Use of mobile phones and risk of brain tumours: update of Danish cohort study by Patrizia Frei, Aslak H Poulsen, Christoffer Johansen, Jorgen H Olsen, Marianne Steding-Jessen, and Joachim Schuz
This misleading study has many flaws and serious confounders and should not give anyone reassurance that mobile phone use is not associated with an increase in brain tumours. In our opinion the paper should not have been published in this form — it should have failed peer-review. We recommend that it is disregarded as low quality science.
Denis Henshaw, Emeritus Professor of Human Radiation Effects at the University of Bristol agrees with this view: "This seriously flawed study misleads the public and decision makers about the safety of mobile phone use. I consider that their claims are worthless."
What the BMJ Press Release says:
"There is no link between long-term use of mobile phones and tumours of the brain or central nervous system, finds new research published on bmj.com today. In what is described as the largest study on the subject to date, Danish researchers found no evidence that the risk of brain tumours was raised among 358,403 mobile phone subscribers over an 18-year period."
What do we see as the main problems?
The Abstract wrongly claims "The risk of such tumours was close to unity for both men and women." when it means "The relative risk of such tumours..."
This study only looks at 7% of the Danish population who had a personal mobile phone subscription for at least one year during the period 1987 to 1995.
They had few women subscribers in their cohort. In this new analysis they have 6% of the Danish population as male mobile phone users and only 1% as female mobile phone users. By the end of the study period (2007) about 90% of the population were mobile phone users (but were still classified as non-users!).
Pre-1995 almost all these subscribers used analogue mobile phones which operate quite differently to GSM and 3G handsets used since 1995. Analogue mobile phones were slightly higher powered but did not pulse in the way GSM phones do.
It did not analyse corporate subscribers (the heaviest users in the 1987-1995 period). In total it placed these 36% of total users from that period in the "non-users" group of the general population.
The researchers have no data at all on mobile phone use since 1995 so the extra 88% of the population who started to use a mobile phone after 1995 were left in the "non user" part of the population. That will seriously damage and distort any data analysis. Other studies have shown increases in brain tumours in the first 10 years of use - these "non-users" could have actually have used a mobile phone for up to 12 years.
The researchers have assumed that anyone having at least a one-year a mobile phone contract in the period 1987 to 1995 will have continued to have one up to 2007. They even put categories in their tables for up to 13 years of use - yet they have no actual evidence that these people did continue having a mobile phone contract, however likely or unlikely that is.
They did not control for cordless phone use. This is despite the first author (Frei) having published a paper showing that a third of a person's microwave exposure can come from cordless phone use (with another third from mobile phone use and the other third from base stations and other UHF transmitters). Professor Lennart Hardell has repeatedly shown increases in brain tumours associated with extensive cordless phone use - any such cases would occur in the "non-users" group and reduce any effect in the cohort group.
They lost 37,093 people from the user cohort because their either died or emigrated. This represents a loss of almost 10% of the cohort of 358,403 people.
The new paper admits (our emphasis):
"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."
The IARC panel of 30 scientists who judged RF exposure as a Class 2B possible human carcinogen in May 2011, commented on the 2006 paper of the Danish Cohort study: "In this study, reliance on subscription to a mobile phone provider, as a surrogate for mobile phone use, could have resulted in considerable misclassification in exposure assessment." [Lancet, 22 June 2011]
Frei P, et al. Use of mobile phones and risk of brain tumours: update of Danish cohort study.
British Medical Journal. E-pub 21 October 2011. [download the paper]
Ahlbom and Feychting BMJ Editorial.
British Medical Journal. E-pub 21 October 2011. [download the editorial]
Schuz J, et al. Cellular telephone use and cancer risk: update of a nationwide Danish cohort.
J Natl Cancer Inst. 2006 Dec 6;98(23):1707-13. [download the paper]
Kundi, M. Letter regarding the 2006 paper:
Cellular telephone use and cancer risk: update of a nationwide Danish cohort. [download the letter]