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Safety in electric, magnetic and electromagnetic fields (relating to environmental electromagnetic compatibility) 

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Systematic review on the health effects of exposure to radiofrequency electromagnetic fields from mobile phone base stations

Martin Röösli a, Patrizia Frei a, Evelyn Mohler a & Kerstin Hug a

a. Swiss Tropical and Public Health Institute and University of Basel, Socinstrasse 59, Basel, CH-4002, Switzerland.

Correspondence to Martin Röösli (e-mail: [email protected]).

(Submitted: 10 September 2009 – Revised version received: 06 May 2010 – Accepted: 07 May 2010 – Published online: 05 October 2010.)


Bulletin of the World Health Organization 2010;88:887-896F. doi: 10.2471/BLT.09.071852

Introductions

The introduction in the 1990s of mobile phones using the digital Global System for Mobile Communications (GSM) with bandwidths of 900 and 1800 megahertz and the subsequent introduction of the Universal Mobile Telecommunications System (UMTS) have led to widespread use of this technology and to a substantial increase in the number of mobile phone base stations (MPBS) all over the world. This development has raised public concerns and substantial controversy about the potential health effects of the radiofrequency electromagnetic field emissions of this technology.13 A small proportion of the population attributes non-specific symptoms of ill-health, such as sleep disturbances or headache,2,4 to exposure to electromagnetic fields. This phenomenon is described as electromagnetic hypersensitivity or “idiopathic environmental intolerance with attribution to electromagnetic fields.”58 Additionally, individuals who are hypersensitive to electromagnetic fields often claim to be able to perceive radiofrequency electromagnetic fields in their daily life.6


People are generally exposed to MPBS radiation under far-field conditions, i.e. radiation from a source located at a distance of more than one wavelength. This results in relatively homogenous whole-body exposure. MPBS exposure can occur continuously but the levels are considerably lower than the local maximum levels that occur when someone uses a mobile phone handset.9 A recent study that measured personal exposure to radiofrequency electromagnetic fields in a Swiss population sample demonstrated that the average exposure contribution from MPBSs is relevant for cumulative long-term whole-body exposure to radiofrequency electromagnetic fields. However, as expected, it is of minor importance for cumulative exposure to the head of regular mobile phone users.10(Personal exposure measurements assess the total radiation absorbed by the whole body, whereas spot measurements quantify short-term exposure in a single place, usually the bedroom.)


In 2005, the World Health Organization (WHO) organized a workshop on exposure to radiation from MPBSs and its health consequences and subsequently published a paper summarizing the state of knowledge on the matter.11 At that time, studies about the health impact of MPBS emissions were scarce and of low quality because most of the previous research on the health effects of radiofrequency electromagnetic fields had focused on exposure to mobile phone handsets and on effects related to head exposure, such as brain tumours or changes in brain physiology. In the last four years, research efforts have increased in response to public complaints and to a Dutch study describing decreased well-being associated with UMTS base station exposure.12 Acute effects have been investigated in healthy volunteers and in individuals with hypersensitivity to electromagnetic fields using randomized, blinded laboratory trials and field intervention studies. Further epidemiological research has been stimulated by the recent availability of personal exposure metres. The aim of this paper is to present a systematic review of the scientific literature concerning all the health effects of MPBS radiation that have been investigated to date.

Methods

Literature search

We conducted a systematic search of Medline, EMBASE, ISI Web of Knowledge and the Cochrane Library in March 2009 to identify all relevant peer-reviewed papers published before that date. Key and free-text words included “cellular phone,” “cellular,” “phone,” “mobile” and “mobile phone” in combination with “base station(s).” In addition, we examined references from the specialist databases ELMAR (http://www.elmar.unibas.ch) and EMF-Portal (http://www.emf-portal.de), reference lists in relevant publications and published reports from national electromagnetic field and mobile phone research programmes.

Inclusion and exclusion criteria

We included human laboratory trials and epidemiological studies, and we considered all the health effects that have been addressed so far. These include self-reported non-specific symptoms (e.g. headache, sleep disturbances, concentration difficulties), physiological measures (e.g. hormone levels, brain activity), cognitive functions, genotoxicity, cancer and various chronic diseases. In addition, we included randomized double-blind trials evaluating whether study participants were able to perceive radiofrequency electromagnetic fields. For a study to be eligible, far-field exposure from MPBSs had to be investigated – i.e. a relatively homogenous whole-body field in the GSM 900, GSM 1800 or UMTS frequency range – and the relationship between exposure and outcome had to be statistically quantified. In addition, basic quality criteria had to be fulfilled. Trials had to apply at least two different exposure conditions in a randomized and blinded manner. Epidemiological studies had to quantify exposure using objective measures (such as distance to the nearest MPBS, spot or personal exposure measurements, or modelling), possible confounders had to be considered and the selection of the study population had to be clearly free of bias in terms of exposure and outcomes

Data extraction

The data from each study were extracted independently by two researchers and recorded on one of two standardized forms. These forms, one for randomized trials and one for epidemiological studies, were developed using the CONSORT statement13 for trials and the STROBE statement14 for epidemiological studies. Extracted data included information about study participants, selection procedure, study design, exposure, analytic methods, results and quality aspects. Differences concerning data extraction were resolved by consensus.

