Use of Mobile Phones and Risk of Brain Tumours
Objective To investigate the risk of tumours in the central nervous system among Danish mobile phone subscribers.
Design Nationwide cohort study.
Setting Denmark.
Participants All Danes aged ≥30 and born in Denmark after 1925, subdivided into subscribers and non-subscribers of mobile phones before 1995.
Main outcome measures Risk of tumours of the central nervous system, identified from the complete Danish Cancer Register. Sex specific incidence rate ratios estimated with log linear Poisson regression models adjusted for age, calendar period, education, and disposable income.
Results 358 403 subscription holders accrued 3.8 million person years. In the follow-up period 1990-2007, there were 10 729 cases of tumours of the central nervous system. The risk of such tumours was close to unity for both men and women. When restricted to individuals with the longest mobile phone use—that is, ≥13 years of subscription—the incidence rate ratio was 1.03 (95% confidence interval 0.83 to 1.27) in men and 0.91 (0.41 to 2.04) in women. Among those with subscriptions of ≥10 years, ratios were 1.04 (0.85 to 1.26) in men and 1.04 (0.56 to 1.95) in women for glioma and 0.90 (0.57 to 1.42) in men and 0.93 (0.46 to 1.87) in women for meningioma. There was no indication of dose-response relation either by years since first subscription for a mobile phone or by anatomical location of the tumour—that is, in regions of the brain closest to where the handset is usually held to the head.
Conclusions In this update of a large nationwide cohort study of mobile phone use, there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.
The number of mobile phone users is constantly increasing with more than five billion subscriptions worldwide in 2010. The widespread use of mobile phones has led to concerns regarding potential adverse health effects, particularly tumours of the central nervous system, of which the brain is the part most exposed to the radio frequency electromagnetic fields emitted by an operating mobile phone held to the ear. So far, the mechanism of potential non-thermal interaction between radio frequency electromagnetic fields and living systems is unknown. The results of the Interphone study, the largest international case-control study on this topic, generally suggest no increased risk of glioma or meningioma. For glioma, however, an increased risk (odds ratio 1.40, 95% confidence interval 1.03 to 1.89) was observed in 364 people with more than 1640 hours of cumulative use. Results for long term mobile phone users (≥10 years) remain scarce, and all epidemiological studies are based on few cases. In addition, most studies have been retrospective case-control studies with self reported data on mobile phone use, which are prone to bias, particularly random reporting bias and differential recall bias for cases and controls, which hampers the risk estimation and precludes firm conclusions.
The only cohort study investigating mobile phone use and cancer to date is a Danish nationwide study comparing cancer risk of all 420 095 people who had signed a mobile phone contract with a phone company (subscribers) from 1982 (the year such phones were introduced in Denmark) until 1995, with the corresponding risk in the rest of the adult population with follow-up to 1996 and then 2002. The study found no evidence of any increased risk of brain or nervous system tumours or any cancer among mobile phone subscribers. There was, however, a decreased risk (standardised incidence ratio 0.66, 0.44 to 0.95) of developing a tumour of the brain or nervous system in people who had had a subscription for more than 10 years, but this result was based on only 28 cases. In addition, it was observed that male mobile phone subscribers were at a lower risk (standardised incidence ratio 0.88, 0.86 to 0.91) of developing tobacco related cancers. Additional investigations showed that early male subscribers probably constituted a unique subgroup of people with a higher income and therefore a potentially distinct risk profile, particularly lower tobacco consumption.
We followed up the mobile phone subscriber study to 2007, with a focus on tumours of the central nervous system. Longer follow-up increased the numbers of person years for subscribers, particularly in long term subscribers (≥10 years), in whom the total of person years under risk increased from 170 000 to 1.2 million. This allowed more detailed analysis of long term subscribers and topographical and morphological subtypes of intracranial central nervous system tumours. In addition, we were able to obtain information on socioeconomic status on an individual level, allowing adjustment for education and income when estimating risks related to mobile phone use.
