Clouding the debate about radiation risks are the multiple causes of cancer, including diet, smoking and other habits. That's why it is extremely difficult to prove any direct link between an individual's cancer and radiation, or pinpoint where one cause begins and another ends.
The ICRP recommends keeping radiation exposure down to 1 millisievert per year and up to 20 millisieverts in a short-term emergency, a standard that takes into account the lessons of Chernobyl.
"Health risks from annual radiation exposure of 20 millisieverts, the current level for issuance of orders to evacuate an affected area, are quite small particularly when compared against the risks from other carcinogenic factors," the ICRP says.
The risk of getting cancer at 20 millisieverts raises the already existing 25 percent chance by an estimated 0.1 percent, according to French ICRP member Jacques Lochard, who visits Japan often to consult on Fukushima.
While that's low, he says it's not zero, so his view is that you should do all you can to reduce exposure.
Kazuo Sakai, a Japanese ICRP member, said he was interested in debunking that generally accepted view. Known as the "linear no threshold" model of radiation risk, the ICRP-backed position considers radiation harmful even at low doses with no threshold below which exposure is safe.
Sakai called that model a mere "tool," and possibly not scientifically sound.
He said his studies on salamanders and other animal life since the Fukushima disaster have shown no ill effects, including genetic damage, and so humans, exposed to far lower levels of radiation, are safe.
"No serious health effects are expected for regular people," he said.
The parliamentary investigation found that utilities have repeatedly tried to push Japanese ICRP members toward a lenient standard on radiation from as far back as 2007.
Internal records at the Federation of Electric Power Companies obtained by the investigative committee showed officials rejoicing over how their views were getting reflected in ICRP Japan statements.
Even earlier, Sakai received utility money for his research into low-dose radiation during a 1999-2006 tenure at the Central Research Institute of Electric Power Industry, an organization funded by the utilities.
But he said that before his hiring he anticipated pressures to come up with research favorable to the nuclear industry and he made it clear his science would not be improperly influenced.
Niwa, a professor at Fukushima Medical University, said that residents need to stay in Fukushima if at all possible, partly because they would face discrimination in marriage elsewhere in Japan from what he said were unfounded fears about radiation and genetic defects.
Setting off such fears are medical checks on the thyroids of Fukushima children that found some nodules or growths that are not cancerous but not normal.
No one knows for sure what this means, but Yoshiharu Yonekura, president of the National Institute of Radiological Sciences and an ICRP member, brushes off the worries and says such abnormalities are common.
The risk is such a non-concern in his mind that he says with a smile: "Low-dose radiation may be even good for you."
Associated Press researcher Julie Reed contributed to this report. Follow Yuri Kageyama on Twitter at www.twitter.com/yurikageyama