Radiation from cellphones may be linked with tumor development among male rats, according to new research—but the findings should not be extrapolated to humans, health officials said, noting that if there is any cancer risk associated with cell phone use, it's minimal.
The findings, which were released earlier this month for peer review and public comment, aim to inform future cellphone technology, Reuters reports. The two studies will be externally reviewed at the end of March. The research cost $25 million and was conducted over a decade, making it the most extensive assessment of the issue to date, according to the New York Times.
For the studies, researchers at the National Toxicology Program (NTP) investigated the effects of cell phone radiation exposure in rats and in mice. NTP is part of NIH's National Institute of Environmental Health Sciences. The researchers used the type of radiation emitted by 2G and 3G networks, which are used for voice calls and text messages in the United States. The researchers did not look into 4G, 4G-LTE, and 5G networks, which are used for functions such as video streaming.
Rodents in the studies were exposed to radio frequencies for up to two years. For nine hours daily, the animals were bathed in radiation for 10 minutes and then had a 10-minute break. Overall, the lowest level of radiation for rats was 1.5 watts per kilogram of body weight—roughly the same as the maximum amount of radiation exposure permitted for humans, NTP said—and 2.5 watts per kilogram for mice. On the high end, the maximum level of radiation was 6 watts per kilogram for rats and 10 watts per kilogram for mice.
For context, John Bucher, senior scientist at NTP, explained that researchers "studied the maximum that one could achieve during a call in a poorer-connection situation [when a cellphone has to work harder to establish connection] ... over nine hours a day for two years." He continued, "This is a situation, obviously, that people are not going to be encountering in utilizing cell phones. It's a situation that allows us to find a potential biological event if one is going to occur."
NTP in a statement found "little indication of health problems" in the mice studied. However, researchers observed male and female rats that were exposed to radiation were more likely to experience cardiomyopathy, which leads to heart tissue damage. Bucher said if the results are confirmed, they appear to suggest such radiation could be a "weak" carcinogen.
Further, male rats that received the highest radiation exposure had a 6% incidence rate of malignant tumors in the tissue covering the heart, compared with none among control groups, who were not exposed to radiation. Female rats did not experience a higher incidence of the tumors, known as schwannomas. Bucher said the effect occurred in males likely because they are larger and absorbed more radiation.
In addition, while rats and mice exposed to radiation had a higher incidence of tumors in the adrenal gland, brain, liver, pituitary gland, prostate, and pancreas, the researchers could not determine if the tumors were related to radiation exposure. The researchers also noted that rats had lower birth weights when their mothers were exposed to high levels of radiation during pregnancy and while nursing, though such rats eventually grew to normal size.
One odd finding, according to the researchers, was that rats exposed to radiation lived longer than those that were not. The researchers did not have a definitive explanation for the finding, according to the Los Angeles Times' "Science Now," though they suggested it could be related to radiation's potential to reduce inflammation. That said, they also acknowledged that the longer lifespan could be a coincidence.
Between the inconsistent findings, the use of non-human subjects, and the high level of radiation used, Bucher said the findings could not be extrapolated to health effects in humans. "At this point we don't feel that we understand enough about the results to place a huge degree of confidence in the findings," Bucher said. "I have not changed the way I use a cellphone."
American Cancer Society CMO Otis Brawley in a blog post said, "These draft reports are bound to create a lot of concern, but in fact they won't change what I tell people: the evidence for an association between cellphones and cancer is weak, and so far, we have not seen a higher cancer risk in people." Brawley added that if people are concerned about the findings, they could use an earpiece.
Jeffrey Shuren, director of FDA's Center for Devices and Radiological Health, acknowledged that the study had unusual findings and that his team is continuing to review them, though he stressed that available scientific information leads FDA to believe cellphone radiation does not present an adverse health effect for humans. "Even with frequent daily use by the vast majority of adults, we have not seen an increase in events like brain tumors," he said. "Based on this current information, we believe the current safety limits for cellphones are acceptable for protecting the public health."
However, some believed the ambiguity in the findings was concerning, according to the New York Times. Joel Moskowitz, director of the Center for Family and Community Health at the School of Public Health at the University of California, Berkeley, said based on the results, the government should reevaluate and tighten limits on cellphone radiation emissions (Kaplan, "Science Now," Los Angeles Times, 2/2; Steenhuysen, Reuters, 2/2; Eunjun Cha, "To Your Health," Washington Post, 2/2; Grady, New York Times, 2/2; Bankhead, MedPage Today, 2/2).
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