The use of mobile phones and the risk of brain tumors among children and adolescents

Mobile phones experienced a steep rise in popularity among children and adolescents during the last decade. The increase in popularity has been reflected in both increased ownership and increased usage of mobile phones. Most children start to use mobile phones when they are around 9–10 years old, but usage before school age is not uncommon. The increase in mobile phone use has raised concerns about possible adverse health effects. Brain tumors have been a main concern because the brain absorbs most of the radio frequency energy emitted by mobile phones during calls. In addition, it has been hypothesized that children may be more vulnerable to radio frequency electromagnetic fields (RF-EMFs) because their nervous system is developing, their brain tissue is more conductive than that of adults, and RF-EMFs penetrate in to regions that are deeper in their brains. Radio frequency radiation emitted by mobile phones has insufficient energy to directly damage the DNA and the only known effect of RF-EMFs is heating of the tissue. Studies about mobile phone use and brain tumor risk among adults have shown no increased risk for regular users but have been inconclusive regarding long-term (≥10 years) and heavy mobile phone use. The largest case-control study so far, INTERPHONE, found an increased risk for glioma among heavy users (≥1640 lifetime calls). Another study from a Swedish research group reported a five-fold increased risk for astrocytoma for adults who first used mobile phones before the age of 20. No study has addressed the association between mobile phone use and brain tumor risk among children and adolescents so far. The goal of this thesis was to assess whether there is a relationship between mobile phone use and brain tumor risk among children and adolescents or not. In 2006, we set up CEFALO, an international case-control study about the relationship between mobile phone use and brain tumor risk in children and adolescents aged 7–19 years. CEFALO was performed in Denmark, Sweden, Norway, and Switzerland. The study period ranged from 2004 through 2008. Children and adolescents of age 7–19 years who were diagnosed during the study period with a primary brain tumor were eligible. For each case patient, we selected two healthy controls matched by age, sex and geographical region of residence using population registries. Exposure data was collected by face to face interviews with the study participants accompanied by at least one parent. Risk estimates for brain tumors were calculated for various exposure surrogates. We also examined the gender and age-adjusted brain tumor incidence rates among Swedish children and adolescents aged 5–19 years from 1990 to 2008 including hypothetical incidence rate trends based on the risk estimates found in our analyses. Lastly, we compared the self-reported amount of mobile phone use with objectively recorded data by network operators. Regular users of mobile phones were not statistically significantly more likely to have been diagnosed with brain tumors compared with non-regular users (OR=1.36, 95%-CI: 0.92 to 2.02). No clear exposure-response relationship was observed for any exposure surrogate. Moreover, no exposure-response relationship was seen in terms of localization of the tumor. For the study participants for whom operator-recorded data were available, we found a statistically significantly increased risk among users with more than 2.8 years since the start of the first subscription (OR=2.15). The odds ratio for brain tumor risk among ipsilateral regular users of mobile phones was not higher than the odds ratio of contralateral regular users. The risk estimate of 2.15 after 3 years of regular mobile phone use is incompatible with the stable (or even downward) incidence trends observed among Swedish children and adolescents aged 5–19 years from 1990 to 2008. This indicates that short-term use of mobile phones does not cause brain tumors in children and adolescents. In the validation study, cases overestimated their cumulative number of calls by 9% on average and controls by 34%. Cases also overestimated their cumulative duration of calls by 52% on average and controls by 163%. We found little evidence for differential recall errors. CEFALO is the first study to investigate the relationship between mobile phone use and brain tumor risk in children and adolescents. We found no consistent evidence for a causal association between short-term mobile phone use and brain tumor risk among children and adolescents. The lack of an exposure-response relationship either in terms of the amount of mobile phone use or by localization of the brain tumor argues against a causal relationship. These findings are corroborated by the fact that brain tumor incidence rates among children and adolescents have not increased in many countries in recent times. We cannot, however, exclude the possibility of a small increase in brain tumor risk due to mobile phone use. As we found that self-reported mobile phone use is affected with large random and some systematic recall errors, we emphasize the importance of future studies with objective exposure assessment or the use of prospectively collected exposure data. We also recommend the monitoring of time trends in brain tumor incidence rates as increased risks should be reflected in future brain tumor incidence rate trends.