And there was also a "statistically significant" increase in the number of rats and mice with tumors in other organs - including the brain, prostate gland, liver and pancreas - but the researchers determined that the link between those and RFR was unclear. "The reports don't go much further than what we have reported earlier". Bucher emphasized that even the lowest levels used in the study were much higher than the maximum exposure even a frequent cellphone user would get. The toxicology program is headquartered at the National Institute of Environmental Health Sciences. Researchers exposed the rodents' entire bodies to the radiowaves for more than nine hours per day, for up to two years. While these tests aren't conclusive, they do suggest heightened exposure to radiation could induce certain forms of cancer.
Animals were exposed to radiofrequency radiation associated with the two most common types of cell phone networks: global system mobile communications (GSM) and code division multiple access (CDMA). The only frequencies used were 2G or 3G. But there was overall little difference in the actual health outcomes of exposed mice and rats compared to their untouched counterparts by the experiment's end - some control groups even died sooner than those exposed to the radiation.
The new reports are still considered drafts, and the NTP plans to have outside experts review them next month.
If radiofrequency radiation is indeed a carcinogen, Bucher said, it is likely a weak one.
Bucher, who helped lead the new studies, says he has no intention of changing his cellphone habits.
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The authors caution that while much more research is needed to find out whether or not the ways that average people use cell phones could raise cancer risks, the findings highlight an "area of concern".
Bucher said the finding of rat heart tumors does not translate directly to humans.
"We don't have any idea really", Bucher said.
EWG has been at the forefront of public interest organizations raising concerns about cellphone use and cancer.
The study produced some evidence of an increased incidence of brain tumors in male rats, but the data left the NTP scientists with a "lower level of certainty" that exposure to cell phone radiofrequency radiation caused the tumors. During that time, there have been no shortage of studies looking at the mobile phones and cancer - with evidence both supporting and contradicting a connection between the two - and still more research is ongoing. The decade-long, $25 million federal study confirms reports by EWG from 2009 and 2013 that highlighted potential health risks from cellphones and wireless devices, especially for children. He noted some additional unusual findings in the study, and said his team is continuing to assess them, but emphasized that based on all available scientific information the agency does not believe there are adverse health effects in humans caused by cellphone radiation. "Even with frequent daily use by the vast majority of adults, we have not seen an increase in events like brain tumors", the FDA's statement says. 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".