The response of living organisms to a low-radiation environment and its implications for radiation protection

Life has evolved on Earth for about 4 billion years in the presence of the natural background of ionizing radiation. Today the natural background radiation is extremely small, however it may be significant enough for living organisms to respond to it. A better understanding of this response is relevant not only for improving our knowledge on life evolution, but also for assessing the robustness of the present radiation protection system at low doses. Given the large uncertainties in epidemiological data below 100 mSv, quantitative evaluation of these health risk is currently obtained with the aid of radiobiological models. These predict a health detriment, caused by radiation-induced genetic mutations. This article focuses on the role that epigenetic mechanisms can have in the responses to low dose and protracted exposures, particularly to natural background radiation. Many lines of evidence show that epigenetic modifications are involved in non-linear responses relevant to low doses and that genetic and epigenetic effects share, in part, a common origin. Cell response to low doses of ionizing radiation appears more complex than that assumed for radiation protection purposes. Studying the changes occurring in various living organisms at reduced radiation background have opened a new avenue to answer whether low doses are detrimental or beneficial. (author)