Abstract
Objective To investigate the risk of tumours in the central nervous system among Danish mobile phone subscribers.
Design Nationwide cohort study.
Setting Denmark.
Participants All Danes aged ≥30 and born in Denmark after 1925, subdivided into subscribers and non-subscribers of mobile phones before 1995.
Main outcome measures Risk of tumours of the central nervous system, identified from the complete Danish Cancer Register. Sex specific incidence rate ratios estimated with log linear Poisson regression models adjusted for age, calendar period, education, and disposable income.
Results 358 403 subscription holders accrued 3.8 million person years. In the follow-up period 1990-2007, there were 10 729 cases of tumours of the central nervous system. The risk of such tumours was close to unity for both men and women. When restricted to individuals with the longest mobile phone use—that is, ≥13 years of subscription—the incidence rate ratio was 1.03 (95% confidence interval 0.83 to 1.27) in men and 0.91 (0.41 to 2.04) in women. Among those with subscriptions of ≥10 years, ratios were 1.04 (0.85 to 1.26) in men and 1.04 (0.56 to 1.95) in women for glioma and 0.90 (0.57 to 1.42) in men and 0.93 (0.46 to 1.87) in women for meningioma. There was no indication of dose-response relation either by years since first subscription for a mobile phone or by anatomical location of the tumour—that is, in regions of the brain closest to where the handset is usually held to the head.
Conclusions In this update of a large nationwide cohort study of mobile phone use, there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.
Introduction
The number of mobile phone users is constantly increasing with more than five billion subscriptions worldwide in 2010. The widespread use of mobile phones has led to concerns regarding potential adverse health effects, particularly tumours of the central nervous system, of which the brain is the part most exposed to the radio frequency electromagnetic fields emitted by an operating mobile phone held to the ear. So far, the mechanism of potential non-thermal interaction between radio frequency electromagnetic fields and living systems is unknown. The results of the Interphone study, the largest international case-control study on this topic, generally suggest no increased risk of glioma or meningioma. For glioma, however, an increased risk (odds ratio 1.40, 95% confidence interval 1.03 to 1.89) was observed in 364 people with more than 1640 hours of cumulative use. Results for long term mobile phone users (≥10 years) remain scarce, and all epidemiological studies are based on few cases. In addition, most studies have been retrospective case-control studies with self reported data on mobile phone use, which are prone to bias, particularly random reporting bias and differential recall bias for cases and controls, which hampers the risk estimation and precludes firm conclusions.
The only cohort study investigating mobile phone use and cancer to date is a Danish nationwide study comparing cancer risk of all 420 095 people who had signed a mobile phone contract with a phone company (subscribers) from 1982 (the year such phones were introduced in Denmark) until 1995, with the corresponding risk in the rest of the adult population with follow-up to 1996 and then 2002. The study found no evidence of any increased risk of brain or nervous system tumours or any cancer among mobile phone subscribers. There was, however, a decreased risk (standardised incidence ratio 0.66, 0.44 to 0.95) of developing a tumour of the brain or nervous system in people who had had a subscription for more than 10 years, but this result was based on only 28 cases. In addition, it was observed that male mobile phone subscribers were at a lower risk (standardised incidence ratio 0.88, 0.86 to 0.91) of developing tobacco related cancers. Additional investigations showed that early male subscribers probably constituted a unique subgroup of people with a higher income and therefore a potentially distinct risk profile, particularly lower tobacco consumption.
We followed up the mobile phone subscriber study to 2007, with a focus on tumours of the central nervous system. Longer follow-up increased the numbers of person years for subscribers, particularly in long term subscribers (≥10 years), in whom the total of person years under risk increased from 170 000 to 1.2 million. This allowed more detailed analysis of long term subscribers and topographical and morphological subtypes of intracranial central nervous system tumours. In addition, we were able to obtain information on socioeconomic status on an individual level, allowing adjustment for education and income when estimating risks related to mobile phone use.
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