Hormesis and High-Risk Groups

The concept of hormesis (i.e., biological phenomena characterized by dose–response relationships displaying low-dose stimulation and high-dose inhibition) has important implications for current risk assessment practices because of its generalizability with respect to experimental model, agent, and endpoint measured. This paper addresses the question of whether hormesis is present in high-risk subpopulations and highly susceptible species. Evaluation of published data revealed that hormetic dose–response relationships occur with similar quantitative characteristics among species and individuals that display widely differing susceptibility to various toxicants. This observation suggests that the cause of the differential susceptibility in the more susceptible organisms is not due to the absence of the hormetic response but to some other factor(s). However, despite the recognition that hormetic responses are common and similar in susceptible and resistant organisms there are sufficient examples indicating that some strains/individuals may lack the capacity to produce the low-dose stimulatory response. Thus, the capacity to display hormetic effects is one of a variety of factors affecting differential susceptibility to xenobiotics and needs to be addressed within the hazard assessment process.