The world's largest study into the link between mobile phones and brain tumors is inconclusive according to a Canadian scientist. Over 10,000 people took part in the study led by epidemiologists from more than ten countries but the findings, according to University of Montreal professor Jack Siemiatycki, are "ambiguous, surprising and puzzling."

Siemiatyck, who is also an epidemiologist at the University of Montreal Hospital Research Center, collaborated on the Interphone International Study Group along with epidemiologists from Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden and the United Kingdom.

Coordinated by the International Agency for Research on Cancer, the study looked cellular radio frequencies could be correlated to brain tumors. Participants included cell phone users, non cell phone users, cell phone users who survived brain cancer as well as brain cancer survivors who had never used cell phones.

While the findings do indicate an increased risk for heavy phone users, they are compromised by the restricted access to participants according to Siemiatyck.

"If we combine all users and compare them with non-users, the Interphone Study found no increase in brain cancer among users. In fact, surprisingly, we found that when we combine users independently of the amount of use, they had lower brain cancer risks than non-users," he says. "However, the study also found heavy users of cell phones appeared to be at a higher risk of brain tumors than non-users."

The paradoxical results are possibly a result of the methodology, with concerns that participants did not provide an accurate portrait of cell phone usage among cancer cases and among healthy control subjects.

"Ethics reviews are now so rigid that scientists from Canada, the United States and Europe are losing the kind of access to medical databases and to study subjects that is needed to conduct studies such as this one," says Siemiatyck. "Ethics committees increasingly require that researchers work through treating physicians, professionals who are already overworked, to recruit their patients. This may work for clinical research exploring treatment of cancer, in which physicians often have a professional or personal interest, but it does not work for investigations into the causes of cancer. This flawed system can produce biased study results.

"If there are risks, they are probably pretty small. Should anyone be concerned about potential dangers of cell phones, they can remedy the issue by using hands-free devices and avoid exposure to radio frequencies around their head."

The study is published this month in the International Journal of Epidemiology.