Talking on the mobile phone for more than half an hour a day could increase your risk of getting brain cancer by as much as 40 per cent, a landmark study suggests.
The biggest investigation of its kind to date found that people who talk daily on a cell phone have an increased risk of developing a tumour.
Despite scientists in 13 countries contributing to the 10 year, £15 million Interphone project, they admitted that the findings are not definitive and are open to statistical error or bias.
"We can't just conclude that there is no effect," said Elisabeth Cardis of the Centre for Research in Environmental Epidemiology in Barcelona, Spain, who led the study.
"There are indications of a possible increase. We're not sure that it is correct. It could be due to bias, but the indications are sufficiently strong ... to be concerned."
The study was started by the International Agency for Research on Cancer (IARC), an agency of the UN’s World Health Organisation, in 1998 to investigate whether exposure to mobile phones is linked to the development of three types of brain tumour.
It was known that radiofrequency radiation emitted by mobiles is absorbed by the body, much of it by the head when the handset is held to the ear.
But research into whether frequent mobile phone use damages health had proved inconclusive, mainly because of the short time since the technology became widely used.
Between 2000 and 2004, researchers therefore interviewed tumour sufferers and those in good health – 12,800 in total – to see if their mobile phone use differed.
But for heavy users – those that used the phone for more than 1640 hours over the last 10 years – an average of just over half an hour a day – did show an increase of 40 per cent for glioma – the most common type of brain tumour – and 15 per cent for less common kinds.
The British team believes that the study suffered because it involved asking tumour patients to recall their use over the last 10 years and that many memories may be flawed – especially if the brain is damaged.
The research was published in the International Journal of Epidemiology.