Skip Navigation


American Journal of Epidemiology Advance Access originally published online on July 27, 2006
American Journal of Epidemiology 2006 164(6):538-548; doi:10.1093/aje/kwj247
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
164/6/538    most recent
kwj247v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (8)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Berg, G.
Right arrow Articles by Blettner, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Berg, G.
Right arrow Articles by Blettner, M.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

American Journal of Epidemiology Copyright © 2006 by the Johns Hopkins Bloomberg School of Public Health All rights reserved; printed in U.S.A.

Original Contribution

Occupational Exposure to Radio Frequency/Microwave Radiation and the Risk of Brain Tumors: Interphone Study Group, Germany

Gabriele Berg1, Jacob Spallek1, Joachim Schüz2,3, Brigitte Schlehofer4, Eva Böhler2,5, Klaus Schlaefer4, Iris Hettinger4, Katharina Kunna-Grass1, Jürgen Wahrendorf4 and Maria Blettner2

1 Department of Epidemiology and International Public Health, Faculty of Public Health, University of Bielefeld, Bielefeld, Germany
2 Institute of Medical Biostatistics, Epidemiology and Informatics, Johannes Gutenberg-University of Mainz, Mainz, Germany
3 Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark
4 Unit of Environmental Epidemiology, German Cancer Research Center, Heidelberg, Germany
5 Institute for Occupational, Social, and Environmental Medicine, University of Mainz, Mainz, Germany

Correspondence to Dr. Gabriele Berg, Department of Epidemiology and International Public Health, Faculty of Public Health, University of Bielefeld, P.O. 100131, 33501 Bielefeld, Germany (e-mail: gabriele.berg{at}uni-bielefeld.de).

Received for publication November 29, 2005. Accepted for publication March 7, 2006.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
It is still under debate whether occupational exposure to radio frequency/microwave electromagnetic fields (RF/MW-EMF) contributes to the development of brain tumors. This analysis examined the role of occupational RF/MW-EMF exposure in the risk of glioma and meningioma. A population-based, case-control study including 381 meningioma cases, 366 glioma cases, and 1,494 controls aged 30–69 years was performed in three German regions in 2000–2003. An exposure matrix for occupational activity was constructed by using information on RF/MW-EMF exposure collected in a computer-assisted personal interview. "High" exposure was defined as an occupational exposure that may exceed the RF/MW-EMF exposure limits for the general public recommended by the International Commission on Non-Ionizing Radiation Protection. Multiple conditional logistic regressions were performed separately for glioma and meningioma. No significant association between occupational exposure to RF/MW-EMF and brain tumors was found. For glioma, the adjusted odds ratio for highly exposed persons compared with persons not highly exposed was 1.21 (95% confidence interval: 0.69, 2.13); for meningioma, it was 1.34 (95% confidence interval: 0.64, 2.81). However, the slight increase in risk observed with increasing duration of exposure merits further research with larger sample sizes.

brain neoplasms; case-control studies; electromagnetic fields; occupations; radiation

Abbreviations: CI, confidence interval; RF/MW-EMF, radio frequency/microwave electromagnetic fields


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The question of whether occupational exposure to radio frequency/microwave electromagnetic fields (RF/MW-EMF) contributes to the development of brain tumors is still under debate. Interest in this specific frequency of RF/MW-EMF in the whole range of EMF, including extremely low frequency EMF or static fields, has risen, particularly because of cellular telephones. In 1988, Milham et al. (1Go) reported a nonsignificantly increased standardized mortality ratio of 1.39 (95 percent confidence interval (CI): 0.93, 2.00) for amateur radio operators. In subsequent years, several ad hoc analyses on this issue were published (2Go). As of now, seven cohort studies (1Go, 3Go–8Go) are known to have been published, but results are not consistent (table 1). A study of military personnel in Poland showed a significantly increased relative risk of several nervous system tumors, including brain cancer, in persons exposed to RF/MW-EMF (7Go). However, few details were given on the study methods used, and the increased risk of so many cancer types associated with radio frequency radiation has raised concerns about the validity of the results (9Go). In two case-control studies, a significant association between occupational exposure to RF/MW radiation and the risk of brain cancer was found (10Go, 11Go). One of these studies (10Go) even found a significant dose-response relation between duration of exposure and brain cancer risk. The other case-control study was nested in a cohort study of male members of the US Air Force. An increased risk for persons ever exposed to occupational RF/MW-EMF was reported, with an odds ratio of 1.39 (95 percent CI: 1.01, 1.90). However, there was no trend with either intensity of exposure or duration of exposure (11Go).


