Ionizing Radiation: Dose Tolerability and Hormesis

Hormesis is rarely mentioned in publications on radiation protection. Among environmental factors acting according to the hormesis model are numerous substances and chemical elements, light, ultraviolet and products of water radiolysis. By analogy with other environmental agents, an evolutionary adaptation to natural background radiation can be expected. The experimental evidence in favor of hormesis and adaptive responses to ionizing radiation is considerable, which means that experimental data are partly at variance with epidemiological studies. The main problems with the epidemiological research of low-dose low-rate exposures are potential bias and inter-study heterogeneity i.e. uneven quality of studies analyzed together in reviews and meta-analyses. The overestimation of medical consequences of the Chernobyl accident has been commented previously. Along with the elevated cancer risk, an increased risk of non-neoplastic diseases has been reported, whereas no plausible physiological mechanisms are known. This can be seen as a circumstantial evidence in favor of bias e.g. self-selection: dose-related differences in self-reporting and medical surveillance. Individuals knowing their higher doses or residing in more contaminated areas would be averagely more motivated to visit medical institutions, being at the same time given more attention, the diagnostics thus being more efficient in patients with higher dose estimates. The dose-effect relationships between low-dose low-rate exposures and non-neoplastic diseases call in question such relationships for cancer reported by the same and other scientists. Several examples of questionable reports and conclusions are discussed here along with the motives to overestimate medical consequences of low-dose low-rate exposures to ionizing radiation.

Keywords: dose limits, ionising radiation, radiation protection, carcinogens