Two long-awaited studies of how cellphone radiation affects the health of mice and rats, released yesterday, are giving scientists plenty to think about—but the findings won’t resolve the decades-old uncertainty surrounding the issue.
The voluminous but sometimes puzzling results also aren’t likely to prompt U.S. agencies or other bodies to immediately change how they regulate the ubiquitous devices or view their health risks.
Questions about whether cellphones harm health have persisted for decades. The devices emit nonionizing, electromagnetic radiation of the sort that heats food in a microwave oven, but scientists have struggled to conclusively link cellphone use to cancers or other illnesses.
In a bid to clarify matters, the U.S. Food and Drug Administration (FDA), which plays a key role in developing U.S. cellphone regulations, asked the National Toxicology Program (NTP) at the National Institutes of Health to launch studies examining the issue. Yesterday, NTP released two studies conducted as part of a $25 million research program.
In the studies, which lasted 2 years, rats and mice of both sexes ran freely in specially constructed reverberation chambers where their entire bodies were exposed to radiation. The levels ranged from a low of 1.5 watts per kilogram to a high of 10 watts per kilogram, and exposures were limited to the 2G and 3G frequencies, which are still widely used for voice calls and texting. In general, the animals were exposed to radiation levels that either matched or exceeded what’s permissible under current U.S. regulations.
Exposures began during pregnancy and then continued 9 hours a day for 2 years, “which is not a situation that most people will encounter when using cellphones,” said John Bucher, a senior scientist at NTP in Durham, North Carolina, who co-directed the study. “Though it does allow us to explore the potential for biological effects if they’re going to occur.”
The study’s strongest finding was that male rats had an elevated risk of developing tumors, called malignant schwannomas, in the connective tissues surrounding nerves in the heart. Sex- and species-dependent increases were also observed for lymphoma, as well as cancers of the prostate, skin, lung, liver, and brain, but these findings were weaker by comparison and possibly due to causes other than radiation. Similarly, the researchers observed noncancerous health effects—including lower birth weights, evidence of DNA damage, and heart conditions—among exposed rats, although it was not always clear whether the conditions were caused by radiation exposure.
In a counterintuitive result, male rats and mice exposed to radiation lived longer, and had lower levels of age-related kidney disease, than males not exposed to radiation.
Early reactions to the findings suggest they will not dramatically reshape the debate over cellphone safety. Both critics and supporters of current risk evaluations and safety standards claim the studies support their points of view.
The new findings are “incredibly important,” says David Carpenter, a public health physician at the State University of New York in Albany who has long warned of cellphone dangers. “I think this is the first clear evidence showing that these sorts of radiofrequency fields increase risks for all kinds of cancer,” he says, noting that malignant schwannomas have been detected in previous human studies of cellphone risk. He believes that more of the associations between radiation exposure and rodent disease could have reached statistical significance had the study included a larger number of animals.
Jonathan Samet, who led a prominent international scientific panel that concluded that cellphone radiation was a “probable” human carcinogen, predicts the new studies won’t “nudge that classification in one direction or another.” The panel led by Samet, dean of the Colorado State University School of Public Health in Fort Collins, was organized by the International Agency for Research on Cancer, a specialized agency of the World Health Organization.
The findings don’t suggest that U.S. regulations on cellphone radiation need to be tightened, said Jeffrey Shuren, director of FDA’s Center for Devices and Radiological Health in Silver Spring, Maryland, in a statement. The new studies, when combined with previous research, have “given us the confidence that the current safety limits for cellphone radiation remain acceptable for protecting the public health.”
Bucher, who helped lead the new studies, says he has no intention of changing his cellphone habits.
In a statement, the U.S. National Cancer Institute noted that “often, when concerns are raised about exposures that may confer low-level risk for a rare cancer outcome—as is the case for cellphones and brain tumors—it takes time and many studies to come to a conclusion based on the weight of the evidence.” It notes that a major European study of cellphones and brain tumor risk is expected to report results later this year.
Meanwhile, external experts are scheduled to review the new NTP studies at a meeting in late March. NTP also plans to continue its animal studies in new chambers that replicate the radiation produced by the current generation of 4G cellphones.