Data from the largest-ever animal study of cell phone radiation effects, released last week by the federal National Toxicology Program (NTP), found an association between cell phone radiation and an increased risk for cancer.
NTP senior scientist John Bucher, PhD, emphasized that the animals (rats and mice) in the study were exposed to a high dosage of cell phone radiation.
"The levels and duration of exposure to RFR [radiofrequency radiation] were much greater than what people experience with even the highest level of cell phone use, and exposed the rodents' whole bodies," Dr Bucher said in a statement. "So, these findings should not be directly extrapolated to human cell phone usage.
"We note, however, that the tumors we saw in these studies are similar to tumors previously reported in some studies of frequent cell phone users," he added.
The study showed that after 2 years, high exposure to RFR appeared to affect male rats but not female rats or mice, according to draft results from the two studies that were conducted.
Specifically, exposure to Global System for Mobile Communications (GSM)–modulated or to Code Division Multiple Access (CDMA)–modulated cell phone RFR was associated with an increase in the incidence of malignant schwannoma in the heart of male rats.
There was also a significant increase in incidence of right ventricular cardiomyopathy in both male and female rats exposed to 3 watts per kilogram (W/kg) and 6 W/kg of GSM-modulated RFR, and in male rates exposed to 6 W/kg of CDMA-modulated RFR.
The researchers also observed other, albeit weaker, effects for both modulations that included malignant glioma in the brain, adenomas in the pituitary gland (pars distalis), and pheochromocytomas of the adrenal medulla.
In addition, marginal effects were seen for GSM-exposed male rats in the prostate gland and in pancreatic islets, and granular cell tumors of the brain were observed. Such effects were not observed in CDMA-exposed rats. Conversely, liver effects were noted only in CDMA-exposed male rats, although the relationship between these responses and exposure to GSM or CDMA RFR remains unclear.
The US Food and Drug Administration (FDA), which is responsible jointly with the Federal Communications Commission for regulating wireless communication devices, reacted to the new findings with a statement. In it, Jeffrey Shuren, MD, JD, director of the FDA's Center for Devices and Radiological Health, cautioned that "looking at the results in animals, the conclusions still require careful discussion, as our preliminary understanding of the NTP results is that the study found mostly equivocal, or ambiguous, evidence that whole-body radiofrequency energy exposures given to rats or mice in the study actually caused cancer in these animals.
"There are additional unusual findings from the study, such as the exposed rats living longer than the control group rats, that we are assessing to understand how that may be relevant to the results," Dr Shuren added.
The NTP study was proposed by the FDA in 1999. At that time, few epidemiologic and long-term experimental studies of the effects of radiofrequency energy exposure from cell phones had been conducted.
In the 20 years since then, a myriad of scientific studies have been published regarding an association between RFR and cancer risk. The results have been contradictory and have evoked strong reactions on both sides of the issue.
In 2011, the World Health Organization's International Agency for Research on Cancer declared the kind of radiation emitted by cell phones to be a "possible carcinogen" on the basis of human epidemiologic studies that found increased gliomas and acoustic neuromas in long-term cell phone users, which further stirred the flames of the controversy.
In this latest study, the NTP examined the effects of high exposure to radiofrequency energy in rodents. Interim findings from the project were released in May 2016. They showed an increase in malignant gliomas in the brain and schwannomas of the heart. The mature results that have just been released reflect the earlier findings, but these are still considered to have draft status, and the NTP will hold an external expert review of its complete findings from these rodent studies March 26-28.
Malignant and Nonmalignant Changes
The NTP conducted two studies, one with rats and one with mice.
In the rat study, male and female Hsd:Sprague Dawley SD rats were exposed to time-averaged whole-body specific absorption rates of GSM- or CDMA-modulated cell phone RFR at frequencies of 900 MHz administered at 1.5, 3, or 6 W/kg. The rats received RFR while in utero, during lactation, and after weaning for 28 days or 2 years.
To put the exposure levels in context, the lowest power level for the rats was equal to the highest level that is currently permitted for local tissue exposures to cell phone emissions. The rodents were exposed for about 9 hours a day in increments of 10 minutes on, 10 minutes off. The studies used 2G and 3G frequencies and modulations that are currently used in voice calls and texting in the United States.
At the 14-week interim evaluation, there was an increase in the incidence of right ventricular cardiomyopathy in the heart of male rats following exposure to GSM- and CDMA-modulated cell phone RFR as compared with controls.
