1. Claudio Gómez-Perretta1,

Abstract

Strengths and limitations of this study

• We used a robust statistical analysis with a highly homogeneous sample in a homogeneous environment.

• A participation bias cannot be ruled out. The late query about concerns (as a possible confounder) may render the results less valid.

• We observed that the incidence of most of the symptoms was related to exposure levels.

The health risk due to exposure to radiofrequency electromagnetic fields (RF EMFs) continues to be discussed today. The study that led to this debate was initiated after verification that the US embassy in Moscow was being subjected to such radiation from 1953 to May 1975.1 Recently, a review of that episode2 reopened the debate about the potential harmfulness of RF EMFs. The increasing number of base stations (BSs) on masts and buildings has increased public awareness. This issue has prompted scientific research to establish to what extent low-intensity EMFs may affect the health of humans and other organisms.3 ,4 Furthermore, the term electromagnetic hypersensitivity has been recently introduced in discussions attributing symptoms to exposure to EMFs.5-8 A review of this topic9 in 2010 found that 8 of the 10 studies evaluated through PubMed had reported increased prevalence of adverse neurobehavioral symptoms or cancer in populations living at distances <500”…m from BSs.

None of the studies reported exposure above accepted international guidelines, suggesting that current guidelines may be inadequate in protecting health. Thus, the need emerges to revaluate our pioneering work in this field in order to add new procedures and data. Few articles have addressed the possible association between microwave sickness and microwave exposure from Global System for Mobile Communications (GSM) BSs since the publication of our first study.10 Chronologically, Santini et al11 and Gadzicka et al12 reported differences in the distance-dependent prevalence of symptoms such as headache, impaired concentration and irritability. A later Austrian study13 showed a positive association between the measured electrical field (GSM 900/1800) in bedrooms and headaches, cold hands and feet and difficulties in concentration. An Egyptian study14 showed a prevalence of neurological symptoms, such as headache, memory changes, dizziness, tremors, depressive symptoms and sleep disturbances among participants directly exposed to GSM signals from BSs.

The symptoms reported by all the above cited authors belong to those attributed to the microwave syndrome.15 However, one article16 using personal monitored data from GSM-UMTS frequency bands found no statistical association in adults. More recently, the same authors observed no association in children,17 contradictory results in children and adolescents,18 and concluded that the few observed significant associations were not causal but rather occurred by chance. Blettner et al19 reported in phase 1 of their study more health problems closer to BSs, but in phase 220 they concluded that measured EMF emissions were not related to adverse health effects.

Other researchers focused their work on the possible existence of participants with sensitivity to GSM or UMTS signals according to psychological, cognitive or autonomic assessment. These researchers used short-term exposure (only 30-50”…min) under laboratory conditions21-23 and revealed a large disparity between participants. Recently, a study measuring several biological stress markers24 found that RF EMF emitted by mobile phone BSs from 5.2 to 2126.8”…μW/m²increased cortisol and salivary α-amylase, while IgA concentration was not significantly modified.

The Selbitz study25 in 2010 described a significant dose-response relationship in symptoms related with sleep, mood, joints, infections, skin condition, as well as neurological, cardiovascular, visual and auditory systems and the gastrointestinal tract.

The existence of short-term physiological effects of EMF on sleep quality was not evident in the work of Danker-Hopfe et al26; however, it was stated that the presence of BSs per se (not the EMF) may have a negative impact on sleep quality.

A Polish study in 2012 did not show a correlation between electrical field strength and frequency of subjective symptoms; however, it showed a correlation between subjective symptoms and the distance to BSs.27 A study carried out in Egypt28 revealed that exposure to EMF emitted either from mobile phones or BSs had significant effects on the pituitary-adrenal axis. More recently, work developed in Iran29 indicated that symptoms such as nausea, headache, dizziness, irritability, discomfort, nervousness, depression, sleep disturbance, memory loss and lowering of libido were statistically significant in people living near BSs (<300”…m distances) compared with those living far from the BSs (>300”…m).