View this table:
[in this window]
[in a new window]

  		TABLE 1. Results of cohort studies and case-control studies of the association of occupational exposure and other activities to RF/MW-EMF* with the occurrence of brain tumors

 
None of these studies analyzed the association between occupational RF/MW-EMF and nonmalignant brain tumors. Experimental, up-to-date research provides no convincing evidence that low-level RF/MW-EMF exposure is involved in carcinogenesis. However, most of the discussion on the effect of RF/MW-EMF exposure refers to the hypothesis of a possible promoting effect of the exposure but not on the genetic mutation itself (12Go).

The aim of this analysis of the German part of the international Interphone Study was to investigate the association between RF/MW-EMF exposure and the risk of brain tumors in glioma and meningioma patients and in population controls. This paper focuses especially on occupational exposure to RF/MW-EMF, which was assessed by using information from a comprehensive personal interview including questions about job titles and specific occupational activities.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Study population
A population-based, case-control study (the German part of the international Interphone Study) was performed in line with the core protocol of the international Interphone Study (13Go). Incident meningioma and glioma cases aged 30–59 years (later extended to age 69 years) at the date of diagnoses were selected from four neurosurgical clinics located in Bielefeld, Heidelberg/Mannheim, and Mainz (covering some 6.6 million inhabitants). These four large clinics cover the metropolitan and rural areas surrounding these cities. Cases were eligible if their tumor was diagnosed between October 1, 2000, and October 31, 2003. On October 1, 2001, after receiving additional funding for the German part of the Interphone Study, the study was extended to include cases and controls aged 60–69 years at the date of diagnosis. Cases were all patients with histologically confirmed diagnoses of primary glioma or meningioma (benign or malignant) to ensure that no other brain tumors—for example, metastases, embryonic tumors, or tumors of the hemopoietic system—were included in the study. Therefore, 22 cases without histologic confirmation of their diagnosis were excluded. The following types of brain tumors (International Classification of Diseases for Oncology, Third Edition) were included for glioma: topography codes C71.0–C71.9 and morphology codes 9380–9383, 9390–9393, 9400–9401, 9410–9411, 9420–9421, 9424, 9440–9442, and 9450–9451. For meningioma, International Classification of Diseases for Oncology, Third Edition, topography code C70.0 and morphology codes 9530–9539 were included.

In total, 891 eligible patients were identified for the study. All were contacted by an interviewer after approval by the physician responsible for their treatment. The overall response rate for cases was 83.8 percent (n = 747) and was slightly lower for glioma patients (79.6 percent) than for meningioma cases (88.4 percent). For the analysis, data for 366 glioma patients and 381 meningioma patients were available. For glioma patients, the causes for not participating were death (n = 42), being too ill to answer the questions (n = 24), refusal (n = 22), or loss of contact after discharge from the hospital (n = 6). For some patients who were not able to answer, proxy interviews with relatives were performed (n = 40). The reasons for nonparticipation of meningioma patients were refusal (n = 21), being too ill to answer the questions (n = 16), loss of contact after discharge from the hospital (n = 9), and death (n = 4). Proxy interviews were performed for five meningioma cases.

A total of 2,449 eligible controls frequency matched to the cases by sex, age, and center were drawn from the compulsory population registries in the three regions. Participating in the study were 62.7 percent of them (n = 1,535). Contact by letter and telephone was made several times to improve the response rate. The reasons for nonparticipation in the study were refusal (n = 747), loss of contact (n = 118), being too ill (n = 48), and death (n = 1). At the end of the data collection phase, a post hoc 1:2-person matching was performed by assigning two controls to each case matched by sex, birth year (±2 years), and region (Bielefeld, Heidelberg/Mannheim, Mainz; few exceptions) to adjust for the time lag in interviewing cases and controls. By using this method, the exposure period for the controls was censored at the date of diagnosis of the matched case. Two corresponding controls were matched to each case. For the analyses, data for 732 individually matched controls for the 366 glioma cases and 762 controls for the 381 meningioma cases were available. More details on the materials and methods are published elsewhere (14Go).

