The largest and most detailed study yet into the health risks posed by mobile phones has failed to find a link between cellphones and brain cancer, although scientists said that they still cannot give categorical assurances that there are no risks attached to using the devices over long periods of time.
More than 10,000 people from 13 countries took part in the study, which compared mobile phone use among people with brain tumours with healthy "controls". It was the biggest such study by far, yet the researchers found no increase in the risk of getting either of two types of brain tumour – and even detected a slightly lower cancer risk among mobile phone users.
The leaders of the Interphone study, which was co-ordinated by the International Agency for Research on Cancer, said yesterday that there were severe limitations on what the research can say about the cancer risk. As a a result, they refused to give mobile phones a clear bill of health, despite being unable to produce any evidence suggesting that the devices can cause brain tumours.
"It is impossible to say there is no risk whatsoever [but] the study has not shown a raised risk of brain tumours and it has certainly not shown that mobile phones cause brain tumours," said Professor Anthony Swerdlow of the Institute of Cancer Research in Britain, one of the study's main authors.
"The balance of evidence from this study, and in the previously existing scientific literature, does not suggest a causal link between mobile phone use and risk of brain tumours. The duration of phone use for which we have evidence is currently limited, however, and we have virtually no information for use of mobile phones for longer than 15 years," Professor Swerdlow said.
The study, which collated data from a number of smaller studies in each of the 13 countries, compared the mobile-phone usage among about 5,000 brain-cancer patients aged between 30 and 59 who were suffering from either glioma or meningioma [tumours], with mobile-phone usage among a similar number of healthy adults who acted as the controls. No children took part in the study.
This type of "case-control" study relied on interviews with the participants to assess how often they used their mobile phones over a period of up to 10 years previously, which could have introduced some memory bias into the findings. For instance, some of the cancer patients reported that they had used their mobile phones for more than 12 hours a day every day of the year, a heavy usage not reported by the healthy controls.
The scientists thought that this high level of phone use was unlikely and suggested that the memories of some of the patients may have been affected by their medical condition. This is just one of the inherent problems of case-control studies, which have nevertheless proved invaluable in establishing the causes of other types of cancer, such as lung cancer and smoking, the researchers said.
When the scientists looked at the cumulative use of mobile phones they failed to find any incremental increase in cancer risk, which would normally be found if there had been a cause-and-effect relation. However, they did find a statistically significant increased risk of glioma in just the top 10 per cent of heavy users – a finding they put down to the possibility of reporting bias.
"Overall, 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 phone," said Professor Patricia McKinney of Leeds University, another lead author of the study, published in the International Journal of Epidemiology. "This is consistent with published biological studies, which have not established any effect of exposure to radiation from mobile phones at a cellular level, nor found a mechanism by which cancer could be caused," Professor McKinney said.
The radio waves produced by mobile phones are non-ionising, unlike ionising X-rays which are known to cause cancer. They are also not strong enough to damage DNA molecules, in contrast to UV light which is also known to induce cancer. This is why there is no known mechanism according to which mobile phone radiation can cause brain tumours.
Most studies investigating the the health risks of mobile phones have failed to establish a link between the use of the devices and brain tumours. However, a smaller study in Sweden five years ago did find a statistically significant association, but Professor Swerdlow dismissed this as one "outlier" study that bucked the trend.
"The results of our study do not get close to establishing causality. It has not shown a raised risk of brain tumours and it has certainly not shown that mobile phones cause brain tumours," he said.