Experts who studied almost 13,000 cell phone users over 10 years, hoping to find out whether the mobile devices cause brain tumours, said on Sunday their research gave no clear answer. A study by the World Health Organisation's International Agency for Research on Cancer (IARC), the largest ever to look at possible links between mobile phones and brain cancer, threw up inconclusive results but researchers said suggestions of a possible link demanded deeper examination. “The results really don't allow us to conclude that there is any risk associated with mobile phone use, but… it is also premature to say that there is no risk associated with it,” the IARC's director Christopher Wild told Reuters. The results of the study have been keenly awaited by mobile phone companies and by campaign groups who have raised concerns about whether mobile phones cause brain tumours.

Years of research have failed to establish a connection. Wild said part of the problem with this study, which was launched in 2000, was that rates of mobile phone usage in the period it covered were relatively low compared with today. It was also based on people searching their memories to estimate how much time they spent on their cell phones, a method that can throw up inaccuracies. European scientists last month launched what will now become the biggest ever study into the effects of mobile phone use on long-term health. It aims to track at least a quarter of a million of people in five European countries for up to 30 years.

This kind of study, called a prospective study, is considered more accurate because it does not require people to remember their cell phone use later but tracks it in real time. SUGGESTION OF A RISK? Data from the IARC study showed that overall, mobile telephone users in fact had a lower risk of brain cancer than people who had never used one, but the 21 scientists who conducted the study said this finding suggested problems with the method, or inaccurate information from those who took part. Other results showed high cumulative call time may slightly raise the risk, but again the finding was not reliable.