The UKCCS

Lancet 1999 Dec 4;354(9194):1925-31
Exposure to power-frequency magnetic fields and the risk of childhood cancer.

UK Childhood Cancer Study Investigators.

BACKGROUND: Previous studies have suggested an association between exposure to power-frequency electromagnetic fields (EMF) and the development of childhood malignant disease, especially leukaemia and tumours of the central nervous system. We investigated the relation between all childhood cancer and exposure to power-frequency magnetic fields. METHODS: The UK Childhood Cancer Study was a population case-control study covering the whole of England, Wales, and Scotland. All children with a confirmed malignant disorder were potentially eligible. For each case, we matched two controls on date of birth and sex, randomly chosen from the list of the Family Health Services Authority in England and Wales or Health Board in Scotland. In the main study, 3838 cases and 7629 controls were interviewed. The EMF part of the study included only one control per case, and household EMF measurements and school measurements where relevant were taken on 2226 matched pairs. These measurements, adjusted for historical line load and appliance fields, were used to estimate average exposure in the year before the date of diagnosis, or an equivalent date for controls. Analyses were by conditional logistic regression, incorporating a census-derived deprivation index used as a measure of socioeconomic status. FINDINGS: For children with mean exposures of more than 0.2 microT compared with children with mean exposures of less than 0-1 microT, the adjusted odds ratios were 0.92 (95% CI 0.47-1.79) for acute lymphoblastic leukaemia, 0.90 (0.49-1.63) for all leukaemia, 0.46 (0.11-1.86) for central-nervous-system tumours, 0.97 (0.46-2.05) for other malignant disease, and 0.87 (0.56-1.35) for all malignant disease combined. Higher exposures (>0.4 microT) were recorded for only 17 (<0.4%) individuals (eight cases, nine controls). INTERPRETATION: This study provides no evidence that exposure to magnetic fields associated with the electricity supply in the UK increases risks for childhood leukaemia, cancers of the central nervous system, or any other childhood cancer.

Link between electromagnetic fields and childhood cancer unresolved
Commentary in the Lancet December 4 1999

The long-awaited UK Childhood Cancer Study (UKCCS) on exposure to power-frequency magnetic fields and risk of childhood cancer published in today's Lancet does not support the hypothesis that exposure to magnetic fields, associated with the use or transmission of electricity in the UK, increases the risk of childhood leukaemia, central nervous system tumours, or any other childhood cancer.
Reviews of epidemiological studies conducted by the US National Research Council,1 WHO,2 and the National Institute of Environmental Health Sciences (NIEHS)3 have suggested that there is a weak link between exposure to power-frequency magnetic fields and childhood leukaemia, with an odds ratio of about 1·5. Using the International Agency for Research on Cancer criteria for classifying potential carcinogens, an international working group convened by the NIEHS3 rated exposure to power-frequency fields as a category 2B, a possible human carcinogen.
WHO, through its International EMF Project, has been promoting research that attempts to address this 2B classification. From WHO's viewpoint, although the UKCCS is very large and well conducted, it is not the "definitive" study many scientists have been hoping for.
The first reason is that this study was designed many years ago, so the exposure assessment relies on time-weighted average (TWA) fields. TWA has been used in many studies but does not relate to any known mechanism of action of low-frequency fields in tissues. A recent WHO report4 recommends that, although TWA should continue to be used in future epidemiological studies for comparison purposes, other measures that relate to known mechanisms should also be included in the exposure-assessment protocol. Key among these measures is an assessment of any rapid changes in the magnetic field (transients) that occur when appliances are used, and in transients from distribution lines. Currents induced by power transients can produce signals in cells above the cell's normal electrical-noise levels.5
The second reason why the study is not definitive is the low numbers of children in the higher exposure categories. As the UKCCS investigators state, only 2·3% of their controls had been exposed to magnetic fields over 0·2 µT. Although this percentage is similar to that in Germany (2%),6 in the US study7 it was 11·4% and in the Canadian study8 15·4%. This difference reflects, in part, the line voltage in North America of about 110 V, and in Europe of 220 V. Thus for the same power consumption North Americans use twice as much current as Europeans do, and so are exposed to about double the magnetic-field strength. Another factor influencing the level of magnetic-field exposure between the two continents relates to how the power is distributed--for example, how electrical wiring is configured in homes and how the currents are earthed. Whatever the explanation, the small numbers in the higher exposure categories mean that the UKCCS provide evidence only for exposures of up to 0·2 µT.
The third reason is that the small numbers of cases and controls in the higher exposure categories are unlikely to significantly affect the results of previous meta-analyses and reviews suggesting a weak link between power-frequency magnetic-field exposure and childhood leukaemia.1­3 An analysis, funded by the European Union, which includes the UKCCS, is near completion.
Today's Lancet also carries a research letter reporting some new data from a previously published New Zealand study.9 However, the study has the same inadequacies as the UKCCS.
A major childhood leukaemia study is being done by Japan's National Institute of Environmental Studies. This study will take account of transients in the assessment of exposure to magnetic fields. 1500 cases (1000 leukaemia and 500 brain tumours) and a similar number of matching controls will be recruited. Because Japan is highly industrialised, the study is expected to have large numbers in the high-exposure groups. This study, in conjunction with those being done in Germany and Italy, may be one of the last hopes of finally resolving the vexing issue of whether there is truly an increased risk of childhood cancer from exposure to magnetic fields or whether the weak association is occurring by chance. *Michael H Repacholi, Anders Ahlbom *Division of Occupational and Environmental Health, World Health Organization, CH-1211, Geneva 27, Switzerland; and National Institute of Environmental Medicine, Karolinska Institutet, Sweden

