The CCRG (or "Draper") study


Abstract

Objective
To determine whether there is an association between distance of home address at birth from high voltage power lines and the incidence of leukaemia and other cancers in children in England and Wales.

Design
Case-control study.

Setting
Cancer registry and National Grid records.

Participants
29081 children with cancer, including 9700 with leukaemia. Children were aged 0-14 years and born in England and Wales, 1962-95. Controls were individually matched for sex, approximate date of birth, and birth registration district. No active participation by cases or controls was required.

Main outcome measures
Distance from home address at birth to the nearest high voltage overhead power line in existence at the time. Results Compared with those who lived >600 m from a line at birth, children who lived within 200 m had a relative risk of leukaemia of 1.69 (95% confidence interval 1.13 to 2.53); those born between 200 and 600 m had a relative risk of 1.23 (1.02 to 1.49). There was a significant (P<0.01) trend in risk in relation to the reciprocal of distance from the line. No excess risk in relation to proximity to lines was found for other childhood cancers.

Conclusions
There is an association between childhood leukaemia and proximity of home address at birth to high voltage power lines, and the apparent risk extends to a greater distance than would have been expected from previous studies. About 4% of children in England and Wales live within 600 m of high voltage lines at birth. If the association is causal, about 1% of childhood leukaemia in England and Wales would be attributable to these lines, though this estimate has considerable statistical uncertainty. There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.



Ann N Y Acad Sci. 2006 Sep;1076:318-30
Power-frequency electric and magnetic fields in the light of Draper et al. 2005.

Swanson J, Vincent T, Kroll M, Draper G.

National Grid, London, WC2N 5EH, UK. john.swanson@physics.org

Power-frequency electric and magnetic fields are produced wherever electricity is used; exposure is ubiquitous. Epidemiologic studies find an association between children living in homes with the highest magnetic fields and childhood leukemia, but bias is a possible alternative to a causal explanation. A new study, Draper et al., looks at residence close to high-voltage power lines, one source of exposure to such fields, and its design avoids any obvious bias. It finds elevated childhood leukemia rates, but extending too far from the power lines to be straightforwardly compatible with the existing literature. This leads to an examination of alternative explanations: magnetic fields, other physical factors, such as corona ions, the characteristics of the areas power lines pass through, bias, and chance. The conclusion is that there is currently no single preferred explanation, but that this is a serious body of science that needs further work until an explanation is found.



J Radiol Prot. 2008 Mar;28(1):45-59. Epub 2008 Feb 26.
Methods used to calculate exposures in two epidemiological studies of power lines in the UK.

Swanson J.

Two epidemiological studies of cancer (one for children and one for adults) and proximity to high-voltage power lines are being performed in the UK. We describe the methods used to calculate exposure to magnetic fields in these studies. We used grid references derived from addresses for subjects and compared these to the grid references of pylons to calculate distances to power lines. We gathered relevant data on the power lines and used these to calculate magnetic fields. This required information on loads in the years from 1962 to the present. The only such information now available is a prediction of loads made for each year in advance, and the use of predictions rather than actual loads is the biggest source of error in these calculations. For a recent year, we compare the loads used in these studies with actual loads to assess the accuracy of our calculations. These calculations were performed by industry, and we describe the steps taken to ensure their trustworthiness, including conducting them all blind to the case-control status of the subjects.

British Journal of Cancer (2010) 103, 1122 – 1127
Childhood cancer and magnetic fields from high-voltage power lines in England and Wales: a case–control study

ME Kroll1, J Swanson2, TJ Vincent1 and GJ Draper1
1University of Oxford, Childhood Cancer Research Group, Richards Building, Old Road Campus, Headington, Oxford OX3 7LG, UK; 2National Grid, 1-3 Strand, London WC2N 5EH, UK

BACKGROUND: Epidemiological evidence suggests chronic low-intensity extremely low-frequency magnetic-field exposure is associated with increased risk of childhood leukaemia; it is not certain the association is causal.
METHODS: We report a national case–control study relating childhood cancer risk to the average magnetic field from high-voltage overhead power lines at the child’s home address at birth during the year of birth, estimated using National Grid records. From the National Registry of Childhood Tumours, we obtained records of 28 968 children born in England and Wales during 1962–1995 and diagnosed in Britain under age 15. We selected controls from birth registers, matching individually by sex, period of birth, and birth registration district. No participation by cases or controls was required.
RESULTS: The estimated relative risk for each 0.2 mT increase in magnetic field was 1.14 (95% confidence interval 0.57 to 2.32) for leukaemia, 0.80 (0.43–1.51) for CNS/brain tumours, and 1.34 (0.84–2.15) for other cancers.
CONCLUSION: Although not statistically significant, the estimate for childhood leukaemia resembles results of comparable studies. Assuming causality, the estimated attributable risk is below one case per year. Magnetic-field exposure during the year of birth is unlikely to be the whole cause of the association with distance from overhead power lines previously reported from this study.