No changes in sperm motility and sperm counts were observed in male rats exposed to GSM- or CDMA-modulated cell phone RFR. Exposure to whole-body GSM- or CDMA-modulated RFR for up to 6 W/kg did not significantly alter reproductive organ histopathologic or sperm parameters.
In the brain, malignant glioma was observed across all groups of GSM male rats exposed to 6 W/kg CDMA and in CDMA female rates exposed to 1.5 W/kg in comparison with controls, but these findings did not reach statistical significance. There were also occurrences of glial cell hyperplasia in the brain of GSM and CDMA male rats and CDMA female rats; none were observed in the controls.
In the pituitary gland of male rats, there was an increase in the incidence of adenoma in all GSM-exposed groups, but this did not reach statistical significance. There was a significant increase in the incidence of adenoma in CDMA male rats exposed to 3 W/kg in comparison with controls.
A significant increase in the incidence of benign, malignant, or complex pheochromocytoma (combined) was also observed in the adrenal medulla of GSM male rats exposed to 1.5 and 3 W/kg and in CDMA female rats exposed to 1.5 W/kg. In GSM female rats exposed to 6 W/kg, there was an increase in incidence of hyperplasia in the adrenal medulla.
The researchers also studied a range of other noncancer health effects in rats and mice, including changes in body weight, evidence of tissue damage from RFR-generated heat, and genetic damage. Although body weight was lower in exposed newborn rats, they grew to normal size.
One curious finding was that after 2 years, survival rates for male rats that were exposed to RFR were higher compared to the controls. Only 28% of male rats in the control arm survived to the end of the study, compared to 48% to 68% in the exposure arms.
"These studies were complex and technically challenging, but they provide the most comprehensive assessment, to date, of health effects in rats and mice from exposure to RFR," said Dr Bucher. "Cell phone technologies are constantly changing, and these findings provide valuable information to help guide future studies of cell phone safety."
Weighing In on the Data
Paolo Boffetta, MD, a professor of environmental medicine, public health, hematology, and medical oncology at the Icahn School of Medicine at Mount Sinai, New York City, noted that these findings support the hypothesis that the radiation emitted from cell phones poses some risk.
However, he emphasized that results from animal studies often do not extrapolate to humans. "Rodents are not comparable to humans," Dr Boffetta told Medscape Medical News. "In this case, the dosage was higher then what we'd normally see, and the animals are also in a stressful situation."
He noted that it is unclear why the male rats were affected and not the female rats. In addition, the tumor that developed in the heart of the rats is quite rare, so that effect is also not clear.
Many of the human cell phone studies have been quite large, and heart tumors have not been observed. "Even if there were just a handful, they would have stood out, given how rare they are," he said. "It was not a finding one would expect."
But even with limitations, the new findings do show that some damage can occur with high exposure. "More research needs to be done in humans, although that will be difficult, given the fact that probably 90% of people have a cell phone," Dr Boffetta said. "It's not like trying to do a study on smoking, where only some do smoke and others don't."
Another expert also weighed in on the findings.
"The NTP study is the second US government–sponsored animal study that demonstrates increased cancer risk from exposure to low intensity, nonthermal levels of microwave radiation," said Joel Moskowitz, PhD, director, Center for Family and Community Health, School of Public Health, University of California, Berkeley.
A previous study was conducted years ago by the US Air Force. It found a similar pattern of low incidence of multiple types of tumors in male rats exposed to microwave radiation. "When the tumor findings were combined by the Air Force researchers, the rats exposed to microwave radiation were three times more likely to get cancer than the control rats," Dr Moskowitz said. "The microwave radiation exposure in the Air Force study was much lower in intensity than the radiation in the NTP studies."
Dr Moskowitz noted that these draft reports have identified elevated risk for several types of tumors in rats and mice exposed to cell phone radiation.
"Our current federal guidelines for radiofrequency radiation, which were adopted in 1996, were designed only to protect us from thermal levels of exposure," he said. "The federal RFR limits should be reassessed and strengthened in light of these findings."
Dr Boffetta has disclosed no relevant financial relationships.
National Institutes of Health. NTP technical report 595. Full text
Medscape Medical News © 2018
Cite this: Largest Animal Study of Cell Phone Radiation and Cancer Risk - Medscape - Feb 06, 2018.