemia, overall the findings have been inconclusive. Several of these studies do, however, lend themselves to application of the meta-analysis technique. For this purpose we carried out searches using MEDLINE and other sources, and 14 case-control studies and one cohort study were identified and evaluated for epidemiological quality and included in the meta-analysis. Relative risk estimates were extracted from each of the studies and pooled. Separate meta-analyses were performed on the basis of the assessed EMF exposure (wiring configuration codes, distance to power distribution equipment, spot and 24-h measures of magnetic field strength (magnetic flux density) and calculated magnetic field). The meta-analysis based on wiring configuration codes yielded a pooled relative risk estimate of 1.46 (95% confidence interval (CI) = 1.05-2.04, P= 0.024) and for that for exposure to 24-h measurements of magnetic fields, 1.59 (95% Cl = 1.14-2.22, P= 0.006), indicating a potential effect of residential EMF exposure on childhood leukaemia. In most cases, lower risk estimates were obtained by pooling high-quality studies than pooling low-quality studies. There appears to bea clear trend for more recent studies to be of higher quality. Enough evidence exists to conclude that dismissing concerns about residential EMFs and childhood leukaemia is unwarranted. Additional high-quality epidemiological studies incorporating comparable measures for both exposure and outcomes are, however, needed to confirm these findings and, should they prove to be true, the case options for minimizing exposure should be thoroughly investigated to provide definitive answers for policy-makers.
Keywords: electromagnetic fields; leukaemia, radiation induced; meta-analysis; risk factors.
Introduction
In 1979 Wertheimer & Leeper (1) published the first report that showed an increased risk of cancer mortality among children living near electrical wiring configurations and which were consistent with the presence of high currents. Although many studies linking exposure to electromagnetic field, (EMFs) with health effects have been conducted, there is still much debate over whether this exposure at the levels that occur in domestic settings can cause cancer, particularly childhood leukaemia. Some workers have recently called for an end to further research on exposure to magnetic fields (2), whereas others believe that abandoning research on this topic is premature (3, 4).
Meta-analysis is a quantitative...