Mobile phones and cancer
Many
of us use mobile telephones to a greater or lesser extent. Because mobile
phones emit radio frequencies that can penetrate several centimetres into the
human brain, it has been hypothesised that their use could possibly lead to
tumours of the head and neck.
This
possibility has led to a number of 'scare' stories in the popular
press. Typically, debunking the scare involves trying to prove a negative,
never an easy thing at the best of times. About the only way to prove a
negative is to have very large amounts of data, but also demonstrating the lack
of any sort of dose-response as well as no biological plausibility. A large
Danish study goes most of the way to doing that for mobile phones and cancer [1].
Study
In
the period 1982 to 1995 over 700,000 Danish citizens subscribed to a mobile
telephone service. After eliminating those in which individual users could not
be identified because they were corporate subscriptions, had incorrect
addresses, were from Greenland or the Faroe islands, had a history of previous
cancer, or were under 18 years, the final cohort consisted of 420,000
identified subscribers.
Because
Denmark has a system of personal identification numbers, cohort members could
be linked to files of a cancer registry that is virtually complete, and using a
nationwide system of cancer classification. Follow up began from the first day
of subscription, and ended on date of diagnosis of any cancer, death,
emigration, or end 2002.
Numbers
of cancers found were compared with the number expected in the general Danish
population, for men and women, and in five-year age groups. Mobile phone
subscribers were omitted from this comparison group.
Results
Most
(85%) of the 420,000 subscribers were men. The median time of mobile telephone
subscription was 8.0 years. Mobile subscribers had 14,250 cases of diagnosed
cancer, against an expected number of 15,000, giving an overall standardised
incidence ratio of 0.95 (95% confidence interval of 0.93 to 0.97).
For
men and women analysed separately there was no difference from expected in all
brain and nervous system cancers, or cancers of the salivary glands or eye. For
men and women analysed together, there was no increased risk of any type of
intracranial cancer, with a hint of a decreased risk for parietal lobe tumours.
There was no increase in brain and nervous system tumours and leukaemias
according to time from first subscription (Table 1).
Table 1: Brain and nervous system cancers, and leukaemias, by years of mobile phone subscription, compared with non-subscribers in Denmark
(95%CI) |
|||
| Years of subscription | |||
| <1 | |||
| 1-4 | |||
| 5-9 | |||
| ≥10 | |||
There
was no increased risk of any other type of cancer for men, with hints of
decreased risk for lung, bladder, buccal, oesophageal and liver cancers, as
well as other cancers and unspecified cancers. For women the numbers of
individual cancers were small, and none had any large increase or decrease in
incidence over expected.
Comment
What
is good about this study is that it was large, of long duration, covered a
whole population, and was performed in Denmark. Denmark has an almost unique
ability to successfully link different databases through the use of personal
identification numbers.
The
results all but eliminates the concept that the use of mobile phones can cause
cancer. And not just cancer, because the study allows detailed diagnosis of
particular cancer types, including acoustic neuromas and cancers of temporal
and parietal lobes which would be the parts of the brain closest to a mobile
phone antenna, and hence most at risk.
The
paper has a wonderful discussion, which not only puts these results into the
context of others, but tells us that the authors could find no studies
indicating any biological plausibility for a link between mobile phones and
cancer. This comes a close to proving a negative as we are ever likely to get,
but even more data will come out in future from continuation and extension of
the study.
If
you Google mobile phones and cancer, you will find links to over nine million
sites. Some are good, some are up to date, but many are not. They should all
reflect on the data from Denmark.
Reference:
- J Schüz et al. Cellular telephone use and cancer risk: update of a nationwide Danish cohort. Journal of the National Cancer Institute 2006 98: 1707-1713.