Defining hormesis

Abstract

<jats:p> Much confusion surrounds the concept of hormesis and what its biological meaning represents. This paper provides a definition of hormesis that addresses its historical foundations, quantitative features, and under-lying evolutionary and toxicologically based mechanistic strategies. Hormesis should be considered an adaptive response characterized by biphasic dose responses of generally similar quantitative features with respect to amplitude and range of the stimulatory response that are either directly induced or the result of compensatory biological processes following an initial disruption in homeostasis. Given the limited magnitude of the stimulatory response (i.e., usually 30–60% greater than controls at maximum), heightened study design and replication requirements are often necessary to ensure reliable judgments on causality. Even though hormesis is considered an adaptive response, the issue of beneficial/harmful effects should not be part of the definition of hormesis, but reserved to a subsequent evaluation of the biological and ecological context of the response. </jats:p>

Hormesis and stage specific toxicity induced by cadmium in an insect model, the queen blowfly, Phormia regina Meig.

“…usually 30-60% greater than controls at maximum), a stringent study design and replication requirement is necessary to ensure reliable judgments on causality (Calabrese and Baldwin, 2002). These experiments were replicated seven times to assess whether the low-dose stimulatory response was due to random variation, and not necessarily an example of hormesis.…”

“…Hormesis, a dose-response phenomenon characterized as a low dose stimulation, high dose inhibition, is an adaptive dose-response relationship that occurs as the result of a compensatory mechanism following a disruption in homeostasis (Calabrese and Baldwin, 2002). The phenomenon of hormesis is widely reported in the scientific literature and is broadly generalizable according to chemical class, biological model, and endpoint ( Calabrese and Baldwin, 1997a).…”

Intermittent calorie restriction largely counteracts the adverse health effects of a moderate‐fat diet in aging C57BL/6J mice

“…Moreover, an intermittent CR regimen is more feasible to maintain. Importantly, increasing evidence points out that the beneficial health effects of (intermittent) CR are not solely caused by reduced body weight 24, 25. Timing and limitation of meal frequency affect the circadian rhythm and might induce a repetitive challenge that most likely will contribute to the health promoting effects 26, 27, 28, 29.…”

Nutritional hormesis

“…The hormetic dose-responses satisfied rigorous a prior evaluative criteria (including to varying degrees: strength of study design, magnitude of stimulation, statistical significance and reproducibility of findings). With stimulation used in the context of Calabrese and Baldwin's (2002) definition, that is, a response opposite to that observed at higher (i.e., greater than threshold) doses, the maximum stimulatory responses were typically only approximately 30-60% greater than the concurrent control, with nearly 80% of the maximum responses being less than twice the control value. In general, the widths of the stimulatory responses were also modest, typically extending over a dose range of 20-fold (i.e., 1/20) or less immediately below the NOAEL (No Observed Adverse Effect Level -the highest dose not differing in a statistically significant manner from the control group, which serves as a toxicological quasi-threshold), and often less than 10-fold (i.e., 1/10).…”