Use of Mobile Phones and Brain Cancer Risk in Children?

Fig. 29.1

Overview about the electromagnetic spectrum

In addition to mobile phones many other wireless communication devices emit RF-EMF, such as W-LANs (wireless local area networks), cordless phones or broadcast transmitters. Thus, the question arises how relevant is brain exposure from mobile phones compared to exposures from other sources. The absorbed energy of the body depends mainly on the source strengths and the distance to the source. Mobile phones are relatively strong transmitters since they have to reach longer distances than other daily RF-EMF sources (e.g., W-LAN, cordless phones). Obviously, fixed site transmitters used for broadcasting or mobile communication have a stronger output power than mobile phones. However, distance to the receiver is considerable larger than for mobile phone handsets which operates close to the body. In general, the SAR decreases with the square of the distance to the source, although the situation can be much more complex close to the source. For example, if the SAR value for a mobile phone is 1.0 W/kg at a distance of 0.5 cm from the head, this value would decrease by approximately a factor of 64 (=0.016 W/kg) at a distance of 4 cm. As a consequence, for a person who is using a mobile phone for at least a minute per day, the far largest exposure contribution to the brain is arising from the use of mobile phones when holding it to the head. Exposures from cordless phones are also relevant, because these devices are held to the head as well; the emitted power was lower compared to the second generation of mobile phones (Global System for Mobile Communications), but may be equally important in terms of exposure assessment compared to the UMTS (Universal Mobile Telecommunications System) mobile phone technology (Gati et al. 2009). Currently, the fourth generation (LTE: Long Term Evolution) is implemented. Preliminary measurements suggest that exposure levels of handsets will be comparable with the second generation of mobile phones. The exposure contributions from all other sources in the everyday environment are negligible for the brain (Frei et al. 2009). And there is neither any other part of the body which is exposed to any other sources on such a large population scale like the brain from the use of wireless phones. A few workers such as RF heater sealer or broadcast technicians may experience high exposure levels as well, however, this concerns only a relatively small population and is not relevant for children. For this reason epidemiologic research on the carcinogenicity of RF-EMF or microwave radiation has mainly used wireless phone use as a proxy for exposure.

Case-Control Studies

So far, results on the association between wireless phone use and childhood brain tumor have been published from one multicenter case-control study conducted in Denmark, Norway, Sweden and Switzerland (CEFALO study) (Aydin et al. 2011c). An additional multicenter case-control study is ongoing in 13 countries (http://www.mbkds.net/), however, no results are available up to now.

In CEFALO, all children and adolescents aged 7–19 years and diagnosed with a brain tumor between 2004 and 2008 in the participating countries were eligible for the study. For each patient, two controls of the same age, gender and region of residence were randomly selected from population registries.

The data were obtained by personal interviews with the study participants and their parents. All participants having used a mobile phone for at least 20 calls were asked about their usage patterns prior to diagnosis. The frequency and duration of mobile phone use was inquired for various time periods as well as the preferred side of the head and the use of hands-free kits. Furthermore, connection data from mobile phone operators were obtained whenever possible.

Data on other possible risk factors for brain tumors such as diagnostic x-ray radiation, infectious diseases and head injuries during childhood were also collected and considered in the analysis.

The association between mobile phone use and brain tumor risk was evaluated by comparing the duration and intensity of mobile phone use between cases and controls in conditional logistic regression analyses. In addition, several sensitivity analyses were conducted. For instance, the brain tumor incidence rates in Swedish children and adolescents between 1990 and 2008 as registered in the nationwide cancer registry were compared with the number of mobile phone users assuming various scenarios for hypothetical increased risks related to mobile phone use.

Overall, 352 patients and 646 controls participated in the study. The participation rates were 83% for cases and 71% for controls. Fifty-five percent of patients and 51% of controls reported regular mobile phone use (at least one call per week during at least 6 months). In the primary analysis, brain tumor risk was not significantly associated with regular mobile phone use (Odds ratio [OR] = 1.36, 95% Confidence interval [CI]: 0.92–2.02). Other exposure metrics, such as time since first mobile phone use or cumulative number and duration of calls, were also not significantly associated with brain tumors and no consistent exposure-response relationship was observed (Fig. 29.2). The risk of tumors in the brain regions most highly exposed by mobile phones (temporal lobe, frontal lobe and cerebellum) was not associated with regular mobile phone use. Regarding preferred side of the head for using the mobile phone, tumors did not occur more often on the ipsilateral compared to the contralateral side. Cordless phone use and use of baby monitors in early childhood was also not related to an increased brain tumor risk. Objective operator data were available for only a third of the study participants who reported to have a mobile phone subscription. In this small, not randomly selected, subset, brain tumor risk was elevated for participants with the longest period since first subscription (>2.8 years) (OR = 2.15 [95%CI: 1.07–4.29]). Calculations demonstrated that such a risk, if true, would have resulted in an increase of brain tumor incidence by approximately 50% in the last few years. Such an increase was not observed in Swedish children and adolescents (Aydin et al. 2011c).