In our cross-sectional analysis,10 11 of 16 symptoms showed statistically significant higher scores in the group with the maximum exposure level. The symptoms are included in the microwave syndrome. We also reported statistically significant correlation coefficients between the measured electrical field and 14 of 16 symptoms.

A review30 recently established several conditions for epidemiological studies to be eligible for introduction in general analysis: eligible studies must quantify exposure using objective measures (such as distance to the nearest BS, spot or personal exposure measurements in a specific frequency range); possible confounders must be considered and the selection of the study population must be clearly free of bias in terms of exposure and outcomes.

Accordingly, in this reanalysis of our previous study,10 possible confounders were included in addition to the specific RF EMF measurements made in 2001 (covering the specific range between 900 and 1800”…MHz). Therefore, we coanalysed the effects of other variables such as sociodemographic data and the use of electronic devices. Concern about being damaged by radiation from antennas was also analysed.

The new statistical approach tested the possible influences of other variables, such as demographic data and the use of electronic devices. Moreover, since some concerns have been raised about possible health consequences caused by the emitted microwaves, we analysed whether these symptoms might be related to fear of exposure. As some participants refused to allow measurements in their homes, we analysed whether symptom status or subjective distance to the BS could be a bias of participation in the study. Interestingly, this period was free of other sources of RF such as WIFI or UMTS or the massive use of mobile phones, enabling a specific study of GSM technology. Finally, the suitability of the size of the sample was analysed.

Methods

Results

Demographic data and the percentage of users of personal computers and mobile phones were analysed. The mean age was 42 and 17”…years (SD±17. 61, interval 15-81). Women totalled 51.1% (mean age=45.08”…years, SD=17.98; interval=15-81) and 48.9% were men (mean age”‰=”‰39.12”…years, SD=16.88; interval=15-75). A total of 13.6% participants regularly used computers and 23.9% used mobile phones.

No differences related with age and use of mobile phones or computers were found between the sexes.

The univariate logistic regression indicated that age was inversely associated with irritability (OR=0.97, 95% CI 0.95 to 0.99) and that the oldest had the greatest difficulties hearing (OR=1.03, 95% CI 1.01 to 1.06) and walking (OR=1.04, 95% CI 1.01 to 1.07). However, gender clearly did not influence the outcome of any dependent variable. Use of mobile phones was linked with lack of appetite and vertigo, while worry about the radiation from BSs was associated with trouble sleeping (table 1). However, concern about radiation from BSs was unrelated to age (ANOVA test), sex (λ statistic) or subjective distance to BS (Somers’ D statistic).

Most of the symptoms were related with GSM exposure, especially fatigue, irritability, lack of appetite, trouble sleeping, depression and lack of concentration. Change in -2 log likelihood showed similar results (table 2). Figure 1 shows the distribution of EMF measurements throughout the sample.

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Figure 1

Distribution of electromagnetic field (EMF) measurement throughout the sample.

ROC curves for each of the logistic regression models (GSM exposure vs each symptom) oscillated between 0.65 and 0.87 (table 3). Headaches (0.84), nausea (0.86), appetite (0.87) and vascular problems (0.85) showed the highest values, while memory (0.67), skin (0.67) and visual disturbances (0.65) showed the lowest values. The Hosmer and Lemeshow test indicated that most analyses showed no significant p values. The exceptions were fatigue (0.003), depression (0.003) and vertigo (0.03). In the majority of the cases, the models predicted better specificity than sensitivity. Only in the case of headaches and sleep disorder, did sensitivity prevail over specificity (table 3””classification table). In the extreme case, skin and vascular problems showed null or minimum sensitivity and 100% specificity. Nagelkerke pseudo R²showed acceptable coefficients with the exception of the symptoms related with vertigo and skin problems (table 3).

