The most notable study on childhood leukaemia and proximity to overhead lines carried out in the UK was by the Childhood Cancer Research Group (CCRG) at the University of Oxford. This study published several papers between 2005 and 2016. They looked at factors including:
- Proximity to overhead lines
- Magnetic field exposure
- Paternal occupation
- Changes in risk over time
- Corona ion theory
- Underground cable exposures
Distance from overhead lines
This paper was published in the British Medical Journal on 3 June 2005 and gave results for distance from 275 kV and 400 kV overhead lines in England and Wales. It did not just focus on childhood leukaemia but considered all childhood cancers.
In summary, it concluded:
- Children who were born within 200 m of high-voltage power lines had a relative risk of leukaemia of 1.69, which was statistically significant.
- Those born in homes between 200 m and 600 m had a relative risk of 1.23, which was statistically significant.
- The results had a trend of decreasing risk as the birth address got further from the overhead 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.
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Magnetic field exposure
This paper, published in the British Journal of Cancer in 2010, looks at exactly the same subjects (and overhead lines) as the "distance" paper, but as well as calculating the distance from the overhead line, it also calculates the magnetic field.
For childhood leukaemia, they found a relative risk of 2 for homes with magnetic fields greater than 0.4 µT when compared to homes with magnetic fields less than 0.1 µT, which was not statistically significant because of the confidence intervals but consistent with previous studies.
Magnetic fields greater than 0.4 µT are usually only found within 50 m or so of these overhead lines. Therefore, magnetic fields seem extremely unlikely to explain the previous "distance" findings, where the elevation in risk extended to at least 600 m.
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Parental exposure
A 2012 paper looked at the father's occupation, as recorded on the birth certificate, and the subsequent risk of the child developing 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 exposure groups and you would expect some of those to be positive and some negative by chance alone.
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Changes in risk over time
This paper was a follow on to the 2005 CCRG paper and included additional data for childhood leukaemia cases between 1998 – 2008, Scottish data, and 132 kV overhead lines. They also looked at how the results changed over the decades. The summary of the results is:
- As with the original paper, there are no clear patterns of results for brain tumours or for "other cancers". All the following discussion relates to childhood leukaemia.
- 132 kV lines seemed to show similar results to the 275 kV and 400 kV lines, but there is generally a smaller effect, and it is confined to smaller distances.
- Scotland produced results consistent with England and Wales, but because the number of cases in Scotland is much smaller, the results from Scotland on their own are not statistically significant.
- The original elevated risks for childhood leukaemia extended to 600 m, the furthest distance tested, which raised the question of whether there would have been an elevation beyond that had the study looked. This follow-on study finds no elevations between 600 m and 1000 m, suggesting that the original 600 m was in fact the outer limit.
When the results are looked at by decade, the risk for childhood leukaemia seems to have diminished over time, as summarised here. The authors concluded:
“A risk declining over time is unlikely to arise from any physical effect of the powerlines and is more likely to be the result of changing population characteristics among those living near powerlines.”
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