Data collection
Computer-assisted personal interviews were conducted by trained interviewers and included questions on demographic characteristics; use of cellular telephones, transmitters, and ham radios; smoking and medical histories; diagnostic treatment; and occupational activities related to EMF and ionizing radiation. Most cases were interviewed during their stay in the hospital or, if this option was not possible, at home, after their surgery. The controls were mostly interviewed at home. Each interviewer questioned cases as well as controls. The duration of the interview was compared between cases and controls. Mean duration was 52.0 minutes for controls (standard deviation, 18.9) and 55.1 minutes for cases (standard deviation, 19.7). At the beginning of the study, the computer-assisted personal interview was not available. Therefore, a printed version was used for the first 7 months for interviews with 122 cases and 202 controls. However, unlike the computer-assisted personal interviews, the printed version did not include all details of occupational history. For these first 7 months, only so-called screening questions on occupational history were asked. Persons who reported any of the activities listed in these screening questions were approached later for a more detailed telephone interview when the computer program was available. Sensitivity analyses were performed to test for differences in the results by data collection method.

Occupational exposure assessment
A detailed questionnaire on occupational activities related to RF/MW-EMF and the whole range of EMF, including static fields and very low frequency EMF, as well as ionizing radiation, was constructed by the International Exposure Assessment Committee of the Interphone Study. In this analysis, only RF/MW-EMF details were assessed. Information on the following occupational activities was derived from this questionnaire; screening questions about possible activities with RF/MW-EMF exposure asked about 1) using industrial heating equipment to process food; to bond, seal, and weld materials; or to melt, dry, and cure materials; 2) manufacturing semiconductor chips or microelectronic devices; 3) using radar; 4) maintaining electromagnetic devices used to treat or diagnose diseases; 5) working with or nearby broadcasting and telecommunications antennae and masts; 6) using different kinds of transmitters; and 7) using a ham radio. The following screening questions were not considered because the activities mentioned were not related to RF/MW-EMF exposure: 1) working next to electrical motors; 2) being employed by an electric company; 3) working directly on or around any electric transport; 4) constructing, maintaining, or repairing electrical machinery or equipment; 5) using industrial machinery powered by electric motors; 6) using other electrical equipment not mentioned before; 7) working with ionizing radiation; and 8) being employed as an airline pilot or crew member.

Occupations associated with the following frequency ranges were considered: radio transmission (30–300 MHz); cellular and personal communication, including ham radio use (800 MHz–2GHz); and industrial applications such as microwave heating and medical applications, and rarely for ham radio use (up to 2.45 GHz) (15Go). Because of the small numbers of observations, we included all frequency ranges in one exposure category. However, most of the considered exposures were related to personal communication devices (800 MHz–2 GHz).

The following procedure was used to estimate exposure to RF/MW-EMF. First, all persons who marked one of the activities listed in the above-mentioned screening questions were selected.

Second, all activities mentioned by at least one person were classified with regard to possible exposure to RF/MW-EMF. The computer-assisted personal interviews included some detailed questions to determine whether the occupation led to a measurable exposure to RF/MW-EMF. All activities were classified into four categories based on the scientific literature (16Go–26Go) as well as on a review by two German industrial hygienists. Some occupational activities mentioned in these screening questions were categorized as "no RF/MW-EMF" exposure. Examples included a physician working with an electrocardiogram, a cook working in a kitchen, all types of metal welding, and binding and gluing plastic and nylon without microwave heating.

The remaining activities were classified according to the degree or the likelihood of exposure. If the exposure existed and was probably present continuously during the mentioned working hours, the activity was categorized as "probable" exposure. If the exposure surely existed continuously during the mentioned working hours and sometimes exceeded 0.08 W/kg (which corresponds to the exposure limits of RF/MW-EMF for the general population (27Go)), this activity was categorized as "high" exposure. The International Commission on Non-Ionizing Radiation Protection guidelines allow these exposure limits for the general public to be exceeded by a factor of five for occupational exposures (27Go). A certain exposure that did not exceed the general exposure limits was considered a probable exposure because it occurred only rarely. Finally, activities were grouped as "not probable" when the activity mentioned was related to RF/MW-EMF but it was presumed that the person was not exposed to RF/MW-EMF. For example, the use of a transmitter inside a car was regarded as an exposure to RF/MW-EMF only when it was mentioned that the transmitter antenna was located inside the car.

