Occupational exposure to high-frequency electromagnetic fields and brain tumor risk in the INTEROCC study: An individualized assessment approach

Abstract

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.

Keywords: Brain cancer; EMF; Intermediate frequency; Radiofrequency; Source-exposure matrix; Workers.

Figure 1.

Cumulative exposure to radiofrequency (RF) and intermediate frequency (IF) electric and magnetic fields (various metrics) by brain tumour type and exposure lag (overall exposure, 1-year lag) and time window (1–4 years exposure time window). Status (1=Cases; 0=Controls).

Figure 2.

Exposure-response relationship between risk of glioma and meningioma (ORs based on conditional logistic regression models, matched by 5-year age group, sex, country, and region, and adjusted by education) and RF E-field cumulative exposure (ICNIRP ratio²-years) for overall exposure (1-year lag) and 1- to 4-year exposure time window. The dashed lines indicate the linear model (black line) and a quadratic model with log-transformed exposure (yellow line). The grey shadow indicates Wald-type 95% CIs for the linear model. Vertical dashed lines on the left side of the plot indicate the cut points used in the categorical analysis (i.e. 50^th, 75^th and 90^th percentiles of the cumulative exposure distribution of controls). Points and error bars indicate adjusted ORs and Wald-type 95% CIs for the exposure categories based on these cut points. The ORs and CIs from the categorical analysis are positioned at the median exposure for each interval. Plot rug are cases (dashed short vertical black lines) and controls (dashed short vertical grey lines). Plots truncated at the 95^th percentile of cumulative exposure to improve visibility.