Meta-analysis

All reported outcomes were checked for meta-analysis suitability. The only outcome with a sufficient number of comparable studies was the ability to perceive radiofrequency electromagnetic field exposure. To combine these study outcomes, for each study we calculated the difference between the number of observed correct answers (O) and the number of correct answers expected by chance (E), normalized by the number of correct answers expected by chance ([O-E]/E). Exact 95% confidence intervals (CIs) were calculated on the basis of binomial or Poisson data distribution, depending on the experimental design. In the absence of heterogeneity between studies (I2 = 0.0%; P = 0.99), we used fixed-effect models for pooling the study estimates. The detailed method is described in Röösli, 2008.6


Evidence rating

To rate the evidence for detrimental health effects from MPBSs, we assessed the risks of various types of bias for all included studies as proposed by the Cochrane handbook.15 The final evidence rating was obtained according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.16


Results

Selection of studies

In total, 134 potentially relevant publications were identified; 117 articles were excluded as they did not meet our inclusion criteria (Fig. 1). Of the 17 articles included in the analyses, 5 were randomized trials and 12 were epidemiological or field intervention studies. The majority of the studies examined non-specific symptoms.


Fig. 1. Flowchart showing the identification and selection of studies on the health effects of exposure to radiofrequency electromagnetic fields from mobile phone base stations

Non-specific symptoms of ill-health

Acute effects of MPBS exposure on self-reported non-specific symptoms were investigated in four randomized double-blind human laboratory trials. The details of these studies are summarized in Table 1 (available at: http://www.who.int/bulletin/volumes/88/12/09-071852). Three trials used a UMTS antenna to create controlled exposure circumstances17,19,20 and one study evaluated all three mobile phone frequency bands.18 In total, 282 healthy adults, 40 healthy adolescents and 88 individuals with hypersensitivity to electromagnetic fields were included in these four studies. Exposure levels varied between 0.9 and 10 volts per metre (V/m).



We identified 10 epidemiological studies that investigated the effect of MPBS exposure in terms of self-reported non-specific symptoms (Table 2, available at: http://www.who.int/bulletin/volumes/88/12/09-071852). Most of these studies were cross-sectional, and the magnitude of the exposure was based on the distance between place of residence and the nearest MPBS,1,27 or on spot measurements of MPBS radiation in the bedroom,24,35 or on personal measurements of exposure to radiofrequency electromagnetic fields over a 24-hour period.31,39 Four epidemiological studies applied an experimental approach (field intervention) in which exposure was modified either by turning on and off an MPBS28,29 or by using shielding curtains.30,33 Sample size ranged from 43 to 26 039 participants. The cut-off values differentiating exposed from unexposed persons varied between 0.1 and 0.43 V/m.



Of all non-specific symptoms, headache was most often investigated (Table 3). Two epidemiological studies24,27 reported a statistically significant positive correlation between exposure level and headache score. In a Danish laboratory trial, when the data from 40 adults and 40 adolescents were pooled, a larger change in headache score was found under UMTS exposure than under sham exposure.19 However, further analysis indicated that this change was due to a lower baseline score before UMTS exposure rather than to a higher score after exposure. The remaining four epidemiological studies28,31,35,39 and one laboratory trial17 did not indicate any association between MPBS exposure and headache.



With respect to self-reported sleep measures, only an Egyptian study27 reported greater daytime fatigue in exposed individuals. None of the other studies found any association between MPBS exposure and fatigue or self-reported sleep disturbances (Table 4).20,24,2931,35,39


Many other non-specific symptoms have been evaluated, such as concentration difficulties or dizziness. Generally, no association with exposure was observed (Table 1 and Table 2). One of the few exceptions was a laboratory trial that showed an increased arousal score among individuals with hypersensitivity to electromagnetic fields during UMTS exposure, which might be explained in part by the effect of order of exposure rather than by exposure itself.18 One field intervention study observed a small increase in calmness under unshielded conditions compared with shielded conditions, but no effect on mood or alertness.33 In an observational study from Egypt, several symptoms were more prevalent in 85 inhabitants or employees of a house near an MPBS compared with 80 employees considered unexposed.27 In an Austrian study with 365 participants, a statistically significant association was found between 3 out of 14 symptoms (headache, cold hands and feet, concentration difficulties) and MPBS exposure.24


Some studies evaluated overall symptom scores obtained from standardized questionnaires such as the SF-36 Health Survey,37 the Von Zerssen list25 and the Frick symptom score38 (Table 5). In a survey of 26 039 German residents, the Frick symptom score was significantly elevated for people living less than 500 m from an MPBS compared with those living further away.1 However, subsequent improved dosimetric evaluations in 1326 randomly selected volunteers from this survey did not confirm a relationship between symptoms and measured MPBS radiation.35 Three additional studies also failed to find any association between exposure and symptom scores.17,18,28


In summary, when data from all the randomized trials and epidemiological studies were considered together, no single symptom or symptom pattern was found to be consistently related to exposure. The cross-sectional epidemiological studies, however, showed a noteworthy pattern: studies with crude exposure assessments based on distance showed health effects, whereas studies based on more sophisticated exposure measurements rarely indicated any association.