Using a cell phone seems to increase the rate of sugar breakdown in the area of the brain closest to the phone antenna, which is a sign of heightened brain activity, a new study finds.

But researchers don't know if this increased brain activity has any effect on cancer risks or other health risks, said Dr. George Kunos, scientific director of the National Institute on Alcohol Abuse and Alcoholism, who directs the research program that provided funding for the study.

When people in the study put a muted cell phone to their ears for 50 minutes, they had 7 percent higher rate of glucose breakdown in one area of the brain than when they put a turned-off cell phone to their ears.

Glucose breakdown in the brain "simply indicates that neurons are active," Kunos told MyHealthNewsDaily. "It doesn't tell what that activity is for, or what the molecular mechanisms are it's a rather nonspecific signal."

The researchers found no difference in glucose breakdown in the brain as a whole, suggesting other areas were compensating for the increase.

The study will be published tomorrow (Feb. 23) in the Journal of the American Medical Association.

Interpreting brain activity

Brain activity is not something to be afraid of it happens all the time, Kunos noted. For example, if you open your eyes and see something, there is activity in the visual cortex, he said. The same goes for the auditory cortex when you listen to music.

To measure the effects of cell-phone use on brain activity, study researcher Dr. Nora D. Volkow, of the National Institutes of Health, asked 47 study participants to hold two cell phones one to each ear for 50 minutes.

The researchers viewed the participants' brain activity using positron emission tomography (PET) scans on two different days, the study said. On one day, the cell phones were on but set on mute; on the other day, the cell phones were off.

There was 7 percent more glucose metabolism in brain regions closest to the phone antenna when the cell phones were on mute, compared with when the phones were off, the study said.

Because the phones were on mute, researchers can rule out that the increase in brain activity was from talking to someone on the phone, Kunos said.

The result "shows that there are effects at lower levels of radiation" that come from cell phones, said Dr. Lennart Hardell of University Hospital in Sweden, who wrote an editorial that accompanied the study.

Although this study looked at glucose metabolism, the findings could mean other biochemical processes in the brain also are affected, Hardell said.

"Much more research is needed to understand the health consequences, if any," Hardell told MyHealthNewsDaily.

Questions raised

The study raises important questions about long-term cell phone use, said epidemiologist Devra Davis, founder of the Environmental Health Trust in Wyoming, who was not involved with the study.

"This is a very important study, not because it resolves a lot of questions but because it forces us to ask questions we have not wanted to ask," Davis, formerly of the University of Pittsburgh, told MyHealthNewsDaily.

Researchers need to investigate the effects of an elevation in the brain's glucose metabolism in both the short term and long term, as well as what happens if the metabolism remains elevated for a long time, she said.

"Cells proliferate at a faster rate in the presence of glucose, and proliferation is what you don't want when things are malignant," said Davis, who also wrote a book on cell-phone safety called "Disconnect" (Dutton; 2010).

More research is needed to see the possible effects of continuously increased metabolism on diseases such as Alzheimer's and cancer , she said.

Past evidence

The cancer-causing radiation emitted from X-rays, called ionizing energy, is different from the radiofrequency radiation from cell phones, which is non-ionizing, according to the National Cancer Institute.

Past research investigating the relationship between cell phones and cancer has yielded mixed results. A 2001 study in the New England Journal of Medicine showed that people who used cell phones didn't have a higher risk of brain tumors than people who didn't use cell phones. But a 2008 study in the American Journal of Epidemiology showed that heavy cell phone users had a 50 percent higher risk of salivary gland cancer than people who didn't use cell phones.

A study published this month in the journal Bioelectromagnetics showed that cell-phone use was not associated with an increased risk of developing brain tumors .

It is unlikely that cell phones cause brain cancer, because there is just not enough energy to directly damage DNA, said Frank de Vocht, author of the Bioelectromagnetics study and a lecturer in occupational and environmental health at the University of Manchester in England.

"There may, however, be other, more subtle ways in which it [cell-phone use] may affect carcinogenesis for example, being a cancer-promoting factor or [affecting] the immune system," de Vocht told MyHealthNewsDaily.

It's possible that high cell phone use could increase cancer or other health risks among certain people, he said.

Pass it on: Using a cell phone for 50 minutes can increase brain glucose metabolism by 7 percent. But it's unknown what the long-term effect of this increase in metabolism means for health or cancer risks.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.