Incidence of brain tumours in rural zones of Sweden was found to be far higher among users of the Global System for Mobile Communication (GSM) network than among rural non-users and also among GSM users in urban areas, the study says.
Its authors say the link is troubling, although they acknowledge that the amount of data is low and wider research is needed to amplify the findings. As for the possible cause, the study suggests that mobile handsets in rural areas deliver a higher dose of electromagnetic radiation because they have to transmit a stronger signal to distant transmission masts.
Transmission masts in urban areas are closer together, which means the phone’s signal and thus radiation level are correspondingly weaker, it says.
The study, headed by Lennart Hardell, a professor of oncology at University Hospital in Örebro, is published on Tuesday in a specialist British journal, Occupational and Environmental Medicine.
The team trawled through a databank of the population of central Sweden, a swathe of the country that includes its major cities as well as the remote countryside.
Around 1,400 adults aged between 20 and 80 were diagnosed with a malignant or benign brain tumour between January 1997 and June 2000.
Their profiles were compared with a similar number of healthy adults, matched for age and sex and living in the same geographical area. The investigators sent out a questionnaire to all, to ask about daily use of mobile and cordless phones.
The study found that how long users spent on the phone had no impact on the probability of being diagnosed with a brain tumour. But where they lived was a big factor, and especially for digital mobile phones.
Residents of rural areas who had been using a digital mobile for more than three years were more than three times likelier to develop a tumour than urban counterparts.
Among those who had been using the phone for more than five years, the risk quadrupled. No such effect was seen for old-fashioned analogue phones or for cordless phones.
The digital GSM system was launched in Sweden 1990, phasing out an analogue phone system that was started in Sweden in 1981. GSM is now the dominant world standard for cellphones.
It uses a signal-intensifying system, called the adaptive power control, to compensate for distances between the user and the transmission mast. The signal intensity depends on the phone type, the model says. Over the past six years, a series of studies, several of them carried out by the Örebro team, have suggested a higher statistical risk of brain tumours among heavy and long-term users of mobile phones.
But the picture is unclear, because other research sees no such link. Watchdog scientists in Britain, France and Sweden and elsewhere have insisted there is no evidence to support claims that mobile phones or their base stations are dangerous to health.
As a precautionary principle, however, children under eight in Britain are being advised not to have their own handsets.
Photo on previous page: Mark Earthy/Pressens Bild/www.imagebank.sweden.se