There is "some evidence" cellphones cause cancer in male rats, according to a National Toxicology Program (NTP) study that began in the 1990s—but the researchers—and FDA—cautioned that the results cannot be extrapolated to humans' cellphone use.
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About the study
The latest study marks the final report in a years-long research project that sought to test the effects of radio-frequency radiation used in 2G and 3G cellphones on around 3,000 rodents. For the study, researchers exposed rats and mice to radiation for nine hours a day for two years. The exposures started before birth until the rats were about two years old.
The rats were exposed to radiation at a frequency of 900 megahertz, which was typical of cellphones in the 1990s, when the study began, according to the New York Times. The lowest level of radiation the rats were exposed to was equal to the maximum level of radiation allowed by federal regulations, which rarely occurs in typical cellphone use, according to the NTP. The highest level the rats were exposed to was four times higher than the maximum allowed.
Cellphone radiation may cause cancer—in male rats
The researchers found that around 2% to 3% of male rats developed malignant gliomas, a form of brain cancer, while no rats developed such cancer in a control group that received no radiation. They also found "clear evidence" linking the radiation and malignant heart tumors, and "some evidence" linking radiation to adrenal-gland tumors.
However, the researchers noted these associations were only seen in male rats—there were no links to cancer among female rats or male or female mice, Live Science reports.
Result cannot 'be compared directly' to what humans use now, researcher warns
While the researchers argue that the results raise questions about how radio-frequency radiation affects health, they caution that the results hold no implications for humans' cellphone use.
John Bucher, a senior scientist at the NTP, said the researchers "believe that the link between radio-frequency radiation and tumors in male rats is real." However, he cautioned that the levels of radiation the rats were exposed to were significantly higher than those seen by typical cellphone users, and therefore cannot "be compared directly to the exposure that humans experience."
The researchers also noted that rodents in the study had their entire bodies exposed to radio-frequency radiation, where as humans only have limited exposure to areas where they hold their phones. The researchers also noted that the study, which launched in 1993, relied on now outdated technology. The researchers tested a level of frequency typically found in second-generation cellphones, the Times reports. Current cellphones are part of the fourth generation, and use higher frequencies that, according to scientists, are far less likely to penetrate the bodies of rats and humans.
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The NTP is currently working on smaller exposure chambers that will allow researchers to test newer devices quicker. The new studies will also focus on biomarkers, or physical signs, including DNA damage, which can be detected quicker than cancer.
In a statement, the director of the FDA's Center for Devices and Radiological Health, said the agency disagreed with the study's findings of "clear evidence" for heart schwannomas, but did not dispute the study's findings of "some evidence" for brain tumors—among male rats.
As far as his own takeaways, Bucher said he is now "a little more aware" of his cellphone usage. On longer calls, he said he tries to use earbuds or find another way "of increasing the distance" between his body and the cellphone (Broad, New York Times, 11/1; Fox, NBC News, 11/1; May, USA Today, 11/2; Rettner, Live Science, 11/1).
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