Academic journal article Bulletin of the World Health Organization

Residential Exposure to Electromagnetic Fields and Childhood Leukaemia: A Meta-Analysis

Academic journal article Bulletin of the World Health Organization

Residential Exposure to Electromagnetic Fields and Childhood Leukaemia: A Meta-Analysis

Article excerpt

Voir page 913 le resume en francais. En la pagina 913 figura un resumen en espanol.

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 fields (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 approach for systematically combining the results of previous studies in order to arrive at conclusions that cannot be drawn from the results of any one study alone. Although it has been applied most often to combine the results of randomized trials, use of meta-analysis is not confined to the synthesis of information from experimental studies. A large number of studies that involve meta-analysis of nonexperimental data have been published in recent years, although such use of the technique is less accepted than it is in the analysis of data from clinical trials (5). Meta-analyses of observational epidemiological studies have also previously been carried out to examine the relationship between residential EMF exposure and childhood leukaemia (6-11). In general, such analyses have shown a significant increased risk of childhood leukaemia when residential exposure is assessed through the use of wiring configuration codes (a categorical exposure rating scheme based on wire size and distance from the residence), whereas the association with other related markers of exposure, such as proximity to power lines and calculated magnetic fields from power lines, appears less evident.

Several well-conducted epidemiological studies on the association between EMFs and childhood leukaemia were published after the above-mentioned meta-analyses appeared. The purpose of the present investigation was to reassess the risk of childhood leukaemia associated with residential EMF exposure in the light of these more recent publications. In so doing we hoped to be able to provide answers to the following questions.

* Could the association between wire codes and childhood leukaemia be confirmed?

* Is there an association between childhood leukaemia and other markers of residential EMF exposure?

* What is the overall quality of existing studies and is there a relationship between the quality of studies and the magnitude of risk?

* What recommendations can we make for further studies, if warranted?

Materials and methods

Identification of relevant studies

Studies pertaining to the relationship between EMFs and childhood leukaemia were identified using a MEDLINE search of the medical literature published in English over the period 1966-98. Copies of the relevant articles were obtained and reviewed to identify additional references.

To be eligible for inclusion in the meta-analyses, studies had to satisfy the following criteria: be primary studies, not reanalyses or reviews; be of case-control, cohort, or cross-sectional design; examine residential-based exposures through wiring configuration codes, distance to power distribution equipment, spot and 24-h measures of magnetic field strength (magnetic flux density), and calculated magnetic fields; examine childhood leukaemia; report an odds ratio and its variance or sufficient data to estimate them; be in English, and be published before January 1999.

Quality assessment

Each article was blinded with regard to authors, institution, and journal. The articles were read and scored for quality by two independent readers using a system that incorporates elements of methods developed by Chalmers et al. …

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