THURSDAY, Oct. 20 (HealthDay News) -- The 5 billion people worldwide who chat away on cell phones shouldn't worry about an increased risk of brain cancer, new Danish research contends.

One of the largest and longest studies on the subject finds no more brain tumors among people who had cell phones over 17 years than among people who had no cell phones.

Although no one study can rule out harm with absolute certainty, "the risk, if there is one, is extremely low," said Dr. Ezriel E. Kornel, director of the Neuroscience Institute at Northern Westchester Hospital in Mount Kisco, N.Y.

Previous studies haven't definitively answered the question of whether cell phone use is harmful: While several studies have found no cause for alarm, a handful did show an upped risk of malignant brain tumors.

Based on the totality of existing evidence, the World Health Organization in May classified cell phones as "possibly carcinogenic to humans," and placed them in the same category as the pesticide DDT and gasoline engine exhaust.

Experts have been concerned that radio frequency electromagnetic fields sent out by a cell phone held close to the ear could trigger a malignancy.

This new study, led by researchers from the Institute of Cancer Epidemiology in Copenhagen, was a follow-up to an earlier trial that also had found no increased risk in cell phone users. Their latest report is published in the Oct. 20 issue of BMJ.

Here, the researchers analyzed data on about 360,000 people in Denmark who had cell phone subscriptions.

There was no difference in tumor incidence between the two groups overall or for people who had had cell phones for 13 years or longer.

Nor was there any hint that tumors might be more common in areas of the brain closest to the ear where the cell phone is held.

There was a very slight increased risk of glioma, a type of malignant brain tumor, in men, but the difference virtually disappeared after five years.

"That might potentially mean that people who are genetically predisposed are at a greater risk by using cell phones but, over the years the effect washes out because people who were going to get tumors already got them," said Dr. Michael Schulder, vice chairman of neurosurgery at the Cushing Neuroscience Institute of the Hofstra North Shore-LIJ School of Medicine in Manhasset, N.Y.

One limitation of the new study is that the authors weren't able to look at how long or often people used their cell phones or if, in fact, they used them at all, Kornel noted.

Despite the findings, it's unlikely that the question of a link between brain cancer and cell phone use will be answered to everyone's satisfaction anytime soon.

In the meantime, there are some common-sense measures people can take to reduce any risk there might be.

"Rather than clamp the cell phone to the side of your head, use an earpiece with a wire," advised Schulder.

Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La., said, "If you're going to use a cell phone, I'd try to use it as little as you need to."

He added, though, that he did not believe that "the risks, if any, are very great."

But the biggest danger from cell phones may not be from brain cancer.

"The biggest risk incurred from cell phones is during driving," said Schulder. "If you studied 10 million people for 100 years, the risk from texting while driving, looking at emails, holding the phone with your hand to your head and probably, to some extent, even talking on the phone are all far greater than anything that might ever show up in a study like this."

More information

For more on brain cancer, visit the U.S. National Library of Medicine.