Fig. 29.2

Odds ratio (OR) and 95% confidence intervals from the multicenter CAFALO case-control study on brain tumors associated with times since first subscription (in years), cumulative duration of mobile phone use (in hours) and cumulative number of calls (Aydin et al. 2011c)

Overall, the pattern of the risk results does not suggest a causal association. First, in most analyses there was no consistent exposure-response association observed. Second, the brain tumor risk was not elevated in brain regions that are most exposed when using a mobile phone. Third, the brain tumor incidence in children and adolescents in Sweden, where the most recent data were available, has rather decreased than increased between 2000 and 2008. Thorough sensitivity analyses found no indication that the results were biased due to selective participation of controls or more pronounced overestimation of mobile phone use among patients compared to controls (Aydin et al. 2011a).

The most striking result of CEFALO is a statistically significant association between the duration of mobile phone use and brain tumor risk in the small subset of the study sample with operator data. Objective data are presumed to be more reliable than self-reported data (Aydin et al. 2011b). However, the absent increase of the brain tumor incidence based on high quality registry data strongly contradicts the observed associations. One alternative explanation might be that more patients than controls succeeded in making operator data for more distant time periods available, by having reported changes in subscriptions more completely than controls. Also, cases may have changed subscriptions or phone numbers less often than controls. Thus, mobile phone operator data would cover more distant time periods in cases than controls. This would lead to an erroneous notion that cases started to use mobile phones earlier than controls. Another possibility is the presence of prodromal symptoms before diagnosis in some case patients. To provide frail children with better protection, their parents may have given them a mobile phone subscription for use in case of emergencies.

Ecological Studies

Because mobile phone use among children and adolescents has steeply increased since the mid-1990s, a brain tumor risk after a few years of mobile phone use is to be expected to affect the brain cancer incidence rate in this particular age group. Thus, various researchers have evaluated whether brain tumor incidence time trends have shown increases in the last few years.

Using data collected by the Surveillance, Epidemiology and End Results (SEER) Program for the United States, brain tumor incidence time trends of the age group 0–19 years were separately estimated for 1977–1991 (introduction of computerized tomography, CT, and magnetic resonance imaging, MRI) and for 1992–2006, when mobile phones became more prevalent (Inskip et al. 2010). An analysis of the gender specific incidence trends revealed stable rates for both periods and genders. Another analysis of the SEER data for the 5–19 years old persons revealed also stable incidence time trends between 1990 and 2007 (Boice and Tarone 2011).

A study from the Nordic countries found stable incidence rates of malignant and benign childhood central nervous system neoplasms in children aged 0–10 years between 1985 and 2006, and concluded that major changes in environmental risk factors are unlikely (Schmidt et al. 2011). For the children aged 10–14 years a statistically significant increase in incidence of 1.02% per year was observed for the full period. An analysis of the Nordic country incidence data for the age group 5–19 years did not reveal increasing incidence rates between 1990 and 2008 (Söderqvist et al. 2011).

In England, no time trends in newly diagnosed brain cancer cases in England was observed between 1998 and 2007 among adolescents aged 10–20 years (de Vocht et al. 2011), and the same pattern was observed for malignant brain tumor incidence rates in children and adolescents 0–19 years old in Australia 2000–2008 (Dobes et al. 2011).

In conclusion, incidence rate data from high quality cancer registries with virtually complete registration rates do not indicate an increase of brain cancers among children and adolescents up to 2008.

Discussion and Conclusion

Use of mobile phones among children and adolescents is still a relatively novel phenomenon. So far only little epidemiological research has been conducted to elucidate the role of mobile phone use in the etiology of childhood brain tumors. There is only one case-control study available and a few analyses from pediatric brain tumor incidence rates from the United States, England, Australia, and the Nordic Countries. Altogether these studies do not indicate that use of mobile phone is a major risk factor for childhood brain tumor.

Only gold members can continue reading. Log In or Register to continue