This is the VOA Special English Health Report.

　　How important is your mobile phone, better known to Americans as a cell phone?

　　MAN: "I use my phone all the time. I'm always on my phone."

　　WOMAN: "It's kind of pretty much important to me because it's like my life saver."

　　WOMAN: "I need my cell phone."

　　So far, no studies have proven beyond question that the radio signals from cell phones cause brain cancer or other health problems. But a new study by government scientists in the United States has some people wondering what to think.

　　The scientists found that holding a cell phone to your ear for at least fifty minutes increases brain cell activity. Even the scientists themselves are not sure about the meaning of their findings.

　　Dr. Nora Volkow led the study. She heads the National Institute on Drug Abuse, part of the National Institutes of Health. Dr. Volkow says she would not be concerned that fifty minutes of cell phone exposure would harm anyone. But she says the research does show the need to study whether or not there are long-lasting effects of repeated exposure over several years.

　　Her team studied forty-seven healthy volunteers between January and December of two thousand nine. The volunteers had cell phones placed against both ears while the scientists made images of their brain activity.

　　As part of the test, one phone was activated but muted for fifty minutes. The other phone was off. After that, the people were tested with both phones turned off. Dr. Volkow says the brain scans showed increased activity in brain cells closest to the activated phone.

　　NORA VOLKOW: "This right area of the brain that was very close to the antenna shows the largest increase in metabolism as compared when the telephones were off. Even though the radio frequencies that are emitted from current cell phone technologies are very weak, they are able to activate the human brain to have an effect.''

　　The scans showed how the brain cells used sugar to produce energy, a normal activity. The activity was seven percent higher in areas of the brain closest to the cell phone antenna.

　　The study appeared in the Journal of the American Medical Association.

　　Experts say people who are concerned about mobile phones can take steps like using a hands-free device.

　　Dr. Giuseppe Esposito is a nuclear medicine expert at Georgetown University Medical Center in Washington. He says after many years of studies, better kinds of research are still needed to settle questions about cell phone safety. These studies would take years.

　　GIUSEPPE ESPOSITO: "We need what are called epidemiological studies where you will follow a population using cell phones -- high users or light users -- and then see what happens over the years."

　　And that's the VOA Special English Health Report. For more health news, go to www.unsv.com. You can also post comments on our website or on Facebook at VOA Learning English. I'm Steve Ember.