An international study that is the largest yet to focus on mobile-phone use and certain types of brain cancer didn’t find a conclusive link, researchers said.
The study of more than 10,000 people found that most use didn’t raise the risk of developing two types of tumors, according to results in the International Journal of Epidemiology. There was a “suggestion” that the heaviest mobile phones use may be tied to gliomas, a form of brain malignancy, the authors said. That data, though, was flawed, the authors concluded, saying that more study would be needed to establish a definitive link.
The report by the World Health Organization’s International Agency for Research on Cancer is the latest in a series of conflicting studies exploring whether a connection exists between mobile phones and cancer. Most have failed to identify a link. The debate has turned on the fact that the phones emit radio waves and, at higher levels than that released by phones, the emissions heat body tissue and spur tumors, according to the National Cancer Institute’s website.
“An increased risk of brain cancer is not established,” said Christopher Wild, director of the International Agency for Research on Cancer, in a statement. More studies are needed to definitely rule out a link in the heaviest mobile-phone users to malignancy, the researchers said.
The study participants included 5,117 patients who had either a meningioma, a slow-growing brain tumor, or glioma, a deadly type of brain tumor. They were matched with comparison subjects who didn’t have brain cancer, and all were questioned on their mobile phone use.
Researchers found “suggestions” of a 40 percent higher risk of glioma in those who were in the top 10 percent for the longest cumulative call time, the study authors said. That risk was greatest in people with brain cancer who reported that they often held their phones on the same side of their head as their gliomas developed, the authors said.
The higher cancer risk seen in heaviest users may not be a reliable finding because it was based on the amount of time people remembered talking on their phones, according to the study. Brain tumors can confuse thinking and affect memory, which could influence the results. Researchers said a higher proportion of people with gliomas were judged by their interviewers to have poor memory.
“It’s still too early to say if there is a higher risk because cancer, particularly brain cancer, can take years to develop,” often longer than the 10 years of phone use in some participants of the WHO study, said Henry Lai, a bioengineering researcher at the University of Washington in Seattle, in a telephone interview. Lai, who has studied mobile phone safety, wasn’t involved in the WHO research.
“It’s not beyond the realm of possibility that there’s a link” between mobile phone use and cancer, said Peter Inskip, senior investigator at the National Cancer Institute in Bethesda, Maryland.
More study is needed to look at a possible link between brain cancer and growing use of mobile phones by children, Inskip said. “What we might have considered heavy use 10 years ago might not be considered heavy use now,” he said.
People in the study reported spending a median time of 2 to 2.5 hours a month on their mobile phones, the study said. The heaviest users -- about 10 percent of the total -- said they spent 1,640 cumulative hours on the phone. Participants reported their use for periods ranging from one year to more than 10 years, according to the research.
The study’s findings show little or no risk of brain tumors for most long-term users of cell phones, the U.S. Food and Drug Administration said today in a statement.
“There are still questions on the effect of long-term exposure to radio frequency energy that are not fully answered” by the WHO study, Abiy Desta, network leader for science at the FDA’s Center for Devices and Radiological Health, said today in the statement. “However, this study provides information that will be of great value in assessing the safety of cell phone use.”
The FDA has the authority to require manufacturers to notify consumers and repair, replace or recall mobile phones if they are ever found to emit radiofrequency energy at a hazardous level, according to a fact sheet on the agency’s website.
“Today, mobile phone use has become much more prevalent, and it is not unusual for young people to use mobile phones for an hour or more a day,” the WHO researchers said in a statement. The increased use is partially offset by younger people’s preference for hands-free calling, texting over phone calls and lower emissions of some newer phones, the researchers said.
The study’s findings “are consistent with conclusions reached in an already large body of scientific research on this subject,” John Walls, a spokesman for CTIA-The Wireless Association, a Washington-based trade group for the wireless industry, said today in a statement.
More than one-third, or $6.8 million, of the study’s $23.7 million cost came from the mobile-phone and other industry sources, according to a news release from the World Health Organization. The researchers came from 13 countries, including Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden and the U.K. No one was involved from the U.S.
The number of wireless accounts grew to 285.6 million in December from 109.5 million in 2000, according to CTIA. The number of U.S. households that only have wireless phones was almost 23 percent in December, up from 8.4 percent in 2005, the CTIA said.
Previous studies include a December report by investigators from the U.S. National Cancer Institute using cancer registries in Denmark, Finland, Norway and Sweden, covering more than 16 million adults, to track the number of people diagnosed with brain tumors since 1974, when mobile phone use in those countries began seeing widespread use. The researchers found no surge in brain cancer cases.
A study of 420,000 Danish people who used mobile phones for an average of 8.5 years, reported in December 2006, also found no increase in cancers.
Ramon Llamas, a phone-industry analyst at Framingham, Massachusetts-based International Data Corp., suggested studying the use of mobile phones going forward was a moving target.
“No one wants to do something that endangers their health, but consumer behavior on mobile phones is changing dramatically already,” Llamas said in an interview. “Every carrier has seen a dramatic change toward people texting and using data more, which brings the phone away from the ear.”
The newest study “illustrates how difficult it is to identify and corroborate, or definitively rule out, any possible association,” said John E. Niederhuber, director of the U.S. National Cancer Institute.