20 October 2011 – London – A new study published today in the British Medical Journal concludes that mobile phone use does not raise the risk of getting a brain tumour. But scientists and campaigners both in the UK and internationally have dismissed the study as seriously flawed and as offering false reassurance to the media and public.
The study, Use of mobile phones and risk of brain tumours: update of Danish cohort study, looked at data on the Danish population aged 30-plus. Dividing this into subscribers and non-subscribers of mobiles before 1995, they compared the brain tumour rates between the two groups. The apparent conclusion was that there was no increase in brain tumours among mobile phone subscribers.
However, the finding is seriously misleading, according to scientists and campaigners in the UK and the US who have examined the data.
First, it implies that it was studying long-term users (which is crucial when looking at brain tumours, as they take about 30 years to develop), when in fact the phones had only been used for between one and seven years.
Secondly, the study excluded business users, who were by far the heaviest in Denmark in the 1990s. This removed those at highest risk of tumours, severely inflating the apparent risk of the non-mobile users with whom they were compared. It also included as ‘non-users’ people who started using mobiles after the study began.
Together, these methods greatly diminished the difference in risk between mobile users and non-users, resulting in the finding that mobile users ran no significantly higher risk of tumours.
Such are the flaws in the study that Denis Henshaw, Emeritus Professor of Human Radiation Effects at the University of Bristol, considers “the claims in the study to be worthless”. He says that the researchers “misclassified the 88 per cent of the Danish population who started using a mobile phone after 1995. This seriously flawed study misleads the public and decision makers about the safety of mobile phone use.”
Even the researchers have admitted the analysis is flawed. They state: “A limitation of the study is potential misclassification of exposure. Subscription holders who are not using their phone will erroneously be classified as exposed and people without a subscription but still using a mobile phone will erroneously be classified as unexposed. Because we excluded corporate subscriptions, mobile phone users who do not have a subscription in their own name will have been misclassified as unexposed. Also, as data on mobile phone subscriptions were available only until 1995, individuals with a subscription in 1996 or later were classified as non-users.”
Epidemiologist Dr Devra Davis of the Environmental Health Trust in the US emphasised that the study is not new, but an extension of a study already published by the Danish team two years ago that was widely criticised at the time. It was not considered by the World Health Organization to be reliable enough for inclusion in the review that the WHO carried out prior to its classification of mobile radiation as a ‘possible carcinogen’ in May 2011.
Vicky Fobel, director of MobileWise, a charity advising on mobile phones and health, says: “This study and the press release promoting its findings are misleading the public by implying that mobile use has the all-clear. The study only looked at short-term use and by mis-analysing the data has massively underestimated the risks.
“All the other studies that have looked at the long-term risks have found a link between mobile use and brain tumours. This study gives false reassurance and distracts us from the important job of helping the public, especially children, to cut their health risks from mobiles.”
MobileWise is shortly to publish a report highlighting the growing body of evidence that points to a link between mobile phone use and a range of health hazards – including brain tumours, infertility and DNA damage – and the implications of this for public health policy. The report, endorsed by scientists working in the radiation field, is due to be released in early November.
Notes to editors
1. Use of mobile phones and risk of brain tumours: update of Danish cohort study can be downloaded at http://press.psprings.co.uk/bmj/october/mobilephones.pdf <http://press.psprings.co.uk/bmj/october/mobilephones.pdf>
2. MobileWise was set up in 2010 to help children use phones more safely. It has formulated the Safe Mobile Code to offer practical solutions for those who want to cut exposure to phone radiation – particularly to the head and groin, which are shown by research to be vulnerable. For more information on MobileWise and the Safe Mobile Code, go to www.mobilewise.org