Third, the different activities were grouped together for each person, and duration of exposure in each summarized category was calculated. For example, a person who worked from 1980 to 1989 in an RF/MW-EMF exposed job categorized as probable exposure and from 1990 to 1995 in an RF/MW-EMF exposed job categorized as high exposure was considered RF/MW-EMF exposed for 15 years, including 5 years with high RF/MW-EMF exposure. Only those activities up to 2 years prior to the date of diagnosis of the tumor or the reference date for controls, respectively, were taken into account.

A description of probable and high exposure activities is presented in table 2, and a flow chart of the exposure categorization used is shown in figure 1. The activities were categorized without knowledge of the disease status of the participant. The activity exposure matrix includes 277 activities; among those, 130 are classified as high exposure, 147 as probable exposure, and 212 as not probable exposure.


View this table:
[in this window]
[in a new window]

  		TABLE 2. Job activities and their grouping according to intensity of RF/MW-EMF* exposure, German Interphone Study (Bielefeld, Heidelberg/Mannheim, and Mainz), 2000–2003

 

Figure 1
View larger version (18K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		FIGURE 1. Flow chart of the structure of the exposure matrix for specific activities involved in occupations. Data were derived from the German Interphone Study (Bielefeld, Heidelberg/Mannheim, and Mainz), 2000–2003. Boxes with solid lines indicate individual data, boxes with broken lines indicate data based on each mentioned activity. RF/MW-EMF, radiofrequency/microwave electromagnetic fields.

 
Statistical analysis
Conditional logistic regression was performed to account for frequency matching by using SAS software (version 9.1; SAS Institute, Inc., Cary, North Carolina). All regression models were stratified for the three regions and for sex. Adjusting variables were socioeconomic status, urban (≥100,000 inhabitants) vs. rural (<100,000 inhabitants) area, corresponding age at diagnosis, smoking history, and ionizing radiation exposure. Socioeconomic status was based on educational and occupational training in Germany, yielding three levels. Smoking history was considered current smoker, former smoker, or nonsmoker. Ionizing radiation was categorized into four groups: (0) no exposure; (1) at least five lifelong radiographic examinations but no computed tomography (excluding radiographic examinations of a single tooth); (2) more than five radiographic examinations or at least one computed tomography, angiography, and/or szintigraphy; and (3) occupational exposure to ionizing radiation for at least 5 years, or any radiation therapy. Only those examinations considering the head and neck were included. The use of cellular telephones was not deemed a confounder. Sensitivity analyses were performed to consider the use of cellular telephones as a confounder. However, the results were very similar to those presented here and are therefore not shown. Occupational exposure was analyzed with three different models:
  1. Model 1: any RF/MW-EMF exposure (no/yes).
  2. Model 2: four categories—no exposure, not probable, probable, and high.
  3. Model 3: three categories considering duration of exposure—no high exposure (including no exposure, not probable, and probable), less than 10 years of high exposure, and 10 or more years of high exposure. The category of high exposure was introduced to increase sensitivity by taking into account duration of exposure. All other potential exposure categories were considered not exposed because they do not exceed the exposure limits for the general population. By doing so, a potential threshold above the limits of the general population was examined.

The analyses were repeated after excluding data from proxy interviews. The results were very similar to those presented here and are therefore not shown. Sensitivity analyses were conducted after excluding persons for whom the full computerized personal interview was impossible. For gliomas, the results were very similar to those presented here. For meningioma, possibly because of small numbers, differences within the random variation of the results were found.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
The distribution of major characteristics of the study population is presented in table 3. The median age was 53 years for glioma cases and 55 years for meningioma cases and did not differ between cases and controls. Nearly 60 percent of glioma cases were male, whereas only 27 percent of meningioma cases were male. Compared with that for cases, socioeconomic status of controls in both diagnostic groups was slightly higher. Most of the cases and controls were recruited from urban areas.


View this table:
[in this window]
[in a new window]

  		TABLE 3. Description of the study population, German Interphone Study (Bielefeld, Heidelberg/Mannheim, and Mainz), 2000–2003

 
Overall, 104 persons were considered probably exposed to RF/MW-EMF and 87 as highly exposed. The results of the crude and adjusted conditional logistic regressions are presented in table 4 for glioma and in table 5 for meningioma. RF/MW-EMF exposure was not associated with occurrence of glioma or meningioma in the total study population. For glioma (table 4), the adjusted odds ratio was 1.04 (95 percent CI: 0.68, 1.61). However, when we included duration of RF/MW-EMF exposure and focused solely on high exposure, the odds ratios for gliomas increased slightly. For persons who worked less than 10 years, the adjusted odds ratio for high exposure compared with not high exposure was 1.11 (95 percent CI: 0.48, 2.56); for persons who worked 10 years or more, the corresponding odds ratio was 1.39 (95 percent CI: 0.67, 2.88).


