Abstract and Introduction

Abstract

We investigated the association between exposure to radio-frequency electromagnetic fields (RF-EMFs) from broadcast transmitters and childhood cancer. First, we conducted a time-to-event analysis including children under age 16 years living in Switzerland on December 5, 2000. Follow-up lasted until December 31, 2008. Second, all children living in Switzerland for some time between 1985 and 2008 were included in an incidence density cohort. RF-EMF exposure from broadcast transmitters was modeled. Based on 997 cancer cases, adjusted hazard ratios in the time-to-event analysis for the highest exposure category (>0.2 V/m) as compared with the reference category (<0.05 V/m) were 1.03 (95% confidence interval (CI): 0.74, 1.43) for all cancers, 0.55 (95% CI: 0.26, 1.19) for childhood leukemia, and 1.68 (95% CI: 0.98, 2.91) for childhood central nervous system (CNS) tumors. Results of the incidence density analysis, based on 4,246 cancer cases, were similar for all types of cancer and leukemia but did not indicate a CNS tumor risk (incidence rate ratio = 1.03, 95% CI: 0.73, 1.46). This large census-based cohort study did not suggest an association between predicted RF-EMF exposure from broadcasting and childhood leukemia. Results for CNS tumors were less consistent, but the most comprehensive analysis did not suggest an association.

Introduction

Radio-frequency electromagnetic fields (RF-EMFs) from broadcast transmitters (radio and television transmitters) have been hypothesized to cause childhood cancer, although a biological mechanism has not been identified for low exposure levels.[1,2] The International Agency for Research on Cancer (IARC) has classified RF-EMFs as "possibly carcinogenic to humans (group 2B)" based on positive associations between glioma and acoustic neuroma and exposure to RF-EMFs from wireless telephones.[3] Regarding studies on the possible association between cancer and exposure to RF-EMFs from fixed-site transmitters, the IARC Working Group found the available evidence insufficient to draw a conclusion.

The output power of broadcast transmitters can be high, in order to cover large geographical areas. Thus, they are spaced far apart, and field levels can be relatively high in the immediate vicinity at ground level. As a consequence, epidemiologic exposure assessment for these sources is less vulnerable to exposure misclassification than that for other environmental RF-EMF sources such as mobile-phone base stations, which display a much higher spatial variation.[4,5] High spatial heterogeneity is a challenge for modeling but also for exposure assignment, because children are not stationary at their place of residence.

Most previous studies on this topic used an ecological design, and leukemia rates were mostly found to be increased in the proximity of broadcast transmitters, reaching statistical significance in some[6–9] but not all[10–12] studies. However, lack of individual exposure data and lack of confounding adjustment limits interpretation. Further, some of these ecological studies were based on small sample sizes and were initiated because of previous cluster reports. Recently, the results of 2 more informative large case-control studies with individual exposure assessment based on modeling were published.[13–15] A South Korean study[13,14] with 1,928 childhood leukemia cases and an equal number of matched hospital-based controls found no association between childhood leukemia risk and the average predicted field strengths from 31 amplitude-modulation (AM) radio transmitters. However, children living within 2 km of the transmitters had a relative risk of 2.15 (95% confidence interval (CI): 1.00, 4.67) for all types of leukemia compared with children living more than 20 km away. The other large case-control study,[15] conducted in the vicinity of 16 AM and 8 frequency-modulation (FM) broadcast transmitters in Germany, included 1,959 leukemia cases and 3 population-based controls per case, matched on age, sex, and transmitter area. That study found no indication for an association between RF-EMFs and childhood leukemia.

The aim of our study was to investigate, within a prospective, census-based cohort study design, the association between RF-EMF exposure from broadcast transmitters and childhood cancer, particularly leukemia and tumors of the central nervous system (CNS).