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

Letter

Childhood cancer and power lines

What do the data mean?

Editor—Draper et al used distance of mother's home from high voltage overhead transmission lines (predominantly 275 kV and 400 kV) at the time of her child's birth as a proxy for her child's subsequent exposure to power-frequency magnetic fields (reviewed by Ahlbom et al).^{1 2} As they acknowledge, this is a crude estimate since, in contrast to other reports,² no household measurements were taken, no data on more prevalent low voltage distribution sources were collected, no information from other time points in the child's life was obtained, variations during the 33 years period studied were not considered, and no validatory home visits were carried out. A recent report into residential exposures to magnetic fields in the United Kingdom estimated that proximity to high voltage lines, 275 kV and above, explained only 9% of those with measurements 0.2 microtesla (µT).³

National data on the distribution of houses in relation to high voltage lines in the UK were provided (J Swanson, National Grid Transco, personal communication, 2000) to the UK Childhood Cancer Study (UKCCS) Group for its study of power lines and childhood cancer, to assess the representativeness of study subjects.⁴ An equivalent comparison using National Grid data spanning the far longer period investigated in the paper by Draper et al was not undertaken. The assessments of distance to power lines in the UKCCS were made for all registered controls, who have been shown to represent the general population.⁵

View larger version (35K): [in this window] [in a new window]   Study by Draper et al—proportion of subjects living close to power lines. Comparison with national data supplied by National Grid Transco (NGT) and UK childhood cancer study (UKCCS)

 

A plot of the distributions of the leukaemia and non-leukaemia cases and controls in the study by Draper et al, national populations, and UKCCS populations by distance from high voltage lines (figure) seems to show that the leukaemia controls used in the analysis presented by Draper et al are systematically different. Their positive result over 100 m may therefore be explained not by an excess of cases but by a deficit of controls in the early years of the study.

Institute of Public Health, Strangeways Research Laboratory, Cambridge CB1 8RN nick.day{at}srl.cam.ac.uk

Academic Unit of Paediatric Oncology, Christie Hospital and Central Manchester and Manchester Children's University Hospitals NHS Trusts, Manchester M20 4BX

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

Epidemiology and Genetics Unit, Department of Health Sciences, University of York, York YO10 5DD

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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: a case-control study. BMJ 2005;330: 1290. (4 June.)[Abstract/Free Full Text]
2. Ahlbom A, Day N, Feychting M, Roman E, Skinner J, Dockerty J, et al. A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer 2000;83: 692-8.[CrossRef][ISI][Medline]
3. Maslanyj MP, Mee TJ, Allen SG, Investigation and identification of sources of residential magnetic field exposures in the United Kingdom childhood cancer study (UKCCS). www.hpa.org.uk/radiation/publications/hpa_rpd_reports/2005/hpa_rpd_005.htm (accessed 28 Aug 2005).
4. Skinner J, Maslanyj M, Mee TJ, Allen SG, Simpson J, Roman E, et al. Childhood cancer and residential proximity to power lines. UK Childhood Cancer Study Investigators. Br J Cancer 2000;83: 1573-80.[CrossRef][ISI][Medline]
5. UK Childhood Cancer Study Investigators. The United Kingdom childhood cancer study: objectives, materials and methods. Br J Cancer 2000;82: 1073-102.[CrossRef][ISI][Medline]

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Relevant 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]