However, the two 10-year, $25 million studies - the most comprehensive assessments of health effects and exposure to radiofrequency radiation in rats and mice to date - do raise new questions about exposure to the ubiquitous devices.
Male rats exposed to very high levels of the kind of radiation emitted by cellphones developed tumours in the tissues around their hearts, according to a draft report by USA government researchers on the potential health risks of the devices.
For humans, who text, watch videos and talk on cell phones, there has always been a concern whether radiofrequency radiation from cell phones might lead to brain tumors. "We studied the maximum that one could achieve during a call in a poorer-connection situation". Some groups were exposed up to 18.5 hours per day for two years. This is a situation, obviously, that people are not going to be encountering in utilizing cell phones.
"Evidence of DNA damage was seen in some tissues of some animals, but we don't feel we have evidence to comment on the biological significance", Bucher said. But don't read too much into that, experts say - because those radiation exposures were much bigger than even the heaviest cellphone users would experience. Female rats exposed to the radiation didn't, and neither male nor female mice showed obvious health problems in a second study.
Bucher and colleagues suggested that the evidence for malignant schwannomas met the risk classification standard of "some evidence of carcinogenic activity".More news: Rams DT Donald named Defensive Player of the Year
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"The reports don't go much further than what we had reported earlier, and I have not changed the way I use a cellphone", NTP senior scientist John Bucher said in a briefing. "We note, however, that the tumours we saw in these studies are similar to tumours previously reported in some studies of frequent cell phone users". "The evidence for an association between cell phones and cancer is weak".
The findings add to years of research meant to help settle the debate over whether cellphone radiation is harmful. "In the meantime, I want to underscore that based on our ongoing evaluation of this issue and taking into account all available scientific evidence we have received, we have not found sufficient evidence that there are adverse health effects in humans caused by exposures at or under the current radiofrequency energy exposure limits". "We believe the current safety limits for cellphones are acceptable for protecting the public health". Animals were assigned to control groups or to groups exposed to various levels of radiofrequency radiation.
A rat that is 2 years old is roughly equivalent to a person living to 70 years old. "It's important to understand that â€" as is commonly done in these types of risk assessment studies â€" the study was created to test levels of radiofrequency energy exposures considerably above the current safety limits for cell phones to help contribute to what we already understand about the effects of radiofrequency energy on animal tissue.
Female rats and mice exposed in the same way did not develop tumours, according to the preliminary report from the US National Toxicology Program (NTP), a part of the National Institute of Environmental Health Sciences.