Let us try to explain why even some of the best international experts disagree about the effects of radiation at low doses. In addition to the information provided here, the Health Physics Society has published Radiation and Risk: Expert Perspectives on its website, a compilation of papers on topics including natural radiation, medical applications of radiation, effects of natural and man-made radiation on the environment, safety controls of nuclear energy production, risk communication, and the regulatory implications of radiation safety.
As a basis, it is important to realize that a disease caused by radiation will generally not look or act any different than the same disease caused by something else. So if someone has cancer or a child has a birth defect, we can’t simply look at it and determine what caused it. Plus, since approximately 42 in every 100 of us will get cancer in our lifetime, it is very difficult to see an extra cancer that might be caused by radiation exposure. For example, if approximately 42,000 people out of 100,000 people will get cancer in their lifetime, it is very hard to tell if 42,100 cancers is really more than the expected 42,000 cancers or if 41,900 cancers is really less than expected or if both are just a normal variation. Exactly who and how many people in the group of 100,000 will actually get a cancer is unknown. The estimate that 42 of 100 or 42,000 out of 100,000 will get a cancer is based on statistics, like rolling dice. If you roll dice six times and don’t get a four, does that mean the dice are loaded or is that just a statistical variation?
Experts agree that high doses of radiation cause harmful effects. Even as early as the 1950s, when scientific groups were creating radiation protection guidelines, no one really knew what the effects of radiation at low doses were or if there were any. For many reasons, some political, it was decided to assume that the radiation dose and the effect of the dose were linear and proportional—this means for a given dose of radiation to a person, there is some possibility of a radiation effect; if the dose of radiation is doubled, there is twice the possibility and so on. It was also decided that at any dose, no matter how small, there could be an effect (or no threshold). We really had only the knowledge that a lot of radiation was harmful, but we needed to make some assumptions about low doses of radiation so protection standards could be set. Setting radiation protection standards required erring in these assumptions on the safe side, that is, setting a standard lower than it may have to be if the real level of hazard could be known. This was and still is the basis for the Linear No-Threshold Hypothesis (LNT).
Even though LNT was intended for scientists to use in setting radiation protection standards and not for general use, and because it was easy to use and explain, the media and public quickly promoted LNT as fact rather than saying we don’t know the effects of low doses of radiation or that low doses of radiation are safe. So, for several decades, we have simply been assuming that low doses of radiation carry a risk. That still works well when setting radiation protection standards. However, since no activity is risk-free, we really need to ask ourselves what dose of radiation is safe—not risk-free, but safe.
Later in this discussion we are going to share what recent science has found and why it can be difficult to determine what effect a low dose of radiation has on a human body. Keep that in mind as you are reading because you are going to read that sometimes radiation might produce “good” effects and sometimes it might produce “bad” effects—at low doses of radiation, the possibility of an effect depends on many things. That is why it can be confusing. It is also how some people are able to say low-dose radiation is harmful while others can say it isn’t—because they can take the information we are sharing and use it so that it appears to support their case. Before we go into more detail on the scientific aspects of low-dose radiation exposure we want to first discuss two other important influences in this area of disagreement—social and political influences. For now, here’s the bottom line: at low doses of radiation, there is no consistent evidence of an effect in humans. Saying that doesn’t mean nothing occurs, it’s just that, if it does, we simply can’t detect it with current studies.