BMJ  2005;331:634-635 (17 September), doi:10.1136/bmj.331.7517.634-a

Letter

Childhood cancer and power lines

Results do not support causal role for electromagnetic fields

Editor—Draper et al present findings on the relation between childhood cancer and the distance of birth residence to high voltage power lines.¹ The study's strengths include the large number of case children and unbiased control selection. However, the findings are inconsistent with another UK study, in which neither proximity nor estimates of dose to extremely low frequency magnetic fields from power lines showed any relation with childhood leukaemia.²

The strength of the findings is based on trend statistics, with the reference group resident over 600 m from the lines. This has no sound scientific basis for inferring associations with extremely low frequency magnetic fields, as beyond 200 m their contribution to exposure can be considered to be "background."³ No plausible biological evidence currently links magnetic field exposure to childhood leukaemia. Despite this, the paper quantifies the likely number of cases "associated" with high voltage lines where the main exposure is to magnetic fields.

The significant associations in this geographical analysis lack any adjustment for population characteristics except social class, and how this was done for births before the 1981 census is not described. Crucially, the area distribution of childhood leukaemia varies with population density and population mixing⁴; neither has been considered as potential confounders.

It is of interest that using all controls as the comparison group reduced the risk. Matched analyses may be preferred, but findings can be considered less conclusive if the estimates are noticeably different when matching is broken. All controls were selected to represent the population, and an investigation of why differences were observed is warranted.

The findings of this study point towards geographical correlates of risk for childhood leukaemia but do not support the hypothesis that electromagnetic fields have a causal role.

s.j.hepworth{at}leeds.ac.uk

Paediatric Epidemiology Group, University of Leeds, Leeds LS2 9LN

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Competing interests: None declared.

References

1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: case-control study. BMJ 2005; 330: 1290-2. (4 June.)[Abstract/Free Full Text]
2. UK Childhood Cancer Study Investigators. Childhood cancer and residential proximity to power lines. Br J Cancer 2000;83: 1573-80.[CrossRef][ISI][Medline]
3. Vistnes AI, Ramberg GB, Bjørnevik LR, Tynes T, Haldorsen T. Exposure of children to residential magnetic fields in Norway: is proximity to power lines an adequate predictor of exposure? Bioelectromagnetics 1997;18: 47-57.[CrossRef][ISI][Medline]
4. Parslow RC, Law GR, Feltbower R, Kinsey SE, McKinney PA. Population mixing, childhood leukaemia, CNS tumours and other childhood cancers in Yorkshire. Eur J Cancer 2002;38: 2033-40.

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Related Article

Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study

Gerald Draper, Tim Vincent, Mary E Kroll, and John Swanson
BMJ 2005 330: 1290. [Abstract] [Full Text] [PDF]