Results have just been published from the largest study to date of childhood leukaemia in relation to exposure to magnetic fields in the home. This important study was conducted by the US National Cancer Institute in conjunction with the Children's Cancer Group. The results of the study do not establish an association between exposure of children to magnetic fields in the home and leukaemia. The previously raised possibility of an elevated risk at higher levels of exposure to magnetic fields cannot, however, be ruled out.
The study had a number of strengths. In particular, it was based on large numbers of children: 638 diagnosed with acute lymphoblastic leukaemia (ALL) and 620 controls. Additionally, effort went into obtaining good quality exposure data and information on potential confounding factors. The exposure of the children in the study was categorised in two ways - by direct measurement of magnetic fields in and around the current and previous homes of the children and by classifying each child's home according to a "wire code". However, measurements could not be made in the homes of 22% of the eligible cases and 37% of eligible controls.
The direct measurements provided an assessment of the total time weighted average magnetic field exposure of each child. This was achieved by a combination of 24 hour measurements in each child's bedroom, spot measurements in various rooms of the home and measurements immediately outside the home, together with information about the pattern of occupancy of different rooms by the child.
"Wire codes" were assigned to homes on the basis of visual assessment from categories used in previously published studies. These categories are based on the number and type of electricity supply wires near homes and assess the potential for exposure. The researchers note the wire codes correlated with measured magnetic fields.
The study did not show a statistically significant dose-response in the risk of ALL with either measured magnetic field levels or wire codes. The odds ratio (relative risk) at fields of 0.2 microtesla or greater - as compared with less than 0.065 microtesla - was of the order of 1.2 to 1.5 depending on the method of analysis, and was 0.88 for the highest wire code category as compared with the lowest category; none of these odds ratios was statistically significant.
The Advisory Group look forward to publication of the UK Childhood Cancer Study which is examining a number of environmental factors that might be implicated in childhood cancer, including exposure to electric and magnetic fields. This is a large case-control study, involving direct measurements of exposure to magnetic fields for about 3000 cases of cancer, including leukaemia and an approximately equal numbers of controls.
First issued 15th July 1997
Last updated 13th February 1998