Jack Semitic of the University of Montreal said the study was led by 21 epidemiologists from Australia, Britain, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway and Sweden.
The study, published in the International Journal of Epidemiology, involved more than 10,000 study participants, of which 5,150 had brain tumors -- including cellphone users, non-cell phone users, cellphone users who survived brain cancer as well as brain cancer survivors who had never used cellphones.
"If we combine all users and compare them with non-users, the study found no increase in brain cancer among users. Surprisingly, we found that when we combine users independently of the amount of use, they had lower brain cancer risks than non-users," Semitic said in a statement. "However, the study also found heavy users of cellphones appeared to be at a higher risk of brain tumors than non-users."
The team of scientists said they were unsure what accounted for the discrepancy, but Siemiatycki blamed it on rigorous ethics reviews that restrict access to medical databases for research. Instead, researchers must work with treating physicians to recruit study participants.
"This may work for researcher 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."
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