MAGNETIC FIELDS AND CANCER
In most countries, the electrical power systems run at a frequency of 50 Hz and at about 230 V (60 Hz and 120 V in the USA). This means that most of us, whenever we are indoors, are surrounded by a network of wires carrying alternating currents that induce corresponding alternating electric and magnetic fields. Over the last 25 years, a question that has frequently surfaced in the media is whether exposure to these electromagnetic fields (EMFs) can contribute to the development of cancers.
Concern over EMFs was aroused in 1979 by a series of epidemiological surveys that attempted to assess the strength of domestic fields and concluded that people living in houses with higher field strengths were more likely to develop cancer. The first such survey was American and the influential successors were predominantly Scandinavian. The emotional temperature of the ensuing debate was undoubtedly elevated by the fact that main cancer for which EMFs were incriminated was childhood leukaemia. Because childhood leukaemia is a very rare condition – there are about 500 new cases a year in the UK and about 2,200 in the USA – it is difficult to associate with causative factors. A second problem is that there is no known mechanism by which low-energy fields can affect biological processes. That is, unlike X-rays or even UV radiation, the energy imparted by EMFs is too low to change the structure of molecules – it cannot directly cause mutations in DNA. The most plausible mechanism advanced so far is that magnetic fields could alter the lifetime of free radicals – highly reactive species that are generated as part of the normal metabolism of living cells. Free have the potential to initiate tumour development because they can mutate DNA. However, although magnetic fields have been shown to perturb free radical formation in chemical reactions, there is no evidence that this happens in biological systems. Moreover, the field strengths required to influence chemical reactions are about 1,000 times higher than those we experience from environmental EMFs.
Public concern has led to the establishment of independent bodies both in the USA (EMF-RAPID Program) and the UK (The EMF Trust) whose remit is to support and coordinate high-quality research into EMF effects and to promote independent efforts to replicate any promising findings. Thus far there is no convincing experimental evidence that has been independently replicated showing that EMFs cause cancer.
A similar concern arising from radiation of higher frequencies has developed with the widespread use of mobile phones. These devices work in the ultra-high frequency (UHF) radio frequency (RF) range of the electromagnetic spectrum (300–3,000 MHz, wavelength 10– 100 cm). Even at these wavelengths, the energy of radiation is only about seven-millionths of an electron volt (7 μeV). Because it requires ~1 eV to break the weakest chemical bonds in DNA it seems out of the question that such radiation has direct effects on genetic material.
The major concern over mobile phones has been the suggestion that their use increases the risk of two types of a brain tumour, acoustic neuroma (Fig. 1) and glioma, and that youngsters are particularly susceptible.
1. A vestibular schwannoma visualised by magnetic resonance imaging (MRI).
As with childhood leukaemia, a major problem is that these cancers are rare in adults (one in 100,000 for acoustic neuroma and one in 30,000 for glioma) and even rarer in children. The events that cause these tumours, therefore, occur infrequently and it is difficult to show that using a mobile phone increases their probability. The ideal statistical way to tackle this sort of problem is to study a large number of people. The biggest survey so far, from Denmark, was of 420,000 people and concluded that there was no link between mobile phone use and any kind of cancer. Those who had used mobiles for over ten years showed no increased incidence of brain tumours and there was no trend of cancer development with time after first subscribing to a phone. Another Scandinavian study showed no significant increase in the incidence of brain tumours between1974 to 2003 (when there were 59,984 cases), despite the fact that from the mid-1990s on the Nordic populace took to mobile phones in a big way.
More recently still the biggest survey yet to be published came from The INTERPHONE Study Group (2010). Covering 13 countries it was set up by the International Agency for Research on Cancer (IARC) to address the question of whether mobile phones increase the risk of brain tumours within the first 10 to 15 years of use. The authors concluded that ‘Overall, no increase in the glioma or meningioma was observed with use of mobile phones’. The large cohorts in these three studies give considerable weight to their conclusions by comparison with surveys that have shown a link between mobile phones and cancer, in which the number of cases was generally very small (mostly fewer than 40).
It is appropriate to leave the last word on the risks of mobile phones to the exhaustive UK Government-commissioned Stewart report (IEGMP, 2000), an analysis by an independent group of experts of both the epidemiology and the experimental evidence relating to biological effects of mobiles. The overall conclusions were that the experimental evidence from studies on cells and animals does not suggest that mobile phone emissions, within existing International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines, have any adverse effects on health. Furthermore, the epidemiological evidence does not suggest that mobile phone emissions cause cancer nor is there any risk to people who live near base stations. Nevertheless, the period over which cancers may develop is long compared with that for which mobile phones have been in widespread use and there is evidence that mobile phone emissions may interfere with the electrical activity of the brain. For these reasons, the report recommended continued research into this question.