The Childhood Cancer Research Group at the University of Oxford conducted a study on cancer rates in relation to power lines. The study is sometimes called the "CCRG" study or sometimes the "Draper" study after Dr Gerald Draper, the Director of the CCRG (now retired) and the lead author of the first publication. The first paper was published in 2005 and the final planned paper in 2016.
The study has produced a sequence of papers which we summarise here with more details on separate pages for the key results papers. See also the abstracts of these papers. A parallel study by Imperial College has looked at adult cancers.
The distance results paper
This paper was published in the British Medical Journal on 3 June 2005 and gave results for distance from 275 kV and 400 kV power lines in England and Wales.
- full details
- the abstract from the study
- the complete study on the BMJ web site
- responses by other organisations to this study
The results in a nutshell
- Children who lived within 200 m of high-voltage power lines 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.
- The results do not seem to be compatible with the existing data on magnetic fields and cancer because they extend too far from the line. This was explored more fully in the subsequent magnetic-fields paper.
- There is no evidence the results are explained by the “corona ion” hypothesis
Note: the later "follow on" paper found that this risk had diminished over the years
This paper, published in the Annals of the New York Academy of Sciences in 2006, reviewed the state of EMF epidemiology with particular reference to how the CCRG distance results relate to existing findings.
see the abstract
This paper, published in the Journal of Radiological Protection in 2008, gave full details of the exposure-assessment methods used in the distance and magnetic fields papers.
see the abstract
The magnetic-fields results paper
This paper, published in the British Journal of Cancer in 2010, looks at exactly the same subjects (and power lines) as the "distance" paper, but instead of just calculating the distance from the power line, goes further and calculates the magnetic field from the power line.
Results in a nutshell
For childhood leukaemia, there is a relative risk for fields greater than 0.4 µT compared to fields less than 0.1 µT of about 2, which is not statistically significant in itself but is consistent with previous studies. But these magnetic fields are found only really within 50 m or so of these power lines. Therefore magnetic fields seem extremely unlikely to explain the previous "distance" findings, where the elevation in risk extended at least 600 m.
A 2012 paper (see full abstract) looked at the father's occupation, as recorded on the birth certificate, and the subsequent risk of the child getting leukaemia. Among various findings relating to social class, social contacts, etc, there was a raised risk in the "other" group of leukaemias (that is, not lymphoid or acute myeloid) for occupations deemed to involve EMF exposure. The authors suggest this could be a chance finding, as they looked at 33 exposures and you would expect some of those to be positive and some negative by chance alone.
The follow-on paper
A 2014 paper extended the original 2005 result to include 132 kV power lines, cases in Scotland, larger distances from the power lines, and cases from more recent years up to 2008.
Results in a nutshell
In terms of the elevated rates for childhood leukaemia, Scotland seems to be consistent with England and Wales, and 132 kV lines similar to 275 and 400 kV lines (but producing a lesser elevated risk), The elevation doesn't seem to extend beyond the original 600 m. But the elevation in leukaemia rates is now found to have diminished over the decades from the 1960s to the present.
Methodology supplement - accuracy of grid references
In October 2014, the CCRG published a short Note giving some extra analysis on methodology. Specifically, they looked at the relative accuracy of grid references derived from postcodes as compared to the actual address. The conclusion is, broadly, that postcodes may be good enough if you are just interested in general effects in the proximity of a power line, but if you want to be accurate enough to look at magnetic-field effects, you need the actual address not the postcode.
The corona ions paper
In October 2014 CCRG published a paper looking at whether their results could be explained by the "corona ion hypothesis". This theory suggests that the air ions produced on the surface of the conductors of high-voltage power lines are blown away by the wind, attach to existing airborne pollutants making those pollutants more charged, which in turn makes them more likely to be retained in the airways when breathed in and increase any health effects they already cause.
CCRG modelled this effect, using actual meteorological data to look at the wind directions, and concluded:
Thus, we conclude that the simple corona-ion hypothesis that we test here explains the observed pattern of leukaemia rates around power lines less well than straightforward distance. Our findings therefore do not support this corona-ion hypothesis as the explanation of these results.
The underground cables paper
In 2015 the CCRG published a paper on underground cables. The point of this is that underground cables produce magnetic fields, but (unlike overhead lines) nothing else and are visually prominent, so if there was an association with underground cables, it would almost have to be caused by magnetic fields.
In fact, the study did not find associations:
We have, in fact, overall found no evidence of increased risks for leukaemia. Despite the tiny fraction of people living close to UGCs, which severely limits the statistical power, the large overall size of this study means that this finding still carries some weight ..... We conclude that these results are modest, though far from conclusive, evidence against MFs being a cause of leukaemia, and therefore, indirectly, provide some further suggestive evidence that where risk elevations are found near OHLs, they may be caused by factors other than MFs.
This paper published in 2016 is the final paper planned from this project and reports a number of subanalyses - subtypes of leukaemia, ages of child, etc - that didn't get included in any of the previous papers. None of the results are particularly striking but they all add to the overall picture.
The future of the CCRG
The CCRG closed in 2014. The Registry moved to a different part of the University of Oxford, but the related research activity ceased. The key staff continued working on this particular study on a voluntary basis, so the final analyses were still completed.