Br J Cancer 2000 Dec;83(11):1573-80
Childhood cancer and residential proximity to power lines.

UK Childhood Cancer Study Investigators.

In the United Kingdom Childhood Cancer Study, a population-based case-control study covering the whole of England, Scotland and Wales, measured power-frequency magnetic fields were not found to be associated with risk for any malignancy. To examine further the risk associated with residential proximity to electricity supply equipment, distances to high-voltage lines, underground cables, substations and distribution circuits were collected for 3380 cases and 3390 controls. Magnetic field exposure from this equipment was calculated using distance, load and other circuit information. There was no evidence that either proximity to electrical installations or the magnetic field levels they produce in the UK is associated with increased risk of childhood leukaemia or any other cancer. Odds ratios of 0.73 (95% CI = 0.42-1.26) for acute lymphoblastic leukaemia, 0.75 (95% CI = 0.45-1.25) for all leukaemias, 1.08 (95% CI = 0.56-2.09) for central nervous system cancers and 0.92 (95% CI = 0.64-1.34) for all malignancies were obtained for residence within 50 m of an overhead line. When individuals with a calculated magnetic field exposure > or = 0.2 microT were compared to those in a reference category of exposure <0.1 microT, odds ratios of 0.51 (95% CI = 0.11-2.33) for acute lymphoblastic leukaemia, 0.41 (95% CI = 0. 09-1.87) for total leukaemia, 0.48 (95% CI =0.06-3.76) for central nervous system cancers and 0.62 (95% CI = 0.24-1.61) for all malignancies were obtained. Copyright 2000 Cancer Research Campaign.

Br J Cancer 2002 Nov 18;87(11):1257-66
Exposure to power frequency electric fields and the risk of childhood cancer in the UK.

Skinner J, Mee TJ, Blackwell RP, Maslanyj MP, Simpson J, Allen SG, Day NE, Cheng KK, Gilman E, Williams D, Cartwright R, Craft A, Birch JM, Eden OB, McKinney PA, Deacon J, Peto J, Beral V, Roman E, Elwood P, Alexander FE, Mott M, Chilvers CE, Muir K, Doll R, Taylor CM, Greaves M, Goodhead D, Fry FA, Adams G, Law G; United Kingdom Childhood Cancer Study Investigators.

Strangeways Research Laboratory, University of Cambridge, Wort's Causeway, Cambridge CB1 8RN, UK.

The United Kingdom Childhood Cancer Study, a population-based case-control study covering the whole of Great Britain, incorporated a pilot study measuring electric fields. Measurements were made in the homes of 473 children who were diagnosed with a malignant neoplasm between 1992 and 1996 and who were aged 0-14 at diagnosis, together with 453 controls matched on age, sex and geographical location. Exposure assessments comprised resultant spot measurements in the child's bedroom and the family living-room. Temporal stability of bedroom fields was investigated through continuous logging of the 48-h vertical component at the child's bedside supported by repeat spot measurements. The principal exposure metric used was the mean of the pillow and bed centre measurements. For the 273 cases and 276 controls with fully validated measures, comparing those with a measured electric field exposure >/=20 V m(-1) to those in a reference category of exposure <10 V m(-1), odds ratios of 1.31 (95% confidence interval 0.68-2.54) for acute lymphoblastic leukaemia, 1.32 (95% confidence interval 0.73-2.39) for total leukaemia, 2.12 (95% confidence interval 0.78-5.78) for central nervous system cancers and 1.26 (95% confidence interval 0.77-2.07) for all malignancies were obtained. When considering the 426 cases and 419 controls with no invalid measures, the corresponding odds ratios were 0.86 (95% confidence interval 0.49-1.51) for acute lymphoblastic leukaemia, 0.93 (95% confidence interval 0.56-1.54) for total leukaemia, 1.43 (95% confidence interval 0.68-3.02) for central nervous system cancers and 0.90 (95% confidence interval 0.59-1.35) for all malignancies. With exposure modelled as a continuous variable, odds ratios for an increase in the principal metric of 10 V m(-1) were close to unity for all disease categories, never differing significantly from one.