Methodological limitations in experimental studies on symptom development in individuals with idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF) – a systematic review

Abstract

BackgroundHypersensitivity to electromagnetic fields (EMF) is a controversial condition. While individuals with idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF) claim to experience health complaints upon EMF exposure, many experimental studies have found no convincing evidence for a physical relation. The aim of this systematic review was to evaluate methodological limitations in experimental studies on symptom development in IEI-EMF individuals that might have fostered false positive or false negative results. Furthermore, we compared the profiles of these limitations between studies with positive and negative results.MethodsThe Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guided the methodological conduct and reporting. Eligible were blinded experimental studies that exposed individuals with IEI-EMF to different EMF exposure levels and queried the development of symptoms during or after each exposure trial. Strengths and limitations in design, conduct and analysis of individual studies were assessed using a customized rating tool.ResultsTwenty-eight studies met the eligibility criteria and were included in this review. In many studies, both with positive and negative results, we identified methodological limitations that might have either fostered false or masked real effects of exposure. The most common limitations were related to the selection of study participants, the counterbalancing of the exposure sequence and the effectiveness of blinding. Many studies further lacked statistical power estimates. Methodically sound studies indicated that an effect of exposure is unlikely.ConclusionOverall, the evidence points towards no effect of exposure. If physical effects exist, previous findings suggest that they must be very weak or affect only few individuals with IEI-EMF. Given the evidence that the nocebo effect or medical/mental disorders may explain the symptoms in many individuals with IEI-EMF, additional research is required to identify the various factors that may be important for developing IEI-EMF and for provoking the symptoms. We recommend the identification of subgroups and exploring IEI-EMF in the context of other idiopathic environmental intolerances. If further experimental studies are conducted, they should preferably be performed at the individual level. In particular, to increase the likelihood of detecting hypersensitive individuals, if they exist, we encourage researchers to achieve a high credibility of the results by minimizing sources of risk of bias and imprecision.Electronic supplementary materialThe online version of this article (10.1186/s12940-019-0519-x) contains supplementary material, which is available to authorized users.

Co‐Designed Exposure Protocol in the Study of Idiopathic Environmental Intolerance Attributed to Electromagnetic Fields

“…Conducting tests on an individual level is recommended [Schmiedchen et al, 2019] but requires a higher number of repetitions of real or sham exposure sessions and a higher time investment from the participants. Most participants expressed their willingness to take part in a sufficient number of tests to obtain a sufficiently high statistical power at the individual level provided that they were able to perceive the EMF exposure.…”

“…The hypothesis of an electromagnetic origin of such symptoms has been widely investigated by provocation studies, which consist of deliberately exposing people with IEI‐EMF to particular EMF sources in laboratory settings to observe the volunteers’ reactions. In the majority of studies, these reactions have been found to be independent of exposure: people with IEI‐EMF did not perceive EMF beyond chance, did not get more symptoms during real rather than sham exposures [Rubin et al, 2010; Schmiedchen et al, 2019], and did not react physiologically (heart rate variability, skin conductivity, cognitive functioning, etc.) differently to real and sham exposure [Rubin et al, 2011; Andrianome et al, 2017].…”

“…On the basis of a critical review of provocation studies, Schmiedchen et al [2019] found that there are just a few high‐quality studies and that most studies suffer from design and methodological limitations that might bias their findings or reduce their accuracy. The most common issues relate to the selection of study volunteers in relation to the symptoms being observed and exposure parameters, e.g.…”

“…Similarly, McCarty et al [2011] suggested that individuals with IEI‐EMF respond more to changes in state, i.e., transitions between real and simulated exposure, than to the exposure itself. The few provocation studies that reported a statistically significant finding often indicate a protective effect of exposure as a detrimental effect on symptoms, which might be due to chance or methodological issues [Schmiedchen et al, 2019]. Therefore, to this end, the studies that potentially reflect a true connection between EMF exposure and symptoms are insufficient as evidence that EMF hypersensitivity may occur as an environmentally inducible syndrome.…”

“…However, provocation studies should be pursued with more appropriate methodologies, as several authors have attempted in recent years using innovative methods, such as by considering the comments and suggestions of people with IEI‐EMF [Huss et al, 2016; Andrianome et al, 2017; van Moorselaar et al, 2017] and by adapting the exposure system and the test environment to their conditions [van Moorselaar et al, 2017; Verrender et al, 2018]. Schmiedchen et al [2019] emphasized that such studies should only be conducted if their methodology is carefully considered.…”