Scientists at the National Toxicology Program, which carried out the major study, this week published final reports that express more confidence in links between cellphone radiation exposure and some tumors in rats than they did in draft reports earlier this year.
Their final reports, for example, concluded that there is “clear evidence” that male rats exposed to high levels of cellphone radiation developed cancerous heart tumors, after initially saying there was just “some evidence”—a less certain classification.
They also said there was “some evidence” of brain and adrenal gland tumors in male rats that were exposed to cellphone radiation after characterizing that evidence as “equivocal” earlier this year.
The changes were made after scientists in charge of the study accepted the recommendations of a panel of experts that reviewed the findings.
In female rats and male and female mice, the link between cancers and exposure to cellphone radiation was less clear, the researchers said. One surprising finding in the study was that exposed male rats lived longer and had a significant reduction in a type of kidney disease.
John Bucher, a senior scientist at the NTP, warned on a call that the exposure used on rodents in the study was “not directly comparable to the exposures that humans typically experience when using a cellphone.”
The study focused on radio frequency radiation akin to what’s used in 2G and 3G cellphones and exposed animals to cellphone radiation at levels higher than what human cellphone users typically experience.
Mr. Bucher said he personally has “no hesitation at all” in picking up the phone for short calls, but for longer calls he tends to use “earbuds or some other way of increasing the distance between the cellphone and my body.”
He said the NTP’s role was to conduct the research for regulatory agencies and the public, not to issue warnings to consumers.
The U.S. Food and Drug Administration asked the NTP to carry out the study in 1999 because usage of cellphones was widespread and little was known about the impact of cellphone radiation.
Mr. Bucher said future research will focus on newer generations of wireless technology such as 4G, 5G and Wi-Fi and that researchers had learned ways to accelerate the speed of new studies.