Scientific statement of the Federal Office for Radiation Protection concerning the results and conclusions of the INTERPHONE international case-control study on the risk of brain tumour in relation to mobile telephone usage

The rapid increase in mobile telephone use has led to general concerns about possible detrimental health risks that may be related to the radio-frequency (RF) electromagnetic fields generated by this technology. The INTERPHONE international case-control study on the risk of brain tumour incidence in relation to mobile telephone usage was initiated in 2000 by the International Agency for Research on Cancer (IARC). It involved extensive epidemiological data and detailed information on mobile phone usage from 13 countries (Australia, Canada,Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway,Sweden and the UK).

The aim of the INTERPHONE study was to assess possible risks for the development of brain tumours, diagnosed during study periods of two to four years between 2000 and 2004, which could be associated with the use of mobile phones. Three types of primary brain tumours were investigated:

• glioma, which is the most common and most aggressive type and arises from the glial cells;
• meningioma, which is the second most common type and arises from the meninges;
• acoustic neuroma, which is a tumour of the acoustic nerve.

Details of the German contribution to the INTERPHONE study, done within the framework of the German Mobile Telecommunication Research Programme (DMF), can be found on the webpages of the DMF.

Methods

The study design was a population based, personal interview based, case-control study with data on 2,708 glioma cases, and 2,409 meningioma cases, 1,105 acoustic neuroma cases and matched controls, conducted in 14 study centres in 13 countries (one study centre per country except in the UK which had two study centres one for north UK and one for south UK). A common protocol was applied in all study centres which involved one control per brain tumour case, except in Germany where two controls per case were drawn. Two controls were selected for acoustic neuroma cases in all countries. The controls were selected from a locally appropriate population-based sampling frame.

Statistical methods applied involved conditional logistic regression for matched sets with reference dates corresponding to case diagnosis. The reference category for the odds ratios (OR) in the main analyses was the set of subjects who reported that they had never been regular mobile phone users. The OR indicates how the detrimental health risk to exposed persons changes relative to the risk to unexposed persons. Unexposed persons were defined as those who reported that they did not use a mobile phone regularly. An OR > 1 indicates an increased risk and an OR <1 indicates a decreased risk.

Exposure covariables included ever having been a regular user (that is, had an average of at least one call per week for a period of at least 6 months), time in years since first regular use, deciles of cumulative number of calls and deciles of cumulative duration of calls.

Different types of analyses were conducted to account for tumour location (because absorption of RF energy from mobile phones is highly localized), and also based on tumour localization with respect to preferred head-side for telephone usage (that is, whether the phone was used predominantly on the same side as the tumour or mainly on the side of the head opposite to the tumour).

Extensive and thorough supplementary analyses complemented the primary analyse to see if any of some 13 different study characteristics (for example study centre, method of calculating accumulated call time, use of matching and conditional analysis) may have introduced biases into the results.

Results

A reduced OR related to ever having been a regular mobile phone user was seen for glioma [OR 0.81; 95 per cent confidence interval (95 %-CI) 0.70–0.94] and meningioma (OR 0.79; 95 %- CI = 0.68–0.91). The analysis of acoustic neuromas was divided in two subgroups that showed the same tendency:

• regular users up to one year (OR=0.85; 95 %-CI = 0.69–1.04) and
• regular users up to five years before reference date (OR 0.95; 95 %-CI = 0.77–1.17).

These results possibly reflect participation bias or other methodological limitations.

No elevated OR was observed 10 years after first phone use for gliomas as well as meningiomas and acoustic neuromas (glioma: OR 0.98; 95 %-CI = 0.76–1.26; meningioma: OR 0.83; 95 %-CI = 0.61–1.14; acoustic neuroma: OR 0.76; 95 %-CI = 0.52–1.11 for regular users up to one year; OR 0.83; 95 %-CI = 0.58–1.19 for regular users up to five years). ORs were < 1.0 for all deciles of lifetime number of phone calls and the first nine deciles of cumulative call time. In the tenth decile of recalled cumulative call time, corresponding to at least 1,640 hours, the OR was 1.40 (95 %-CI = 1.03–1.89) for glioma, and 1.15 (95 %-CI = 0.81–1.62) for meningioma, and 2.79 (95 %-CI = 1.51–5.16) for acoustic neuroma in regular phone users up to five years.

However, implausible values for reported phone use occurred in this group. When 60 subjects who reported more than five hours call time per day were excluded altogether, on the premise that such responses were unreliable, the OR for all diseases decreased and were no longer statistically significant.

When the cumulative call time was put into sub-groups by recency of starting regular use no elevated ORs were observed for long-term users (start of phone use ≥ ten years before reference date) and for medium term users (start of phone use five to nine years before reference date) for all cumulative call time subgroups analysed, respectively. In the short-term user group (start of phone use one to four years before reference date), however, the OR was 3.77 (95 %-CI = 1.25 – 11.4) for gliomas, 4.8 (95 %- CI = 1.49 – 15.4) for meningiomas and 2.79 (95 %-CI = 1.51–5.16) for acoustic neuroma in the group with a recalled cumulative call time of at least 1,640 hours and no elevated ORs were found with a lower call time, respectively.

ORs for glioma tended to be greater in the temporal lobe than in other lobes of the brain, but the CIs around the lobe-specific estimates were wide. ORs for glioma tended to be greater in subjects who reported usual mobile phone use on the same side of the head as their tumour than on the opposite side.

Results of extensive sensitivity analyses produced OR estimates that were well within the 95%-CI of the OR from the main analysis (except in two ORs for meningioma relating to the presentation of the study, that is, whether or not mobile phones were mentioned or not during the data collection personal interview).

Conclusions

This is the largest study of the risk of brain tumours in relation to mobile phone use conducted to date and it included substantial numbers of subjects who had used mobile phones for at least ten years. Overall, no increase in risk of glioma or meningioma was observed with use of mobile phones. There were suggestions of an increased risk of glioma at the highest exposure levels, but biases and error prevent a causal interpretation.

The subjects of the INTERPHONE-study were adults, therefore nothing could be said about the risk of mobile phone use amongst children and teenagers. The majority of mobile phone users in the study were not heavy users by today’s standards. Mobile phone usage has become much more prevalent. Today it is not unusual for teenagers and young adults to use a mobile phone for an hour a day or even more. The possible effects of long-term heavy use of mobile phones require further investigation, especially for those subjects who started frequent use with young ages.

References

INTERPHONE Study Group. Brain tumour risk in relation to mobile telephone use: results of the INTERPHONE international case-control study. Int J Epidemiol 2010 Jun; 39(3):675-94.

INTERPHONE Study Group. Acoustic neuroma risk in relation to mobile telephone use: results of the INTERPHONE international case-control study. Cancer Epidemiol 2011 Oct; 35(5):453-64.