View this table:
[in this window]
[in a new window]

  		TABLE 4. Crude odds ratios and odds ratios from multiple conditional logistic regressions for the association of RF/MW-EMF* exposure with glioma, German Interphone Study (Bielefeld, Heidelberg/Mannheim, and Mainz), 2000–2003

 

View this table:
[in this window]
[in a new window]

  		TABLE 5. Crude odds ratio and odds ratio from multiple conditional logistic regressions of the association of RF/MW-EMF* exposure with meningioma, German Interphone Study (Bielefeld, Heidelberg/Mannheim, and Mainz), 2000–2003

 
The results of the conditional logistic regressions with regard to the association between RF/MW-EMF exposure and occurrence of meningioma were similar (table 5). The adjusted odds ratio for exposure to RF/MW-EMF was 1.12 (95 percent CI: 0.66, 1.87). The adjusted odds ratios for high exposure compared with not high exposure were 1.14 (95 percent CI: 0.37, 3.48) for an exposure of less than 10 years and 1.55 (95 percent CI: 0.52, 4.62) for an exposure of 10 years or more.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
To our knowledge, our case-control study is the first in which exposure to RF/MW-EMF has been investigated among a large number of persons by using a detailed interview on occupational history and particular job activities. No significant association between occupational exposure to RF/MW-EMF and brain tumors was found in the data from the German part of the Interphone case-control study. A slightly increased risk was observed for high exposure in comparison with probable exposure as well as an increasing odds ratio with increasing duration of years in high-exposure jobs. However, this result should be interpreted with caution, particular because of the small number of exposed persons.

Our results resemble those from the other case-control studies analyzing the association between RF/MW-EMF exposure and development of brain tumors. Thomas et al. (10Go) found an odds ratio of 1.6 (95 percent CI: 1.0, 2.4) for persons ever exposed to occupational RF radiation and a significant dose-response association between years of working and brain cancer death. Grayson (11Go) analyzed persons ever exposed to occupational RF/MW-EMF and found an odds ratio of 1.39 (95 percent CI: 1.01, 1.90). However, in contrast to our results, a dose response, in this study measured by a potential exposure score, was not found in that study (11Go). Five cohort studies revealed no association between occupational RF/MW-EMF exposure and the occurrence of brain tumors (3Go–6Go, 8Go). For amateur radio operators, a nonsignificant standardized mortality ratio of 1.39 (95 percent CI: 0.93, 2.00) was found (1Go). However, there is currently little evidence from cellular and animal studies of the carcinogenicity of RF/MW-EMF (15Go).

Measurement of RF/MW-EMF exposure was subject to some methodological discussion; cohort studies that are analyzing a large number of persons acknowledge the difficulty in identifying actually exposed persons rather than occupational groups (28Go). Thus, no data on individual shielding systems and day-to-day duration of individual exposure were available. This limitation might have led to an exposure classification with high specificity but low sensitivity. This type of nondifferential misclassification in dichotomous exposure assessment is associated mostly with an outcome measure biased toward the null effect (29Go). The older case-control study (10Go) used two methods of classifying RF/MW-EMF: first, subjects' occupational history was assigned a three-digit code for industry and a census code for occupations; second, each job listed in the occupational history was categorized by a certified industrial hygienist as high, moderate, or low. In the nested case-control study performed among the US Air Force population, a subgroup of persons exposed to RF/MW-EMF above permissible exposure limits (10 mW/cm2) was identified by a historical list of incidents. All other job titles were assigned to the nonexposed category (11Go).

Our assessment of occupational exposure was based on individual activities during employment instead of job titles. Doing so enabled us to consider individual exposure to RF/MW-EMF and the use of shielding systems. In particular, the category of high-exposure activities derived from the comprehensive questionnaire was established to consider the specific exposure situation during an activity. This method was used to allow a more sensitive exposure estimation of the real situation and a more specific exclusion of a nonexposure situation during a possible-exposed occupation.

