Human populations have always been exposed to ionizing radiation, and more so in modern life due to its use in medicine, industry and the armed forces. Whilst the risks to human health from medium and high-level radiation are relatively well-understood, the risks at lower levels are less clear. A new study published in the Proceedings of the Royal Society revealed that health risks associated with low-level exposure to ionizing radiation are less pronounced compared to other lifestyle factors such as obesity, smoking and air pollution.

The restatement is intended to better inform policy decisions and show where crucial gaps in knowledge lie. It clarifies the scientific evidence available from a variety of sources, and ranks them as to how much they enjoy consensus support from the scientific community. The study concludes that the overall risk to human health from low-level radiation exposure is small, particularly when compared with general risks from modern society.

"We know a great deal about the health risks from radiation thanks to exceptionally careful studies of groups of people exposed to different levels from nuclear bombs or accidents, medical exposure of patients, naturally occurring sources (such as radon), and workers in the nuclear industry and medicine. From these studies it is clear that moderate and high doses of radiation increase the risk of developing some types of cancer," said professor Angela McLean, lead author and Co-Director at the Oxford Martin Programme on Collective Responsibility for Infectious Disease.

The team illustrate the size of this increase in risk by using the following example. 100 individuals were each briefly exposed to 100 mSv (millisievert is the measure of radiation dose), then, on average over a lifetime, one of them would be expected to develop a radiation-induced cancer, whereas 42 of them would be expected to develop cancer from other causes. To put 100 mSv in context, the low dose from a CT scan of the whole spine is 10 mSv, while the average dose from natural background radiation in the UK is 2.3 mSv each year.

Professor McLean said, "Despite the depth of our knowledge, there are still many unknowns. Even the best designed epidemiological study finds it hard to distinguish between no extra risk and a small additional risk at low levels of exposure and we have to make some important assumptions here, particularly for the purposes of radiation protection. For example, no human study has conclusively shown an increase in hereditary disease in the children of irradiated parents, but radiation protection calculations assume some risk is present because of evidence from large animal experiments."