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PHILADELPHIA (CNN) — The evidence is more clear that there is a link between cancer and cell phone radiation, the National Institutes of Health said Thursday.

“The National Toxicology Program (NTP) concluded there is clear evidence that male rats exposed to high levels of radio frequency radiation (RFR) like that used in 2G and 3G cell phones developed cancerous heart tumors,” the agency said in a statement. The conclusion comes from a final report on research evaluating the effect of radio frequency radiation, which is used in cell phones. “There was also some evidence of tumors in the brain and adrenal gland of exposed male rats. For female rats, and male and female mice, the evidence was equivocal as to whether cancers observed were associated with exposure to RFR.”

The report matches a draft that was released in February.

What is surprising, however, is that another federal health agency, the US Food and Drug Administration, disagrees with the conclusion.

“After reviewing the study, we disagree, however, with the conclusions of their final report regarding ‘clear evidence’ of carcinogenic activity in rodents exposed to radiofrequency energy,” Dr. Jeffrey Shuren, director of the FDA’s Center for Devices and Radiological Health, said in a statement Thursday in response to the report.

One thing the two agencies, which both fall under the US Department of Health and Human Services, agree on is that the findings of these studies in rats and mice should not apply to human cell phone use.

“The exposures used in the studies cannot be compared directly to the exposure that humans experience when using a cell phone,” John Bucher, a senior scientist with the National Toxicology Program, said in a statement. “In our studies, rats and mice received radiofrequency radiation across their whole bodies. By contrast, people are mostly exposed in specific local tissues close to where they hold the phone. In addition, the exposure levels and durations in our studies were greater than what people experience.”

The final report and the consensus from the National Toxicology Program are the conclusion of a 10-year, $30 million research effort.

The research included two large animal studies — one in rats and one in mice — that link high levels of cell phone radiation to some evidence of carcinogenic activity in male rats, including a rare type of tumor called a schwannoma in their hearts. There were no such significant findings in the female rats.

Similarly, no significant findings emerged in the mouse study, according to the reports.

“One of the things that we found most interesting about our findings was that the malignant schwannomas — even though they occurred in the heart and not in the head of these animals — were in fact schwannomas,” Bucher said in February when the draft report was released.

The FDA notes that cell phones emit low levels of radiofrequency energy that are non-ionizing and thus not considered strong enough to permanently damage biological tissue including DNA.

NIH also noted that the studies did not evaluate the current 5G networks that are used or Wi-Fi. “5G is an emerging technology that hasn’t really been defined yet. From what we currently understand, it likely differs dramatically from what we studied,” said Michael Wyde, a lead toxicologist on the studies.

Confusion and controversy

The National Toxicology Program studies involved about 3,000 rodents, as was detailed in the February draft report.

The animals were exposed to radio-frequency radiation levels equal to and higher than the highest level currently allowed for mobile phone emissions. The researchers tracked the health of the animals from in utero to 2 years of age.

A 2-year-old rat would be somewhat comparable to a 70-year-old human, Bucher said.

The researchers divided the rodents into two groups based on radiofrequency radiation levels, low or high, and exposed their entire bodies to radiofrequency radiation for 10-minute increments totaling to about nine hours a day over the two-year period.

“It’s important to consider the magnitude of the exposures to the animals in these studies in relation to what one might typically receive from using a cell phone,” Bucher said. “The lowest energy level of the radiofrequency radiation we studied was similar to the highest level currently permitted for cell phone emissions.”

Among the male rats, the researchers found tumors in about 6% of those in the highest radiation exposure group, Bucher said. That percentage “exceeded the mean historical incidence (0.8%), and exceed the highest rate observed in a single historical control group (2%) of completed peer reviewed studies,” the researchers wrote.

The researchers also found that the male rats in the high-exposure group appeared to live longer than the other rats, but more research is needed to determine why and how that may be relevant to the study results.

“Animal studies like this one contribute to our discussions on this topic, but we must remember the study was not designed to test the safety of cell phone use in humans, so we cannot draw conclusions about the risks of cell phone use from it,” Shuren said.

“Based on our ongoing evaluation of this issue, the totality of the available scientific evidence continues to not support adverse health effects in humans caused by exposures at or under the current radiofrequency energy exposure limits. We believe the existing safety limits for cell phones remain acceptable for protecting the public health.”

‘Exercise caution’

“The safety of consumers is the wireless industry’s first priority,” CTIA, the trade association representing the US wireless communications industry, said in a statement Thursday. “We follow the guidance of experts when it comes to cellphones and health effects. The scientific community will consider today’s report in the context of the many scientific studies conducted over several decades.

“We note NTP’s own assessment that today’s report cannot be extrapolated to human cell phone usage, and the Food and Drug Administration’s concurrence that ‘these findings should not be applied to human cell phone usage’ and that ‘the existing safety limits for cell phones remain acceptable for protecting the public health.’ These conclusions are consistent with official federal brain tumor statistics showing that since the introduction of cellphones in the mid-1980s, the rate of brain tumors in the United States has decreased.”

CNN’s parent company, WarnerMedia, is owned by communications company AT&T.

The Environmental Working Group, an advocacy organization, said in a statement Thursday that “the findings reinforce the need for people, especially children, to exercise caution when using cellphones and other radiation-emitting devices.”

Olga Naidenko, a senior scientist for chlidren’s environmental health at the group, said, “This report should raise alarms for policymakers and awareness for all Americans. These studies should have been done before more than 90 percent of Americans, including millions of children, started using this technology day in and day out.”

Joel Moskowitz, director of the Center for Family and Community Health at the University of California Berkeley’s School of Public Health, said in an email that the new report affirms the concerns of the scientific community about “harm caused by chronic exposure to low-intensity electromagnetic fields.”

Bucher was clear: “We believe that the link between radiofrequency radiation and tumors in male rats is real, and the external experts agreed.”

Shuren said the FDA will continue to evaluate scientific evidence that looks at the potential health effects of radiofrequency radiation on animals and humans.

So what’s a cell phone user to do? There are some steps people can take to limit exposure to radiofrequency radiation. These include holding phones away from your body and using earbuds or other means to communicate without holding the phone against your body.

“I have not changed the way I use a cell phone,” Bucher said.

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