BMJ  2005;331:635 (17 September), doi:10.1136/bmj.331.7517.635-a

Letter

Childhood cancer and power lines

Study had important omissions

Editor—The study by Draper et al omitted most cases near power lines of 132 kV.¹ The United Kingdom has 10 000 circuit km of 400 kV lines and 4000 circuit km of 275 kV lines, but 20 000 circuit km of 132 kV lines and more than 260 000 pole mounted transformers.² Should the effect be found near these lower voltage sources, then saying that only five cases per year would result becomes a dramatic understatement. Major residential exposure to electromagnetic fields is not from power lines but from home appliances and wiring, and these could also augment incidence.

At 50 Hz no association exists between strengths of electromagnetic fields since people who are exposed are in the source's near field. Magnetic fields from power lines will attenuate at 1/r³, whereas electric fields may attenuate only at the simple reciprocal, thereby still exceeding average levels much further away, accelerated or diminished by metal objects or screening.

Draper et al therefore argue for involvement of electric fields. Henshaw's hypothesis implicating corona discharges cannot be a complete answer since these are unlikely from 50 Hz domestic sources.³ Our 1996 study found a 4.7-fold incidence of childhood leukaemia when the electric component was on average 20 V/m, with power lines only a minor exposure source.⁴

The UK childhood cancer study also measured bedplace electric fields, finding mildly raised incidences, but reported only spot measurements and 48 hour measurements—neither representing children's nocturnal exposure.⁵ Were the study's data reanalysed to reflect only night-time exposure the incidence might be found to be similarly high to ours.

If electric fields are bioactive (and most epidemiological research has been directed only to the magnetic component) then a biological mechanism becomes more plausible, since electric fields are superpositive. Many studies of important life processes (heart beat rate, electroencephalogram, ATP synthesis) are mediated via electric currents. Their fields, or electron transport, report adverse effects from exposure to electromagnetic fields. In vitro studies and animal studies also report adverse electric field effects, particularly on lymphocytes and on melatonin synthesis. The supplementary use of melatonin is proving a useful adjuvant as a radioprotective agent, not only at power but also at radiofrequencies.^w1

Coghill Research Laboratories, Lower Race, Pontypool NP4 5UH roger{at}cogreslab.co.uk

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Competing interests: None declared.

Reference w1 is available on bmj.com

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. Electricity Council. Statistics of electricity supply. London: Millbank, 1987.
3. Henshaw DL, Ross AN, Fews AP, Preece AW. Enhanced deposition of radon daughter nuclei in the vicinity of power frequency electromagnetic fields. Intl J Radiat Biol 1996;69: 25-38
4. Coghill RW, Steward J, Philips A. Extra low frequency electric and magnetic fields measured in the bedplaces of children diagnosed with leukaemia: a case control study. Europ J Cancer Prev 1996;5: 153-8.
5. Skinner J, Mee TJ, Blackwell RP, Maslanyj MP, Simpson J, Allen SG, et al. Exposure to power frequency electric fields and the risk of childhood cancer in the UK. Br J Cancer 2002;87: 1257-66.[Medline]

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