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And as NPR's Jon Hamilton reports, researchers say there's no evidence that it's harmful.
JON HAMILTON: Nora Volkow is a brain researcher and director of an NIH institute. She was intrigued by this possibility, for personal as well as professional reasons.
NORA VOLKOW: I'm also seeing many of my relatives and friends spending hours on their cell phones. And the question in my brain is: Could this have any effect?
HAMILTON: Volkow knew that some MRI scanners produce electrical and magnetic fields powerful enough to cause brain cells to consume more energy in the form of glucose.
VOLKOW: Glucose metabolism goes up when you activate your brain, when you're thinking, when you're speaking, because you need the energy source in order for cells to function.
HAMILTON: She wanted to know whether the electromagnetic fields produced by cell phones were strong enough to affect glucose metabolism in the brain cells the same way a scanner can. So she and a team of researchers studied 47 people.
VOLKOW: We put two cell phones - one in the left ear, one in the right ear.
HAMILTON: Then the researchers activated the phone on one side and used a PET scanner to measure how much glucose was being consumed by brain cells. Volkow says a 50- minute call boosted brain metabolism.
VOLKOW: There was an overall increase, approximately 6 to 8 percent, but only on the areas of the brain that were close to the antenna.
HAMILTON: Volkow says that increase in brain metabolism is not terribly dramatic. Studies have shown that just opening your eyes can produce a much greater change in brain cells that process visual information.
VOLKOW: Based on this finding, I cannot say: Is this bad that you're increasing glucose metabolism? Or could it be good?
HAMILTON: Some researchers say the study offers more questions than answers.
LENNART HARDELL: What about long-term use, and what about children and young persons?
HAMILTON: Lennart Hardell, a cancer researcher in Sweden, co-wrote an editorial accompanying the study.
HARDELL: There are many questions which are now raised from this very, very important study.
HAMILTON: Steven Novella, a neurologist at Yale, thinks even an indirect link is unlikely. He says almost everything affects metabolism.
STEVEN NOVELLA: You know, if you go into a warmer room, your metabolism will increase. And, in fact, you know, the authors were speculating somewhat about how much of this increase they measured could be due just to the fact that the phone is warm and it warms up the tissue.
HAMILTON: The authors agree with Novella that there's no reason to think the changes they noticed would increase anyone's risk of cancer. And Novella says there's not much reason to worry about other health risks either. He says reassuring results from several large international studies have found that if there is any risk from cell phone radiation, if must be very small.
NOVELLA: If you want to minimize even the small remaining risk that is still there, you could do things like, you know, use a landline when one is available rather than your cell phone, or you can, you know, use the phone on speakers, that you're holding it away from your head rather than up against your ear.
HAMILTON: Jon Hamilton, NPR News.
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