FRIDAY, May 27, 2016 (HealthDay News) -- Experts at the U.S. National Institutes of Health are questioning the validity of a widely reported study in rats that linked cellphone radiation to tumors.
The study, released Friday by the federal government's National Toxicology Program (NTP), found "low incidences" of two types of tumors in male rats exposed to the type of radio frequencies emitted by cellphones, the Wall Street Journal reported.
The two types of tumors were glioma brain cancer and benign schwannomas of the heart, according to the $25 million study that is one of the largest and most comprehensive to assess the health impacts of cellphones.
"Given the widespread global usage of mobile communications among users of all ages, even a very small increase in the incidence of disease resulting from exposure to [radio-frequency radiation] could have broad implications for public health," according to an NTP summary of partial findings from the study released late Thursday, the WSJ reported.
However, NIH experts were quick to highlight flaws in the study, according to the Associated Press.
For example, they pointed out that the study exposed rats to very high levels of cellphone radiation, beginning in the womb and then through the first two years of the rats' life. Even then, only 2 percent to 3 percent of male rats -- and no females -- developed a tumor.
The fact that none of the female rats developed a tumor is odd, the NIH experts said, as is the fact that rats who did not get exposed to the radiation died at higher rates than those who did get exposed.
The unexposed rats also failed to develop tumors at a rate that would be expected in a "normal" population, the NIH experts noted.
Based on these findings, "I am unable to accept the authors' conclusions," wrote outside reviewer Dr. Michael Lauer, deputy director of NIH's office of extramural research. "I suspect that this experiment is substantially underpowered and that the few positive results found reflect false positive findings."
He also said that the fact rats exposed to the radiation actually lived longer "leaves me even more skeptical of the authors' claims."
The complete results of the NTP study will be released by the fall of 2017, the NTP said.
The NIH helped oversee the study, and earlier this week said, "It is important to note that previous human, observational data collected in earlier, large-scale population-based studies have found limited evidence of an increased risk for developing cancer from cellphone use."
Many studies have found no link between cellphones and harmful health effects. For example, a recently released Australian study found no increase in brain cancer rates since mobile phones became available there nearly three decades ago, and similar findings have been made in other countries.
Others believe the new findings may have merit, however. Ron Melnick ran the NTP project until retiring in 2009. He recently reviewed the study and said: "Where people were saying there's no risk, I think this ends that kind of statement."
In the meantime, the study's impact on Federal Communications Commission (FCC) cellphone safety rules is unclear.
"Scientific evidence always informs FCC rules on this matter," said a spokesman for the agency, which has been briefed on the findings. "We will continue to follow all recommendations from federal health and safety experts including whether the FCC should modify its current policies."
Visit the U.S. National Cancer Institute for more on cellphones and cancer risk.