Researchers call for greater caution, but skeptics say the evidence from rat studies is not convincing
Does cell phone radiation cause cancer? New studies show a correlation in lab rats, but the evidence may not resolve ongoing debates over causality or whether any effects arise in people.
The ionizing radiation given off by sources such as x-ray machines and the sun boosts cancer risk by shredding molecules in the body. But the non-ionizing radio-frequency (RF) radiation that cell phones and other wireless devices emit has just one known biological effect: an ability to heat tissue by exciting its molecules.
Still, evidence advanced by the studies shows prolonged exposure to even very low levels of RF radiation, perhaps by mechanisms other than heating that remain unknown, makes rats uniquely prone to a rare tumor called a schwannoma, which affects a type of neuron (or nerve cell) called a Schwann cell.
The studies are notable for their sizes. Researchers at the National Toxicology Program, a federal interagency group under the National Institutes of Health, tested 3,000 rats and mice of both sexes for two years—the largest investigation of RF radiation and cancer in rodents ever undertaken in the U.S. European investigators at the Ramazzini Institute in Italy were similarly ambitious; in their recent study they investigated RF effects in nearly 2,500 rats from the fetal stage until death.
Also noteworthy is that the studies evaluated radiation exposures in different ways. The NTP looked at “near-field” exposures, which approximate how people are dosed while using cell phones. Ramazzini researchers looked at “far-field” exposures, which approximate the wireless RF radiation that bombards us from sources all around us, including wireless devices such as tablet and laptop computers. Yet they generated comparable results: Male rats in both studies (but not mice or female animals) developed schwannomas of the heart at statistically higher rates than control animals that were not exposed.
Taken together, the findings “confirm that RF radiation exposure has biological effects” in rats, some of them “relevant to carcinogenesis,” says Jon Samet, a professor of preventive medicine and dean of the Colorado School of Public Health, who did not participate in either study. Samet, however, cautioned the jury is still out as to whether wireless technology is similarly risky to people. Indeed, heart schwannomas are exceedingly rare in humans; only a handful of cases have ever been documented in the medical literature.
When turned on, cell phones and other wireless devices emit EF radiation continually, even if they are not being actively used, because they are always communicating with cell towers. The dose intensity tails off with increasing distance from the body, and reaches a maximum when the devices are used next to the head during phone calls or in front of the body during texting or tweeting..
Launched at the U.S. Food and Drug Administration’s request 10 years ago, the NTP study dosed rats and mice of both sexes with RF radiation at either 1.5, 3 or 6 watts of radiation per kilogram of body weight, or W/kg. The lowest dose is about the same as the Federal Communications Commission’s limit for public exposure from cell phones, which is 1.6 watts W/kg. The animals were exposed nine hours a day for two years (about the average life span for a rat), and the exposures were cranked up steadily as the animals grew, so the absorbed doses per unit body weight remained constant over time.
Initially leaked in 2016, results from that $25-million study provided the most compelling evidence yet that RF energy may be linked to cancer in lab rodents. The strongest finding connected RF with heart schwannomas in male rats, but the researchers also reported elevated rates of lymphoma as well as cancers affecting the prostate, skin, lung, liver and brain in the exposed animals. Rates for those cancers increased as the doses got higher but the evidence linking them with cell phone radiation specifically was weak by comparison, and the researchers could not rule out that they might have increased for reasons other than RF exposure. Paradoxically, the radiation-treated animals also lived longer than the nonexposed controls. The study results were reviewed by a panel of outside experts during a three-day meeting that ended on March 28.
They concluded there was “clear evidence” linking RF radiation with heart schwannomas and “some evidence” linking it to gliomas of the brain.
It is now up to the NTP to either accept or reject the reviewer’s conclusions. A final report is expected within several months.
Limited to rats only, the Ramazzini study tested three doses expressed as the amount of radiation striking the animal’s bodies: either 5, 25 or 50 volts per meter. The exposure measures therefore differed from the absorbed doses calculated during the NTP study. But the Ramazzini scientists also converted their measures to W/kg, to show how the doses compared with RF limits for cell phones and cell towers set by the FCC and the International Commission on Non-Ionizing Radiation Protection; they ranged down to a 1,000 times lower. The exposures began when the rats were fetuses and continued for 19 hours a day until the animals died from natural causes.
As in the NTP study, Ramazzini investigators detected statistically elevated rates of heart schwannomas in male rats at the highest dose. They also had weaker findings linking RF exposure to cancer of glial cells in the brain, which were limited to females. Ronald Melnick, a retired NTP toxicologist who designed the NTP study, says a measure of consistency between the two studies is important, because “reproducibility in science increases our confidence in the observed results.”
Just why Schwann and glial cells appear to be targets of cell phone radiation is not clear. David Carpenter, a physician who directs the Institute for Health and the Environment at the University at Albany, S.U.N.Y., explained the purpose of these cells is to insulate nerve fibers throughout the body. These are electrical systems, so that may be some sort of factor, he wrote in an e-mail. “But this is only speculation.”
In a February 2 statement, Jeffrey Shuren, director of the FDA’s Center for Devices and Radiological Health, wrote that despite the NTP study’s results, the combined evidence on RF exposure and human cancer—which by now amounts to hundreds of studies—has “given us confidence that the current safety limits for cell phone radiation remain acceptable for protecting the public health.” Chonock says that for him, evidence from the Ramazzini study does not alter that conclusion. “We continue to agree with the FDA statement,” he says.