No clear associations were found between occupational exposure to high frequency electromagnetic fields (EMF) and risk of glioma or meningioma, in one of the largest epidemiological studies performed to date and led by ISGlobal, an institution supported by “la Caixa” Foundation. However, the findings highlight the need for further research on radiofrequency magnetic fields and tumour promotion, as well as possible interactions with other frequencies and with chemicals.
High frequency electromagnetic fields are a form of non-ionising radiation and comprise intermediate frequency (3kHz-10MHz) and radiofrequency (10MHz-300 GHz). Based on limited animal and epidemiological evidence, they were declared by the World Health Organisation’s (WHO’s) International Agency for Research on Cancer (IARC) in 2011 as possibly carcinogenic to humans, but few recent studies have provided further evidence regarding exposure at work. “This is the largest study of brain tumours and occupational high-frequency EMF exposure to date,” explains senior author Elisabeth Cardis, head of the radiation programme at ISGlobal.
The researchers developed a “source-exposure matrix” based on measurements collected from the literature for EMF sources reported by the study participants. With this tool plus detailed individual data, they estimated individual RF and IF exposure at work and analysed the possible association with risk of glioma or meningioma, two of the most frequent brain tumours in adults.
The INTEROCC study, performed under the umbrella of INTERPHONE, and supported by the European project GERoNiMO, comprised 2,054 glioma cases, 1,924 meningioma cases and 5,601 controls from seven countries. Occupational sectors that involved exposure to electromagnetic fields included working with or near radars, telecommunication antennas, medical diagnosis and treatment and microwave drying ovens, among others.
Despite the major improvements in estimating exposure, this large case-control study provided no clear evidence for a positive association between cumulative high-frequency EMF exposure and glioma or meningioma risk. However, the number of exposed participants was small: only 10% of the participants were exposed to radiofrequencies and less than 1% were exposed to intermediate frequencies, which limited the statistical power to find clear associations, if they exist.
“Our individualised exposure assessment approach is an important improvement over previous efforts to assess high-frequency EMF exposure risks. Although we did not find a positive association, the fact that we observed indication of an increased risk in the group with most recent radiofrequency exposure deserves further investigation,” explains first author Javier Vila. “We also need to investigate possible interactions with other frequencies, and with chemicals,” adds Cardis.
Introduction: In 2011, the International Agency for Research on Cancer classified radiofrequency (RF) electromagnetic fields (EMF) as possibly carcinogenic to humans (group 2B), although the epidemiological evidence for the association between occupational exposure to RF-EMF and cancer was judged to be inadequate, due in part to limitations in exposure assessment. This study examines the relation between occupational RF and intermediate frequency (IF) EMF exposure and brain tumor (glioma and meningioma) risk in the INTEROCC multinational population-based case-control study (with nearly 4000 cases and over 5000 controls), using a novel exposure assessment approach.
Methods: Individual indices of cumulative exposure to RF and IF-EMF (overall and in specific exposure time windows) were assigned to study participants using a source-exposure matrix and detailed interview data on work with or nearby EMF sources. Conditional logistic regression was used to investigate associations with glioma and meningioma risk.
Results: Overall, around 10% of study participants were exposed to RF while only 1% were exposed to IF-EMF. There was no clear evidence for a positive association between RF or IF-EMF and the brain tumors studied, with most results showing either no association or odds ratios (ORs) below 1.0. The largest adjusted ORs were obtained for cumulative exposure to RF magnetic fields (as A/m-years) in the highest exposed category (≥90th percentile) for the most recent exposure time window (1–4 years before the diagnosis or reference date) for both glioma, OR = 1.62 (95% confidence interval (CI): 0.86, 3.01) and meningioma (OR = 1.52, 95% CI: 0.65, 3.55).
Conclusion; Despite the improved exposure assessment approach used in this study, no clear associations were identified. However, the results obtained for recent exposure to RF electric and magnetic fields are suggestive of a potential role in brain tumor promotion/progression and should be further investigated.
Javier Vila, Michelle C Turner, Esther Gracia-Lavedan, Jordi Figuerola, Joseph D Bowman, Laurel Kincl, Lesley Richardson, Geza Benke, Martine Hours, Daniel Krewski, Dave McLean, Marie-Elise Parent, Siegal Sadetzki, Klaus Schlaefer, Brigitte Schlehofer, Joachim Schüz, Jack Siemiatycki, Martie van Tongeren, Elisabeth Cardis