This study has some limitations, which is common in case-control studies. First, recall bias may have been present, particularly because of the extensive questionnaire used. It might be that cases, because of their preoccupation with disease, overestimated their exposure compared with that of controls (recall bias type A). It could also happen that, because of their disease, cases were unable to answer accurately (recall bias type B). Recall bias A might lead to an overestimation of occupational exposure and should be particularly obvious in occupational screening questions. However, because we constructed the activity exposure matrix from given information in the computer-assisted personal interviews, participants did not know which answer was used to determine RF/MW-EMF exposure. Thus, in the high RF/MW-EMF exposed group, recall bias A is unlikely. Recall bias B was also analyzed by performing a sensitivity analysis for all interviews, excluding proxy interviews. As mentioned above, the results for both analyses did not differ. The potential impact of selection bias also needs to be discussed in case-control studies. The response rate differed between cases (83.8 percent) and controls (62.4 percent). Selection bias related to exposure to occupational RF/MW-EMF may not be as obvious in this analysis of the Interphone Study as it is for the exposure in connection with cellular phone use. Analysis of a short nonresponder questionnaire showed that male, but not female, controls were more likely to refrain from regular cellular phone use as well as to refuse to participate in this study (14Go).

The number of observed cases in cohort studies of RF/MW-EMF exposure is small because brain tumors are rare (table 1). Until now, the number of cases included in this case-control study (366 glioma cases and 381 meningioma cases) is the highest of all published case-control studies investigating occupational RF/MW-EMF exposure. Nevertheless, the number of people with high exposure among cases and controls identified is still small (22 glioma cases and 11 meningioma cases). Hence, there might not be enough statistical power to find a possible small risk, particularly for patients with a long duration of exposure.

All frequency ranges of RF/MW-EMF were included in one exposure category. In the high-exposure group, 114 of 130 activities (table 2: area transmitter) occurred in the context of personal communication devices representing the frequency range of 800 MHz–2 GHz (15Go). To our knowledge, there is no different etiologic mechanism in discussions of the different frequency ranges of RF/MW-EMF and the stated promoting effect on tumors. Furthermore, in the group with high exposure, we considered the limit among the general public recommended by the International Commission on Non-Ionizing Radiation Protection. These limits are equal for all considered frequency ranges (specific absorption rate of 0.08 W/kg) and are based on the established thermal effect in all of these RF/MW-EMF frequency ranges (27Go).

To our knowledge, this is the first time that the association between RF/MW-EMF exposure and nonmalignant brain tumors such as meningioma has been considered. The results for meningiomas and gliomas were virtually identical. Meningiomas and gliomas are of different tissue origin; meningiomas arise from meningothelia cells, whereas gliomas arise from glial cells. Compared with gliomas, meningiomas might be associated with a longer latency period. Up to now, no previously published study has been known to show an association between RF/MW-EMF exposure from cellular phone use and meningioma. Positive associations with glioma have been reported in two of six studies, but methodological considerations limited interpretability of the findings (30Go). Therefore, the similar association we found for long-duration exposure among highly exposed participants concerning both brain tumor types and the exposure of RF/MW-EMF found in our analysis should be discussed. The stated tumor-promoting effect of RF/MW-EMF might be the same for meningiomas and gliomas. In our study, the high-exposure category was defined so we could look for a potential effect of an RF/MW-EMF exposure above the exposure limits for the general population. Although doing so may strengthen the plausibility of the results, it leads to the effect that only a few persons are regarded as "exposed." Furthermore, it cannot be excluded whether potential information bias or selection bias could lead to a similar increase in risk of both brain tumor entities. For confirmation of these results, further analysis of the pooled Interphone data set is awaited.

This study shows the first known results concerning exposure to RF/MW-EMF in the frame of occupational activities and occurrence of glioma and meningioma. We did not find a significant association between occupational exposure to RF/MW-EMF and brain tumors, but odds ratios for both glioma and meningioma were slightly increased for long-duration and high exposure. These results were based on low numbers of exposed participants and need be confirmed by the results of the pooled analyses of the Interphone Study. In a larger data set, it will also be possible to perform a stratified analysis of different types of brain tumors such as high-grade or low-grade gliomas, of gender, of different exposure estimates for activities associated with particular RF/MW-EMF frequency ranges, and of a higher number of expected long-term RF/MW-EMF exposed workers.


