Increased use of mobile phones since the late 1990s is not causing a rise in the frequency of brain tumours, a Scandinavian study has found.
The survey of cancers reported among 16 million adults in Denmark, Finland, Norway and Sweden found no related, observable change in the incidence of cases up until 2003.
Published in the Journal of the National Cancer Institute, the research covers a more recent period than previous studies. It suggests that if there is any risk from regular use of mobile phones, it would take more than five to 10 years for the tumours to appear.
"The [cause] of brain tumours is poorly understood," the paper, written by Isabelle Deltour of the Danish Cancer Society and others, says. "The only well-established risk factors – ionizing radiation and rare hereditary syndromes – account for a small proportion of brain tumour cases."
The study was based on 59,984 brain tumour cases diagnosed between 1974 and 2003 among 16 million adults aged 20–79 years.
But Deltour said she had found no evidence that using mobile phones increased the risk of brain tumours.
She said: "Radio frequency electromagnetic fields emitted from mobile phones have been proposed as a risk factor for brain tumours; however, a biological mechanism that could explain the potential effect of radio frequency electromagnetic fields in the risk of brain tumours has not been identified.
"During the study period, there was a gradual increase in tumours, but these were almost all observed in the older segment of the population, among the 60- to 79-year-olds.
"From 1974 to 2003, brain tumour incidence rates in Denmark, Finland, Norway, and Sweden were stable, decreased, or continued a gradual increase that started before the introduction of mobile phones. No change in incidence trends was observed from 1998 to 2003, the time when possible associations between mobile phone use and cancer risk would be informative about an induction period of five to 10 years."
The survey's conclusions are consistent with findings of a number of recent papers by other Nordic and British investigations. It contradicts a 2006 study by Swedish scientists that suggested there was "substantially increased risks" for both short- and long-term users of mobiles.
The Interphone inquiry, overseen by the World Health Organisation, has, however, suggested that there may be a slightly heightened long-term risk for heavy users of mobiles.
Calling for further follow-up studies to check that there is no danger, the researchers caution that "open questions about prolonged exposures remain".
The paper concludes that: "The lack of a detectable trend change in incidence rates up to 2003 suggests that [either] the induction period for brain tumours associated with mobile phone use exceeds five to 10 years, the increased risk of brain tumours associated with mobile phone use in this population is too small to be observed, the risk is restricted to subgroups of brain tumors or mobile phone users, or that there is no increased risk associated with mobile phone use."
The UK's Mobile Operators Association (MOA) welcomed the findings in the new study.
Mike Dolan, executive director of MOA, said: "The research reported no increase in incidence rates of brain tumours during a period when mobile phone use increased in Nordic countries.
"This finding is consistent with previous studies in this field and will form part of the overall body of scientific research. The UK mobile phone operators are supporting a large cohort study which is a recommendation of this paper."
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