Do power frequency magnetic fields cause leukemia in children?

The possibility of a causal relationship between exposure to electromagnetic fields and childhood leukemia has been studied for more than 10 years. This review evaluates the epidemiologic findings relevant to a possible causal association between exposure to power frequency magnetic fields during childhood and leukemia. The nine published studies on this topic were analyzed, with a focus on the selection of subjects, assessment of exposure, and control of confounding. Consistency of a positive association and dose-response relationship are evident for assessment of past exposure: among the five recent studies, relative risk estimates vary from 1.5 to 2.7 for past exposure assessment, and a significant dose-response relation was found in three studies. These observations cannot be explained by misclassification of exposure or consistent selection bias, and a confounder effect could hardly explain such results. Even if there is no currently understood biological plausibility for such an association, its possible causal nature cannot be dismissed. The impact on public health of such a possible causal association is difficult to assess precisely but could be significant. Therefore, it might be prudent to consider interim preventive measures while we await results of further research.