Publication of a landmark study into cellphones and brain cancer was delayed for years because scientists failed to agree on its findings and whether to issue a warning about excessive use of the devices.
The World Health Organisation’s Interphone report was due to be published in 2006, but was held up until this week because scientists from 13 countries interpreted the results differently.
In the study more than 5 000 men and women with brain tumours, and a similar number of healthy controls, were interviewed about their cellphone use. Scientists then looked at whether those who had been diagnosed with tumours used their phones more.
The interviews found no solid evidence that cellphones increased the risk of brain tumours, but pointed to a slightly greater risk among those who reported using mobile phones the most.
According to the study, the 10% who used their phones the most, racking up at least 1 640 hours of calls, had a 15% greater risk of meningioma and were 40% more likely to develop glioma. These are the two most common brain cancers, although still exceptionally rare, affecting less than seven in 100 000 people in Britain.
The most frequent cellphone users were also more likely to have a tumour on the same side of their brain as the ear they put their phone to, the study found. There were disagreements about the severity of flaws in the study, some of which could have led to an artificial rise in cancer risk among the most frequent users.
People are poor at remembering for how long they have been on the phone, and only slightly better at remembering how many calls they made. Some participants claimed they used mobiles for more than 12 hours a day, a figure that skewed the results but is unlikely to be true.
Another confusing aspect of the study was that it appeared to show that modest use of a cellphone actually reduced the risk of brain cancer. The effect may be false because of volunteers in the control group being healthier than the general population or otherwise unrepresentative.
‘We had to find a version everyone could live with,” said a researcher. Two appendices that were published online, but not with the main Interphone study, claim the risk of tumours may be higher than the report claims.
As yet , scientists know of no mechanism by which mobile phone radiation could cause cancer. Unlike x-rays, cellphone radiation is non-ionising, and is too weak to break apart DNA, which is necessary to induce other cancers.
Scientists concede, however, that there may be unknown effects that trigger cancer, or that cellphone radiation speeds the growth of existing brain tumours.
Patricia McKinney, an epidemiologist at Leeds University who led the northern UK part of the study, said: ‘This research has not shown evidence of an increased risk of developing a glioma or meningioma brain tumour as a result of using a mobile.”
In the report the Interphone study group writes: ‘There were suggestions of an increased risk of glioma, and much less of meningioma, at the highest exposure levels . . . However, biases and errors limit the strength of the conclusion we can draw — and prevent a causal interpretation. ” —