Background Hypersensitivity 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. Methods The 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. Results
Twenty-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. Conclusion Overall, 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.