Approximately 80 million people in the United States alone currently use mobile telephones. Tens of thousands of new users are being added every day. This development represents an unprecedented exposure of the population to radiofrequency energy (RF). There is currently insufficient scientific evidence to assess fully whether this exposure poses any risk to human health. Should the RF exposure associated with the use of mobile telephones increase the risk of adverse health effects even slightly, the large number of users would translate into a potentially significant public health problem. In this issue, Morgan et al report the findings of a mortality study for a uniquely valuable cohort: the employees of a major manufacturer of wireless communication products. 1 They concluded that their findings do not support an association between RF exposure and brain cancer, lymphoma, or leukemia.
Currently the scientific literature relating to the health effects of low level exposure to RF does not indicate the existence of any health risk from wireless communications devices. 2 Little is known, however, about the possible health effects of repeated or long-term exposure to low level RF of the sort emitted by such devices. Some animal studies suggest the possibility for such low-level exposures to increase the risk of cancer, by mechanisms yet to be elucidated. 3 Other studies, however, while not directly contradicting these results, have not found evidence for the existence of such a risk. 4,5
Commonly available mobile telephones emit RF in either the range of 800–900 megahertz or in the range 1600–2000 megahertz. Analog telephones rely on frequency modulation (FM), while digital telephones emit pulsed RF. Many of the studies of biological effects of electromagnetic fields reported in the scientific literature were performed with other frequency ranges and modulation schemes. Because we do not know whether each frequency range has different biological effects, there is no basis for extrapolating the results found at one frequency to those of another. In particular, the comparatively large body of data pertaining to power-line frequencies cannot be used to assess the different frequencies and modulation characteristics associated with wireless communications technology. It is unlikely that it will be known whether any biological effects of analog and digital RF exposures are similar until this has been studied in long-term animal experiments. Thus far, animal experiments investigating the effects of frequencies and modulations relevant to mobile telephones are conflicting. In one particularly interesting study, however, transgenic mice exposed to a digital telephone signal developed more than twice as many nonlymphoblastic lymphomas as the unexposed control group. 6 Although the significance of these results to human health is not known, these results suggest a potential effect of the digital telephone signal on biological processes.
Studies that have assessed associations between RF exposure and human cancer were recently reviewed. 7 The review noted several reports of positive associations suggesting an increased risk of some types of cancer in those who may have had greater exposure to RF. These studies have lacked thorough exposure assessment and the results have been inconsistent. Thus, the epidemiologic evidence for a link between RF exposure and cancer remains weak.
There are almost no epidemiologic data available with which to assess whether the RF exposures characteristic of mobile telephone use may have any adverse effect on health. While one study has reported finding no evidence for an effect of hand-held mobile telephone use on all cause mortality, 8 mobile telephones have not been in widespread use long enough for long-term potential health effects to have emerged. This is especially true for hand-held telephones, which generally give a higher RF exposure than do other types of mobile telephones.
Recent recommendations for epidemiologic research to address these issues have emphasized studies of highly exposed populations, such as occupationally exposed groups or cohorts of mobile telephone users. 9,10 Such an approach, which increases the sensitivity to adverse health effects, has been taken by Morgan and co-workers. Their study cohort comprised employees at a company involved in the design, manufacture, testing, and use of a variety of wireless communications devices under the reasonable assumption that this group has a higher likelihood of RF exposure than the general population. They found no elevation in mortality for brain cancers or all lymphatic/hematopoietic cancers combined. The size of the cohort, the rarity of these diseases, and other factors made it impossible for the authors to rule out potential relative risks as low as 1.5 to 2.0, but the study does provide useful evidence regarding large health effects.
Morgan and co-workers also provide in their report a concise, informed introduction to the technology and issues that provide context for research on RF safety. To characterize the RF exposure of cohort members, they used classifications based on semi-quantitative expert opinions of exposure levels that might generally apply to job type. They described exposure to RF in terms of all RF exposure without distinguishing different frequency or modulation characteristics. While this grouping limits the ability to demonstrate whether particular RF sources might be associated with disease outcomes, the situation is not unique. Epidemiology studies of RF exposure have relied on qualitative classifications of RF exposure, with only a few including even limited RF measurements. Given the novelty and increasing proliferation of RF exposures from mobile telephone use, a more notable limitation of the present study is the absence of information on mobile telephone use or RF exposures arising from such use. As noted above, the cohort studied by Morgan et al could be expected to have had higher RF exposures than the general public. This pattern would also be expected to apply to RF exposures from mobile telephone technology in part due to early (and perhaps less expensive) access to new technologies. Thus, it stands to reason that the cohort might be exceptionally informative for assessments of the possible health risks associated with mobile telephones.
Exposure assessment appears to be the most troublesome aspect of RF studies. A recent workshop on the topic highlighted the many difficulties in this area that impede attempts to study whether any health risk is related to mobile telephone use. 11
There is currently insufficient scientific basis for concluding whether wireless communication technologies pose any health risk. A significant research effort, involving both large, well-planned animal experiments and epidemiologic studies of exposed populations, is needed to support risk assessment of these devices. The study of Morgan and co-workers is a useful beginning.
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