Population Studies and Molecular Mechanisms of Human Radioadaptive Capabilities: Is It Time to Rethink Radiation Safety Standards?

Abstract

The evolution of man on Earth took place under conditions of constant exposure to background ionizing radiation (IR). From this point of view, it would be reasonable to hypothesize the existence of adaptive mechanisms that enable the human organism to safely interact with IR at levels approximating long-term natural background levels. In some situations, the successful operation of molecular mechanisms of protection against IR is observed at values significantly exceeding the natural background level, for example, in cancer cells. In 15-25% of cancer patients, cancer cells develop a phenotype that is resistant to high doses of IR. While further investigations are warranted, the current evidence suggests a strong probability of observing positive health effects, including an increased lifespan, a reduced cancer risk, and a decreased incidence of congenital pathologies, precisely at low doses of ionizing radiation. This review offers arguments primarily based on a phenomenological approach and critically reconsidering existing methodologies for assessing the biological risks of IR to human health. Currently, in the most economically developed countries, there are radiation safety rules that interpret low-dose radiation as a clearly negative environmental factor. Nowadays, this approach may pose significant challenges to the advancement of radiomedicine and introduce complexities in the regulation of IR sources. The review also examines molecular mechanisms that may play a key role in the formation of the positive effects of low-dose IR on human radioadaptive capabilities.

Keywords: carcinogenesis; hormesis; ionizing radiation; low-dose radiation; radiation safety; radioadaptive response; radioresistance.

Figure 1

Graphical representation of the main hypotheses used to explain the biological effects of low-dose ionizing radiation. (a) Presented is a graphical diagram illustrating the linear increase in human health risks at any level of ionizing radiation (LNT hypothesis). (b) An illustration of the ionizing radiation threshold hypothesis, which states that negative effects on human health occur only above a certain dose rate and are then subject to linear dependence. (c) An illustration of the theory of radiation hormesis, according to which irradiation at dose loads close to the natural background has positive effects on human health. (d) The multiphase theory of hormesis explains the large scatter of data on biological effects observed by researchers when using similar dose loads, and also the observation of approximately the same biological effects at significantly different dose loads.