Mobile phones increase metabolic activity in some parts of the brain during a long telephone call, new research shows. Yet the 47-person study, published today in JAMA, offers no evidence for – or against – the controversial claim that mobile phones may cause brain cancer, its authors and other scientists emphasize.
Studies of brain cancer rates among large numbers of people have been difficult to interpret: Some have found slightly higher rates of brain cancers among cell phone users, others lower rates and many documented no change at all.
Even the studies showing an increased risk of brain cancer for cell phone users can’t say anything about whether mobile phone use causes cancer. But if cell phones could influence brain cancer, there must be a plausible scientific explanation as to how. The new JAMA study represents a toe dipped into the Olympic-size swimming pool that is determining such a mechanism.
Nora Volkow, a neuroscientist who directs the National Institute of Drug Abuse, and her colleagues placed cell phones receiving 50-minute muted calls near the right ears of 47 men and women. Then the participants underwent a positron emission tomography (PET) brain scan, which measured brain metabolism via the levels of radioactive glucose molecules injected into their bloodstream. On a different day, the volunteers went through the same routine, except with the phones switched off, emitting no electromagnetic radiation.
The brain regions nearest the antenna, including the right orbital frontal cortex and temporal pole, consumed more glucose when the cell phone was switched on, compared to off, Vokow’s team found. However the increase in metabolism, about 7%, was modest. For comparison, the metabolism of the visual cortex may spike by as much as 50% when people look at a pattern on a computer screen.
Volkow’s team conclude that the human brain is sensitive to the radiation from a mobile phone call. But they emphasize that their findings say nothing about whether or how such radiation could promote brain cancer. Moreover, it is not clear how cell phone radiation influences brain activity, nor how such activity could promote tumours.
“If this is real, then the question about the possible mechanism arises,” says Michael Kundi, at the Medical University of Vienna, Austria. “At present I can only think of an influence on tumor growth. Since a brain tumor utilizes excessive amounts of glucose, changes in glucose utilization may be a key mechanism to support tumor growth.”
In an editorial accompanying the paper, Henry Lai of the University of Washington in Seattle and Lennart Hardell at University Hospital in Orero, Sweden, say the results add to concerns over the health effects of emissions from wireless and cordless phones and deserve follow-up.
However other scientists are more critical. “We are really surprised by the significant result given by the authors,” says Yasuo Terao of the University of Tokyo. “We have also done some studies addressing the effect of electromagnetic radiation on physiological measures and behaviours and always found negative results.”
Patrick Haggard, a neuroscientist at University College London, said in a statement sent to reporters, that “the result should be treated with some caution.” The experiment hasn’t been replicated by another group, and it is also possible that participants knew when the phone was on, even when muted, potentially affecting their brain activity.
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