Fields of controversy
Authors: David M Ozonoff
Journal: The Lancet (1997)

Power-frequency fields are the 50 Hz (Europe) or 60 Hz (North America) oscillating magnetic and electric fields produced when electricity is sent from the generating station via large transmission or power lines and distributed eventually to homes and businesses. Electromagnetic fields at these frequencies do not have enough energy to ionise the atoms with which they interact, and it used to be thought that biological damage was not a risk other than from very-high-power exposures that could cause thermal effects. In 1979 Nancy Wertheimer, looking at children with cancer in Denver, Colorado, noticed that the homes of these children seemed to be more “wired” than those of other children. She and Ed Leeper classified homes of cancer cases and controls by their relation to the electrical distribution system, coding the wiring in a way that they felt reflected the amount of current passing the house (and hence the degree of exposure to the magnetic component of the electromagnetic field).1Wertheimer N Leeper E Electrical wiring configurations and childhood cancer.Am J Epidemiol. 1979; 109: 273-284Crossref PubMed Scopus (1372) Google Scholar They reported a relation between the childhood leukaemia and brain cancer and their “wire codes.” The many studies of the effects of power-frequency electromagnetic fields done since then fall broadly into general population (residential) or occupational studies. Most of the residential studies have been on children, as Wertheimer and Leeper's was, but adults have been investigated too. The latest adult study is from Finland. Verkasalo et al investigated 380 000 people living within 500 m of high-voltage power lines throughout Finland. They used data from the power company to estimate exposures to annual average magnetic fields over 20 years. By linkage to the Finnish cancer registry they were able to calculate incidence rates for a variety of cancers within differing exposure levels, adjusted for age, sex, calendar year, and social class. Verkasalo and colleagues could not confirm earlier findings of increased risks of leukaemia, lymphoma, and nervous system cancers, but they did record modest excess risks from multiple myeloma in men (odds ratio 1·22) and colon cancer in women (odds ratio 1·16). Where does this leave us? A 1996 review of the epidemiological data by the US National Research Council concluded that the studies on childhood cancer done since Wertheimer and Leeper's original paper demonstrate a consistent excess of about 1·5-fold in leukaemias among children in homes with high wire code.3National Research CouncilPossible health effects of exposure to residential electric and magnetic fields. National Academy Press, Washington DC1996Google Scholar That excess is not accounted for by any known bias or confounding. The relation between a high wire code and magnetic field exposure is unclear, although, on average, high wire codes do correlate with higher exposure to magnetic fields. Moreover, analysis with the median magnetic field exposures for each wire code reveals a “dose response” for childhood leukaemias.4Poole C Ozonoff D Magnetic fields and childhood cancers: an investigation of dose response analyses.IEEE Engi Med Biol Mag. 1996; 4: 41-49Crossref Scopus (16) Google Scholar This might suggest that the adults in Verkasalo's study respond differently from children in the cancer studies. Unfortunately, the discrepancy is not so easily disposed of; other studies of adults, including a Swedish one5Feychting M Ahlbom A Magnetic fields, leukemia, and central nervous system tumors in Swedish adults residing near high-voltage power lines.Epidemiology. 1994; 5: 501-509PubMed Google Scholar done with methods similar to those of the Finnish investigation, have shown an association of some adult cancers with magnetic fields. We are here faced with a situation familar to the clinician looking at two X-ray views, one showing a suspicious lesion and another not. Is the difference due to artifact, masking of the lesion, or quality of the film ? The discrepancies in the magnetic field work are not likely to be resolved by yet more epidemiological observation in search of a biological mechanism. If we had a replicable laboratory mechanism for carcinogenesis operating at the field intensities of 50/60 Hz transmission and distribution lines—and several candidates, such as signal transduction in cells, are being investigated—many doubters might be converted.6Moulder JE Biological studies of power-frequency fields and carcinogenesis.IEEE Engi Med Biol Mag. 1996; 4: 31-40Crossref Scopus (7) Google Scholar