   ACKNOWLEDGMENTS
 
The authors acknowledge funding from the European Fifth Framework Program, "Quality of Life and Management of Living Resources" (contract QLK4-CT-19999-01563); the "Deutsches Mobilfunkforschungsprogramm" of the German Federal Ministry for the Environment, Nuclear Safety, and Nature Protection; the Ministry for the Environment and Traffic of the state of Baden-Württemberg; the Ministry for the Environment of the state of North Rhine-Westphalia; the MAIFOR Program of the University of Mainz; and the International Union against Cancer (UICC). The UICC received funds for this purpose from the Mobile Manufacturers' Forum and GSM Association. Provision of funds to the Interphone Study investigators via the UICC was governed by agreements that guaranteed Interphone's complete scientific independence. These agreements are publicly available at the following website: http://www.iarc.fr/pageroot/UNITS/RCA4.html (accessed July 1, 2005).

The authors thank Dr. Hauke Brüggemeyer of the Lower Saxony State Agency for Ecology and Markus Fischer from the Professional Association for Safety and Health at Work (BFGA) for their scientific support in building the activity exposure matrix. They also thank Marianne Brömmel, Stephanie Estel, Melanie Hetzer, and Anna Wilms for organizing the field phase and all of the interviewers for their skillful work. The authors thank the clinical Interphone Study team for their support and collaboration: Bielefeld: Prof. Falk Oppel (Neurosurgical clinic), Dr. Uwe Dietrich (Neuroradiology), and Dr. Volkmar Hans (Neuropathology); Heidelberg: Prof. Andreas Unterberg, Prof. Stefan Kunze, Dr. Karsten Geletneky (Neurosurgical clinic), and Prof. Marika Kiessling (Neuropathology); Mannheim: Prof. Peter Schmiedek, Dr. Jochen Tüttenberg (Neurosurgical clinic), and Prof. Uwe Bleyl (Neuropathology); Mainz: Prof. Axel Perneczky, Prof. Nico Hopf, Dr. Dorothee Koch (Neurosurgical clinic), Prof. Wolf Mann, Prof. Nickalaos Marangos (ENT clinic), Dr. Wibke Müller-Forell (Neuroradiology), and Prof. Hans Hilmar Göbel (Neuropathology). They also thank the coordination team at the International Agency for Research on Cancer in Lyon, Switzerland, for their support.

