Cell phones have not been convincingly linked to brain cancer, but that doesn't mean that their associated radiation has no effect on our bodies. A new study shows that these pervasive devices can alter the brain's glucose metabolism, a marker of neuronal activity. The findings will be published in the February 23 issue of JAMA, Journal of the American Medical Association.

A team of researchers examined the minute effects of cell phones on the brains of 47 healthy human subjects. The volunteers had a Samsung Knack flip phone secured over each ear for 50 minutes before undergoing PET (positron emission tomography) scans at the Brookhaven National Laboratory in New York. In one 50-minute session, both phones were turned off, but in the other session, the right-ear phone was on and silently receiving a signal.

Nora Volkow, of the National Institutes of Health and co-author of the new study, and her colleagues found that although overall brain glucose metabolism didn't vary between "on" and "off" assays, "metabolism in the region closest to the antenna was significantly higher [about 7 percent] for on than off conditions." That region includes the orbitofrontal cortex and temporal pole, which are responsible for decision-making and auditory processing, respectively.

The 7 percent increase might actually be on the low end of the spectrum of what people experience after a lengthy phone conversation, Henry Lai, of the Department of Bioengineering at the University of Washington, Seattle, and Lennart Hardell, of the Department of Oncology at the University Hospital, in Örebro, Sweden, noted in an editorial in the same issue of JAMA. Because the phones in the "on" condition in the study were set on mute and only receiving a transmission, they were "actually emitting less radiofrequency radiation than is the case when a user is speaking into a phone, and the effect observed could thus potentially be more pronounced in normal-use situations," they noted.

They also pointed out that it's unlikely heat from the active phones was to blame for the changes in brain activity.

Although "these results provide evidence that the human brain is sensitive to the effects of [radiofrequency-modulated electromagnetic fields] from acute cell phone exposure," the long-term consequences of this slight shift—if there are any—remain unclear, concluded Volkow and her team. Previous research has even shown a boost in responsiveness during psychological testing after being subjected to cell phone radiation.

Some researchers and concerned individuals still doubt that cell signals are in the clear health-wise, but radiation frequencies, such as UV and x-rays, that are linked to cancer put out much stronger signals than do cell phones. And even though U.S. and European cell phone use has skyrocketed in the past decade, a five-year study published in December 2009 in the Journal of the National Cancer Institute found that rates of brain tumors in the connected countries of Northern Europe remained steady.

In the real world, phones aren't only planted against our ears, so it's also possible that radiofrequency emissions "might have effects on other organs leading to unwanted physiological responses," Lai and Hardell noted. Cell phones can generate low frequency electromagnetic fields, the lower frequencies of which have been shown to be "biologically active." 

But just what the impacts of these emissions might be—and how they are manifesting at a cellular level in humans—remain to be seen. Animal and in vitro experiments have shown that radiofrequency-modulated electromagnetic fields exposure can have an effect on cell membrane permeability, cell excitability or neurotransmitters, the researchers noted. Volkow and her colleagues emphatically left cancer out of the equation, concluding that the newfound brain changes "provide no information" about purported "carcinogenic effects" of too much cell chatter.

Image courtesy of iStockphoto/Magaiza