Threshold cut-off values of GSM for sleep, attention, irritability and memory are also shown (table 3). The remaining cut-off values were not considered since sensitivity or specificity was reported at below 0.50%.

The influence of other covariates on the GSM ORs coefficients, such as age, cellular use and concern about the BS, was always less than 10% (table 2).

There was no observed multicollinearity among variables. The κ values according to factor analysis were always lower than 2 and well below the critical value of 30.

Finally, no interactions between covariates were observed.

SEs and CIs obtained by resampling were similar to those calculated from the asymptotic approximation (table 4). There was a small bias or difference between the average bootstrap coefficients (not shown) and the respective estimates obtained from the original sample.

There were no global health differences between those who permitted a bedroom exposure measurement (88 in our previous model) and those who refused RF measurements (26), and these results were unaltered when using age as a covariate. Square partial eta measured a 0% contribution of the willing participation variable to symptoms, such as irritability, headaches, walking difficulties and hearing loss that correlated with age. There was no relationship between subjective distance to the BS and willingness to participate (Pearson χ²=2.80, df=1; p=0.094).

However, ANOVA showed that the group with recorded RF EMF levels was more prone to symptoms of memory loss (F=5.07; p=0.027), while participants without EMF measures showed more skin problems (F=10.66; p=0.001).

Discussion

In the present reanalysis, a more robust statistical method was employed that was indifferent to the assumption of normality. To reduce the limitation of the sample size effect and extrapolate our results to the entire population from which the sample was obtained, a resample method or bootstrapping was used.

This new study partially confirms our preliminary results””namely, that most of the symptoms are related to GSM levels independent of the demographical variables and some possible risk factors. Related to microwave radiation, the spectral power density analysis maintained that the most important contribution to broadband measurements was from GSM 900/1800, and the main variability of the measurements between different places was due to a different coverage of the GSM 900/1800 signals, that is, spatial variability. This was further supported by the fact that the antenna used was fairly insensitive to frequencies below 400”…MHz. Therefore, the radio channels 80-110”…MHz were not a significant part of the broadband measurements. Moreover, the narrow band measurements showed TV channels with substantially lower intensities than the GSM 900/1800 signals. The effects from these exposures will therefore not confound the effects of BSs. Moreover, some authors13 found that the only relevant contribution to the variance of the high microwave exposure was from BSs””up to 93% of variance. Moreover, at the time of our study, the GSM signal was almost invariable in time because there were very few calls. The main contribution was made from the broadcast channels working almost constantly throughout the day. Short-range evaluations of exposure could be acceptable for describing a 24”…h period and the measurements were made in bedrooms””a location where the participants were assumed to spend significant periods of time.

However, some participants were mobile phone users at the time of this study and exposure to a mobile phone during a phone call is much higher than that received from BSs. Nevertheless, some authors13 stated about that there is no a priori argument why these lower levels should have no effect on the presence of a widespread use of mobile telephones. Exposure to a BS will be at a low but almost constant level for many hours of the day and especially at night.

While GSM exposure was associated with most of the symptoms, walking difficulties and hearing loss were correlated only with age. Age also remained slightly inversely associated with irritability. Users of cellular phones were more prone to symptoms of loss of appetite and vertigo, while those who expressed worry about the BSs were associated with sleep problems. This later finding was in concordance with two other articles.13 ,20 ,26 However, worry about the BSs was unrelated with age, gender or subjective distance to BSs. This agrees with an article36 claiming that there was no statistically significant association between symptom occurrence associated with perceived proximity to BSs, psychological components, sociodemographic characteristics and distance to BSs or power lines.

Some authors indicated that opponents of mobile phone towers generally do not express anxieties about EMF exposure, indicating that the risk rating is comparable with other commonly perceived hazards in the modern world.37

None of the analysed covariates behaved as confounders. The relationship of GSM exposure with irritability, sleep troubles, lack of appetite and vertigo remained statistically significant despite the introduction of the above covariates.