Conflict of interest: none declared.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Milham S Jr. Increased mortality in amateur radio operators due to lymphatic and hematopoietic malignancies. Am J Epidemiol 1988;127:50–4.[Abstract/Free Full Text]
  2. Blettner M, Schlehofer B. Is there a high risk for leukemia, brain tumor or breast cancer during the exposure of high frequency radiation? (In German). Med Klin 1999;94:150–9.[Medline]
  3. Groves FD, Page WF, Gridley G, et al. Cancer in Korean War Navy technicians: mortality survey after 40 years. Am J Epidemiol 2002;155:810–18.[Abstract/Free Full Text]
  4. Morgan RW, Kelsh MA, Zhao K, et al. Radio frequency exposure and mortality from cancer of the brain and lymphatic/hematopoietic systems. Epidemiology 2000;11:118–27.[CrossRef][Web of Science][Medline]
  5. Finkelstein MM. Cancer incidence among Ontario police officers. Am J Ind Med 1998;34:157–62.[CrossRef][Web of Science][Medline]
  6. Tynes T, Andersen A, Langmark F. Incidence of cancer in Norwegian workers potentially exposed to electromagnetic fields. Am J Epidemiol 1992;136:81–8.[Abstract/Free Full Text]
  7. Szmigielski S. Cancer mortality in subjects occupationally exposed to high-frequency (radio frequency and microwaves) electromagnetic radiation. Sci Total Environ 1996;180:9–17.[CrossRef][Medline]
  8. Tynes T, Hannevik M, Andersen A, et al. Incidence of breast cancer in Norwegian female radio and telegraph operators. Cancer Causes Control 1996;7:197–204.[CrossRef][Web of Science][Medline]
  9. Elwood JM. A critical review of epidemiologic studies of radiofrequency exposure and human cancers. Environ Health Perspect 1999;107(suppl 1):155–68.
  10. Thomas TL, Stolley PD, Stemhagen A, et al. Brain tumor mortality risk among men with electrical and electronic jobs: a case control-study. J Natl Cancer Inst 1987;79:233–8.[Web of Science][Medline]
  11. Grayson JK. Radiation exposure, socioeconomic status, and brain tumor risk in the US Air Force: a nested case control study. Am J Epidemiol 1996;143:480–6.[Abstract/Free Full Text]
  12. IEGMP. Steward W, chairman. Mobile phones and health. Report of an Independent Expert Group on Mobile Phones. Chilton, United Kingdom: National Radiological Protection Board, 2000.
  13. Cardis E, Kilkenny M. International case-control study of adult brain, head and neck tumours: results of the feasibility study. Radiat Prot Dosimetry 1999;83:179–83.[Abstract]
  14. Schüz J, Böhler E, Berg G, et al. Cellular phones, cordless phones, and the risk of gliomas and meningiomas in Germany. Am J Epidemiol 2006;163:512–20.[Abstract/Free Full Text]
  15. Habash RWY, Brodsky LM, Leiss W, et al. Health risks of electromagnetic fields. Part II: evaluation and assessment of radiofrequency radiation. Crit Rev Biomed Eng 2003;31:197–254.[CrossRef][Medline]
  16. National Radiological Protection Board (NRPB). Health effects from radiofrequency electromagnetic fields. London, United Kingdom: NRPB, 2003. (Documents of the NRPB: vol 14, no. 2).
  17. Bundesamt für Umwelt, Wald und Landschaft (UWAL). High frequency radiation and health. (In German). Umwelt-Materialien Bern: Nichtionisierende Strahlung, 2003:162.
  18. Floderus B, Stenlund C, Carlgren F. Occupational exposures to high frequency electromagnetic fields in the intermediate range (>300 Hz–10 MHz). Bioelectromagnetics 2002;23:568–77.[CrossRef][Web of Science][Medline]
  19. Fachverband für Strahlenschutz e V (FVSS): Brüggemeyer H, Eichhorn KF, Eggert S, et al: Leitfaden. Guide: nonionizing radiation. (In German). Elektromagnetische Felder, 1999. (FS 07-90-AKNIR Köln).
  20. Richter E, Berman T, Ben Michael E, et al. Cancer in radar technicians exposed to radiofrequency/microwave radiation: sentinel episodes. Int J Occup Environ Health 2000;6:187–93.[Medline]
  21. Minister of Public Works and Government Services (MPWGS). Limits of human exposure to radiofrequency electromagnetic fields in the frequency range from 3 kHz to 300 GHz—safety code 6. Ottawa, Canada: MPWGS, 1999.
  22. Allgemeine Unfallversicherungsanstalt (AUVA). Measurement and safety related evaluation of electromagnetic fields in induction furnace. (In German). 1998: Report (2).
  23. Allgemeine Unfallversicherungsanstalt (AUVA). Analysis of workplaces in high frequency radiation. (In German). 1998: Report (1).
  24. Bundesministerium für Gesundheit und Konsumentenschutz (BGK). Study on documented research results about the effect of electromagnetic fields. (In German). 1997; (2): Hochfrequente elektromagnetische Felder.
  25. Brüggemeyer H. Electric and magnetic fields on workplaces with high frequency plastic welding machines. (In German). Niedersächsisches Sozialministerium, Landesamt für Ökologie Hannover, 1996.
  26. National Council on Radiation Protection and Measurements (NCRP). A practical guide to the determination of human exposure to radiofrequency fields. Bethesda, MD: NCRP, 1993.
  27. Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz). International Commission on Non-Ionizing Radiation Protection. Health Phys 1998;74:494–522.[Web of Science][Medline]
  28. Breckenkamp J, Berg G, Blettner M. Biological effects on human health due to radiofrequency/microwave exposure: a synopsis of cohort studies. Radiat Environ Biophys 2003;42:141–54.[CrossRef][Web of Science][Medline]
  29. Brenner H, Savitz DA, Gefeller O. The effects of joint misclassification of exposure and disease on epidemiologic measures of association. J Clin Epidemiol 1993;46:1195–202.[CrossRef][Web of Science][Medline]
  30. Lönn S, Ahlbom A, Hall P, et al. Long-term mobile phone use and brain tumor risk. Am J Epidemiol 2005;161:526–35.[Abstract/Free Full Text]

Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
164/6/538    most recent
kwj247v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (8)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Berg, G.
Right arrow Articles by Blettner, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Berg, G.
Right arrow Articles by Blettner, M.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?