Do cell phones cause brain tumors? The question has been asked since the phones first arrived on the scene, and now one of the largest studies ever to examine the issue shows that the answer is no.
The new report is in line with most other large studies and should reassure the hundreds of millions of regular cell phone users around the world.
But questions remain about the safety of long-term cell phone use, since the studies reported to date have followed subjects for no more than a decade.
Other Brain Diseases
In the new study, researchers compared the cell phone usage histories of 966 patients with glioma-type brain tumors with 1,716 people without tumors matched for age, sex, and place of residence.
The four-year investigation included people living in urban and rural locations within England and Scotland. It is reported in the Jan. 21 issue of BMJ.
“This was a highly representative sample of the population of the U.K.,” researcher Patricia McKinney, PhD, tells WebMD.
However, it is not yet clear if the phones raise the risk of other brain and central nervous system diseases, says Christoffer Johansen, MD, PhD, who has long studied cell phone use along with colleagues from the Danish Cancer Society.
“What we can say is that we now know that people who have used mobile phones for 10 years or less do not seem to be at increased risk for the most commonly seen brain tumors,” he tells WebMD.
“But we don’t know very much about usage for more than 10 years, or whether or not mobile phones are associated with other brain diseases like Alzheimer’s and multiple sclerosis.”
Rural vs. Urban Users
People who reported using cell phones regularly had no greater overall risk of developing brain tumors then those who reported infrequent use, she says. Neither total years of cell phone use nor total hours of use were found to influence risk.
At least one previous study suggested that regular cell phone users in rural areas were more likely to develop brain tumors than city-dwelling cell phone users. But the U.K. study did not back this up.
Likewise, no increase in risk was seen among regular users of first-generation cell phones, which used high-power-emitting analog signals rather than digital signals.
There did appear to be an excess risk of brain tumors occurring on the same side of the head as the cellular phone was used on. But this was accompanied by a decrease in expected tumors on the opposite side of the head.
“We believe this is due to reporting bias, rather than being a real effect,” says McKinney, who is a professor of pediatric epidemiology at the University of Leeds.
“If people believed that mobile phones were responsible for their tumors they might overreport the use of the phone on the side on which the tumor developed.”
McKinney agrees that the long-term safety of regular cell phone use won’t be known until researchers have followed users for decades.
Johansen says his research team has followed a Danish group for close to 20 years and will soon report on their findings.
“There is still a lot we don’t know,” he says. “We will have to follow people for many more years.”
By Salynn Boyles, reviewed by Louise Chang, MD
SOURCES: Hepworth, S.J., BMJ, Jan. 21, 2006; vol 332, online edition. Patricia A. McKinney, PhD, professor of pediatric epidemiology, Center for Epidemiology and Biostatistics, University of Leeds, England. Christoffer Johansen, MD, PhD, head, department of psychosocial cancer research, Institute of Cancer Epidemiology, The Danish Cancer Society, Copenhagen, Denmark.