Critics of the study, including a wireless industry lobby group, immediately questioned the results and noted that the same group has previously warned about the cancer risks of coffee and pickles.
The study was carried out by the International Agency for Research on Cancer (IARC), a unit of WHO.
"The conclusion means that there could be some risk, and that we need to keep a close watch for a link between cell phones and cancer risk," said Dr. Jonathan Samet, a USC professor who chaired an IARC working group that for the past week aggregated data from numerous, previous studies to reach its findings.
Heavy cell phone users, defined as those who use the devices for 30 minutes per day or more over ten years, may be particularly at risk for a type of malignant brain cancer known as a glioma, WHO said. In gathering their evidence, the researchers keyed on a previously published study that found a 40% increase in the risk for gliomas in heavy cell phone users.
Based on its findings, the agency formally classified the type of electromagnetic radiation emitted by cell phones as "possibly carcinogenic to humans," but cautioned that more research is needed to establish, or rule out, a definite link. The move is sure to further fuel a controversial debate that has pitted cell phone makers and service providers against health and safety advocates.
CTIA, a lobby group for the wireless industry, suggested that IARC was being overly alarmist and dependent on old data. "IARC conducts numerous reviews and in the past has given the same score to, for example, pickled vegetables and coffee," CTIA said in a statement.
“The IARC working group did not conduct any new research, but rather reviewed published studies. Based on previous assessments of the scientific evidence, the Federal Communications Commission has concluded that ‘[t]here’s no scientific evidence that proves that wireless phone usage can lead to cancer.’ The Food and Drug Administration has also stated that ‘[t]he weight of scientific evidence has not linked cellphones with any health problems,’” CTIA said.
IARC said the topic needs more study and advised that, until more conclusive data is available, cell phone users should minimize risks by using headsets that don't require their phone be near their head, and by texting instead of calling when practical.