When the conventional multivariate analysis was tested using bootstrapping it was observed that the SE and CIs obtained by resampling were similar to those calculated from asymptotic approximation and this supports the adequacy of our conventional analysis. Our sample, chosen at random, represents the population from which it came.

The model appeared generally well adjusted while the cut-off values could constitute good guidance for predicting the threshold of symptom appearance.

We cannot truly state that residents were more worried, equally worried or less worried than elsewhere in this region, since we cannot provide the percentage of those worried about the BS masts in La Ñora compared with other nearby places. However, information about this issue was widespread in this region at the time, and the circumstances at La Ñora were shared with most other small urban and rural areas. The sample was randomly selected but a participation bias cannot be ruled out since most of our participants expressed fear regarding BSs and this could contribute to their participation in the study. It is also possible to speculate that the percentage of participants who refused to participate did so for the opposite reasons (indifference about BSs). In this regard, neither health status nor subjective distance to the BS explained a willingness to participate in the study.

Concerns about radiation from BSs were not related to age, sex or subjective distance to BSs. This agrees with statements from several authors13 that living near a BS does not make people generally fearful, but people who generally worry about fields express stronger fears when they live close to a station.

Nevertheless, irrespective of these explanations, there seems to be effects of exposure that occur independently of the fear felt by the participants, since controlling for fear did not change the association between exposure and symptoms. However, the late query about concerns (as a possible confounder) may render the results less valid. In contrast to our findings, note that biological grounds explaining non-thermal effects have not been clearly established. Recently, it has been stated that voltage-gated calcium channels are essential to the beneficial or adverse responses to microwave EMFs, nanosecond EMF pulses and static electrical and magnetic fields.38

In summary, the results of this study indicate that effects of very low but long-lasting exposure to emissions from mobile telephone BSs on well-being cannot be ruled out. The effects almost completely matched the symptoms described within the microwave syndrome. Finally, unravelling the causal pathways would be best performed with an experimental study design.

Conclusions

This new study partially confirms our preliminary results about microwave sickness resulting from exposure to emissions from GSM mobile phone BSs. Fatigue, irritability, lack of appetite, sleep troubles, depression and lack of concentration were especially related with GSM exposure.

These results were independent of the main sociodemographic variables, other EMF exposures and anxiety about being irradiated. Nevertheless, we confirm that apprehension about modern technology could predict some symptoms, especially those related with sleep problems.

Our results agree with those who claimed that by distorting perceptions of risk, disproportionate precaution might paradoxically lead to illness that would not otherwise occur.39  However, health changes related with GSM exposure seem to occur in a manner unrelated with those fears. Finally, exposure was very low during the period and also very low in comparison with Spanish recommendations40 and international guidelines.41

Acknowledgments

The authors would like to express their gratitude to Angeles Martinez Gomez for her assistance during the fieldwork in La Ñora as well as to the Spanish Ministry of Science and Technology.

Footnotes

• Contributors CG-P was mainly responsible for designing and writing the manuscript and also made the main statistical contribution. EAN was one of the researchers responsible for the design and acquisition of radiofrequency electromagnetic field (RF EMF) data, as well as writing and reviewing the manuscript. JS contributed mainly in processing the RF EMF data, while MP was responsible for the design and final review of the manuscript.

• Funding This work was funded by the Spanish Ministry of Science and Technology for grant FIT number 070000-2002-58.

• Competing interests None.

• Patient consent Obtained.

• Ethics approval Ethical Committee of the University of Valencia in accordance with the Declaration of Helsinki (http://www.wma.net/e/policy/b3.htm).

• Provenance and peer review Not commissioned; externally peer reviewed.

• Data sharing statement The data used in this statistical analysis can be obtained from Dr CG-P on request by email (gomez_cla@gva.es).

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:http://creativecommons.org/licenses/by-nc/3.0/

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