Bunch et al (2014) studied the incidence of childhood leukaemia in relation to distance at birth from high-voltage powerlines over the period 1962–2008 and found that, for children born within 200 m, the relative risk fell from 4.5 (0.97–20.83) in the 1960s to 0.71 (0.49–1.03) in the 2000s.

The opening year of the study was the last in which there was insufficient capacity to meet the maximum demand for electricity (Department of Energy and Climate Change (DECC), 2013). The next decade saw a near doubling of demand which drove a frenzied programme of power station and power line construction, (National Grid Company, 2010) and, by the time that the 1973 oil crisis forced a slow down, a 50% margin of generating capacity over the peak demand had been established (Department of Energy and Climate Change (DECC), 2013).

Construction of the 400 kV supergrid did not begin until 1965 and it is noteworthy that Bunch et al’s maximum relative risk of 4.5 (0.97–20.83) relates to the period 1962–1999 when construction activity would have been intense. This activity was reliant on an influx (which included this author) of itinerant workers to the communities hosting the construction sites and the population mixing associated with this influx has been associated with the incidence of childhood leukaemia (Kinlen et al, 1995; Kinlen and Doll, 2004).

Kinlen et al studied the incidence of childhood leukaemia within 10 km of large, rural, construction sites and five of their chosen locations (Drax, West Burton, Longannet, Pembroke and Fawley) housed power stations and supported an on site construction work force of more than 2000 during the first decade of Bunch’s study.

To quote from Kinlen’s abstract:

A 37% excess of leukaemia and non-Hodgkin’s lymphoma at 0–14 years of age was recorded during construction and the following calendar year. The excesses were greater at times when construction workers and operating staff overlapped (72%), particularly in areas of relatively high social class. For several sites the excesses were similar or greater than those near the nuclear site of Sellafield (67%), which is distinctive in its large workforce with many construction workers.

The reader may object that Bunch et al were considering the impact of power lines, not power stations but all of the power stations under consideration were connected to the National Grid and powerlines would, necessarily, have run through the areas which Kinlen et al identified as having an elevated relative risk of childhood leukaemia.

He concluded that:

Overall these findings provide further support for the hypothesis that rural population mixing is conducive to the transmission of the underlying infective agent(s) among susceptible people so as to increase the incidence of childhood leukaemia and non-Hodgkin’s lymphoma.

The consumption of electricity in the UK grew by a factor of nearly three between 1962 and 2008 (Department of Energy and Climate Change (DECC), 2013), whilst Bunch et al show that the relative risk of leukaemia declined, from 4.5 to 0.71, over the same period. There can be little debate over their observation that magnetic fields cannot provide an explanation for their findings.

Bunch et al did not consider the relatively short term impact of the influx of powerline and power station construction workers but rather suggest that the result may be due to the ‘changing population characteristics of people living near powerlines.’ Power stations are nodes on the powerline network and, of course, the lines are remote from them for much of their length. The authors mention ‘changes to the types of houses built near powerlines or the characteristics of people living in them’ as possible causes of their findings. These changes would have taken time but the maximum relative risk of leukaemia was found in the early years of the study when the influx of contractors would have been at its height.

Kinlen’s data show that mixing can enhance the risk of leukaemia in the relatively short term (1970–75 at Drax Phase 1, 1968–73 at Longannet, 1966–68 at West Burton). His cases were drawn from the same registry as Bunch’s and it would be of great interest to locate the totality of Bunch et al’s exposed cases with respect to the power stations as well as the powerlines.