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.