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Electromagnetic fields and cancer<P>Can the electromagnetic fields in a Volvo car cause cancer? Are electromagnetic fields at all capable of inducing cancer? <P>In a widely publicised Swedish survey conducted some 10 years ago, the association between living in the proximity of power lines and cancer in children was studied. There was no relation between electromagnetic fields with respect to the overall cancer incidence, nor for lymphomas, or for tumours of the central nervous system. For leukaemia in children living in one family homes – but not for those living in apartment houses – the number of observed cases was higher than expected for a very small subset of 39 leukaemia cases. However, the calculated risk depended on how these cases were grouped with respect to the distance from the power lines, and the authors themselves pointed out that their estimates were “unstable”. However, the results of the epidemiological surveys that so far have been conducted have been highly contradictory. Thus, in a more extensive study encompassing 399 cases of leukaemia in children with exposure assessment including personal field monitoring, and that was conducted recently by the British Columbia Cancer Agency in Vancouver, Canada, no significant risk could be shown at all. <P>It should be born in mind, that it is very difficult to eliminate all potential sources of error that stem from bias and confounding by using conventional methods in this type of epidemiological studies. This was illustrated in a striking way by a California investigation on the cause of leukaemia in 232 children from 1994, and which was conducted by epidemiologists from the National Institutes of Occupational Safety and Health, Cincinnati, and the University of Southern California. After adjustment of confounders, only one statistically highly significant and persistent association was found: children who consumed 12 hot dogs or more per month had a 9.5-fold (!) higher risk of leukemia, and when referring to the father’s intake of hot dogs, the risk for the child to develop leukaemia was increased 11 (!) times. Common sense dictates that the eating of hot dogs could hardly have been the cause of leukemia, but that excessive eating of sausages was an indicator of other factors that lie closer to the true cause, e.g. an unhealthy lifestyle characterizing these childrens´ homes with inferior diet, infections during the mother’s pregnancy, etc. <P>The WHO International Agency for Research on Cancer (IARC) in Lyon has taken up low frequency electromagnetic fields for evaluation, and although the report has not yet been published its conclusions have already been distorted by the media. It is not clear to which extent well-known experts in the field of radiation biology participated, but in view of the fact that IARC undoubtedly has considerable experience in epidemiology, it is worthwhile to relate the Agency’s main judgements. IARC said that “There is inadequate evidence that electric fields are associated with childhood leukaemia, and there is no consistent relationship between childhood brain tumours or other childhood solid tumours.” However, the Agency judged that there was limited epidemiological evidence for an association between high residential magnetic field strenghts and childhood leukaemia, but points out that the results “may be affected by selection bias.” The IARC official statement goes on to say “There is no consistent evidence that residential or occupational exposures of adults are related to excess of cancer at any site. Evidence for excess cancer risks of all other kinds, in children and in adults, as a result of exposure to extremely low frequency electric and magnetic fields was considered inadequate.“ <P>Exemplified by the very strong association between the possession of ashtrays and risk for lung cancer, a statistical link does not necessarily mean that there is a causal link. In this case, available epidemiological data are far from sufficient, and there are also other important reasons to reject the existence of a real cause-and-effect relationship. All elementary textbooks in epidemiology emphasise, that to be able to establish a causal relationship there must some kind of plausible mechanism that explains how the effect can come about. In other words, the link must be biologically credible. This is something that some epidemiologists tend to forget. Even if there is no shortage of speculations on the subject, nobody has yet succeeded in establishing a single probable mechanism that explains how electromagnetic radiations can induce cancer. The laws of physics tell us that the energy is simply too low to cause any kind of chemical reaction necessary for this to occur, e.g. provoking mutations. IARC states: “.. no scientific explanation for carcinogenicity of these fields has been established.”<BR> <BR>Testing in animals constitutes another important way to support a cause and effect relationship. All high-energy radiations, as well as all chemical substances that so far have been shown to be carcinogenic in humans, will also induce tumours in laboratory animals. Arsenic is possibly one exception, but this enigmatic carcinogen instead functions as a tumour promoter. It has not been possible, despite considerable efforts, to credibly establish that electromagnetic fields cause cancer, or promote the growth of tumours in animals. Also, there are no adequate evidence that these fields induce mutations under controlled conditions. According to IARC “Overall, evidence for carcinogenicity of electromagnetic fields in experimental animals was judged inadequate.” In all, IARC finds very little support for a causal relationship, and as was recently the case for the pesticide amitrol, the classification “limited evidence” can later be revoked based on mechanistic considerations in favour of “insufficient evidence”. <P>Finally, it must be emphasised that even if a small risk associated with electromagnetic fields existed – which I myself and most of my colleagues strongly doubt – then this risk would in any case be virtually negligible. The 39 cases of children’s leukaemia identified in the Swedish study cited above, occurred over a period of 25 years among the 100,000 or so Swedish children who lived in the vicinity of power lines. The excess risk attributed to electromagnetic fields corresponds approximately to 3-5 additional cases over a quarter of a century. The probability of a child being killed by lightning is probably considerably greater. This same period saw about 750,000 cases of cancer among the general Swedish population caused by other reasons. Of this figure, about 250,000 can be traced to diet, probably as many stem from hereditary causes in combination with other factors, and about 110,000 can be traced directly to smoking. <P>The electromagnetic field measured in a Volvo does not exceed 18 micro Tesla. This is less than the Earth’s own magnetic field to which everybody is exposed from cradle to grave, and which varies from 25 micro Tesla at the equator to 65 micro Tesla at the poles. Considering all kinds of real risks associated with driving a car, insignificant and hypothetical risks from the electromagnetic field in a Volvo would seem to be the least of all concerns. <P>Stockholm, February 23<P>Robert Nilsson<P>Adjunct Professor in Molecular Toxicology and Risk Assessment and Assistant Professor in Radiation Biology, Department of Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University , Stockholm, Sweden<BR>Professor of Toxicology, Nofer Institute of Occupational Medicine and WHO Collaborating Centre, Lodz, Poland<BR>
 
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