Hormesis, an update of the present position

Abstract

The ongoing debate over the possible beneficial effects of ionising radiation on health, hormesis, is reviewed from different perspectives. Radiation hormesis has not been strictly defined in the scientific literature. It can be understood as a decrease in the risk of cancer due to low-dose irradiation, but other positive health effects may also be encompassed by the concept. The overwhelming majority of the currently available epidemiological data on populations exposed to ionising radiation support the assumption that there is a linear non-threshold dose-response relationship. However, epidemiological data fail to demonstrate detrimental effects of ionising radiation at absorbed doses smaller than 100-200 mSv. Risk estimates for these levels are therefore based on extrapolations from higher doses. Arguments for hormesis are derived only from a number of epidemiological studies, but also from studies in radiation biology. Radiobiological evidence for hormesis is based on radio-adaptive response; this has been convincingly demonstrated in vitro, but some questions remain as to how it affects humans. Furthermore, there is an ecologically based argument for hormesis in that, given the evolutionary prerequisite of best fitness, it follows that humans are best adapted to background levels of ionising radiation and other carcinogenic agents in our environment. A few animal studies have also addressed the hormesis theory, some of which have supported it while others have not. To complete the picture, the results of new radiobiological research indicate the need for a paradigm shift concerning the mechanisms of cancer induction. Such research is a step towards a better understanding of how ionising radiation affects the living cell and the organism, and thus towards a more reliable judgement on how to interpret the present radiobiological evidence for hormesis.

The Benefits of Calorie Restriction and Calorie Restriction Mimetics as Related to the Eye

“…This response is similar to the expected hormetic response [8]. According to the theory of "hormesis," toxins and pollutants generally show biphasic dose response, where a low dose of toxin triggers a positive, adaptive stress response, which may help an organism sustain much higher levels of toxins which otherwise cause harmful effects [7][8][9][10][11][12].…”

“…These phytochemicals are referred to as CR mimetics (CRMs) [14,15]. CRMs at low *Address correspondence to this author at the Department of Neurology, Oregon Health and Science University, Portland, OR 97239-3098, USA; Tel: 503-494-5023; E-mail: anekondt@ohsu.edu doses function like toxicants and trigger the adaptive response in the organism [8][9][10]12]. Fruits, nuts, vegetables and herbs together offer an estimated 4000 different kinds of flavonoids [16][17][18] that may have been evolved to fight diseases and insect attack [14], but at proper dosage levels may be extremely beneficial to human health.…”

Biological Effectiveness of Ionizing Radiation: Acute vs. Protracted Exposures

“…This concept does not take into account that DNA damage and repair are permanent processes in dynamic equilibrium. Given the evolutionary prerequisite of best fitness, it would be reasonable to assume that living organisms have been adapted by the natural selection to background levels of ionizing radiation [10]. Accordingly, there must be an optimal exposure level, as it is for many environmental factors: visible and ultraviolet light, different chemical elements and compounds [11], as well as the products from radiolysis of water [12].…”

Food contamination after the Chernobyl accident: dose assessments and health effects

“…protective or beneficial action of low-radiation doses (Johansson, 2003;Vaiserman, 2010;Jaworowski, 2010a), should be taken into account evaluating the exposures from contaminated foodstuffs. Discussing the exclusion of hormesis from the current risk assessment and elaboration of radiation safety standards, Zbigniew Jaworowski (2010a) noted 'It seems to me that the driving force was (and still is) the vested interests of the radiation protection establishment and of the antinuclear power lobby, both concerned that demonstration of the beneficial effects of small radiation doses, and thus of the existence of a threshold for harmful effects occurring near this dose region, will destroy their raison d'etre'.…”