Oct. 20, 2011 -- In recent years, people have been whipsawed by conflicting studies about the risks posed by low levels of radiation given off by cell phones.
Now, one of the largest and longest-running studies ever to look for a link between mobile phone use and brain tumors shows that cell phone use doesn't increase the risk of brain cancer and other kinds of central nervous system cancers.
The study was conducted in Denmark, a country that's unique because it keeps extraordinary health records on its residents. It's published in the journal BMJ.
Researchers used the country's detailed databases to find out if adults with cell phone contracts before 1995 got brain tumors more frequently that those who didn't subscribe to mobile services.
Because the study stretches back decades, researchers say many of these subscribers were probably using early-generation cell phones that emitted more radiation than newer phones.
Over an 18-year period, 10,729 cancers of the brain and central nervous system were diagnosed;9,883 of these were in 3.2 million Danes in the general population who were thought not to use cell phones and 846 were diagnosed in 358,403 people with cell phone contracts.
The risk of getting a brain tumor was essentially no different between the two groups.
That remained true even when researchers looked just at adults who'd had cell phones contracts the longest, for more than 13 years, and when researchers looked at specific tumor types.
"We didn't find any association," says researcher Patrizia Frei, PhD, who was a postdoctoral research fellow at the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen when the study was conducted.
So, Cell Phones Safe or Not?
Federal health agencies, including the FDA, CDC, and National Cancer Institute, have stated that the balance of the evidence shows that cell phones probably don't cause any health problems.
But because so many people use them -- more than 87% of the U.S. population had a mobile phone in 2008 -- these agencies also agree that more research is needed.
In May, a panel of experts convened by the World Health Organization reviewed the evidence and ruled that radiation from cell phones could "possibly" cause cancer, putting the risk posed by cell phones on par with pesticides, some food dyes, and heavy metals.
Jonathan Samet, MD, a professor of preventive medicine at the University of Southern California's Keck School of Medicine, in Los Angeles, who led that panel, says these new findings wouldn't have changed their ruling.
"While this study does not show any association, it does not establish "safety" -- that is, the absence of risk," Samet says in an email. "This is a useful addition to the literature, and we need more studies of high quality."
Swiss researchers who wrote an editorial on the study said it had important strengths that should further reassure cell phone users.
Perhaps the biggest advantage was because it used large databases, the study did not need to rely on people to remember details about their cell phone use. Faulty memory can be a major source of inaccurate information in studies.
Why More Research Is Needed
One weakness, though, was that the study used mobile phone contracts as a way to estimate use.
Just having a cell phone contract doesn't mean a person is using a phone regularly, and some people who don't have contracts will have pay-as-you-go phones.
"The resulting misclassification would dilute any association between mobile phone use and cancer risk, and this is important for a ... study like the current one," says Anders Ahlbom, professor of environmental medicine at Karolinska Institute in Stockholm, Sweden, in an editorial.
Researchers agree that this study should not be the final word.
"Our study can't answer all the questions," says Frei. For example, she says questions remain about risks associated with continued long-term use of cell phones, for longer than 20 years. And there's been little information about the use of cell phones in children, she says.
"We couldn't say that we've solved all the problems so far. I would still say that we have some limited evidence," she says.
For another perspective on the cell phone debate, read the commentary of Children's Health blogger Roy Benaroch.