The authors respond:
The letters from de Vocht1 and Philips et al2 both note that, in our national study of adult cancer risk and high-voltage power lines,3 point estimates >1.0 were observed in close proximity to power lines for the risk of leukemia and of brain and central nervous system (CNS) tumors, even though confidence intervals were wide. Philips et al2 reaggregate the distance cutoffs shown in our figures and tables and, after adjustment for potential confounders, report an association (P = 0.03) for a one-sided test for leukemia within 100 m of a power line.
In a study of childhood cancers in Great Britain based on the National Grid power line data, Draper et al4 found an excess of childhood leukemia that extended up to 600 m of a power line. However, the pattern of excess risks did not match magnetic field estimates, leading the authors to question a causal association with magnetic fields as an explanation for their findings. Similarly, we give greater weight to our findings on magnetic fields than to our findings regarding distance from power lines, especially in view of evidence in our article of potential confounding between distance and socioeconomic factors.
Unlike in other studies, we were able to examine risks associated with magnetic field estimates up to 1000 nT or more. As noted in our report, there were no meaningful excess risks observed for leukemia and brain/CNS cancers with or without adjustment for potential confounders, and no trend of risk with increasing magnetic fields. Our findings do not support an epidemiologic association between magnetic fields and risk of adult cancers.
Mireille B. Toledano
Small Area Health Statistics Unit
MRC-HPA Centre for Environment and Health
School of Public Health
Imperial College London
St Mary’s Campus
London, United Kingdom
1. de Vocht F. Adult cancers near high-voltage power lines [letter]. Epidemiology. 2013;24:782
2. Philips A, O’Carroll M, Henshaw D, Lamburn G. Adult cancers near high-voltage power lines [letter]. Epidemiology. 2013;24:782–783
3. Elliott P, Shaddick G, Douglass M, de Hoogh K, Briggs DJ, Toledano MB. Adult cancers near high-voltage overhead power lines. Epidemiology. 2013;24:184–190
4. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study. BMJ. 2005;330:1290