Hormesis - Policy Consequences

Policy Consequences

Regulatory agencies such as the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), and the Nuclear Regulatory Commission (NRC) traditionally use a linear no-threshold model for carcinogens (including radiation). In the linear model, the assumption is that there is no dosage that has no risk of causing cancer. While this linear approach remains the default, with sufficient mechanistic evidence suggesting a non-linear dose-response, EPA allows for the derivation of a threshold dose (a.k.a. reference dose) below which it is assumed that there is no risk for cancer.

While proponents of hormesis argue that changing to a hormesis model would likely change exposure standards for these toxicants in air, water, food and soil, making the standards less strict, other scientists point out that low dose stimulation can have extremely adverse effects. For example, research by Retha Newbold at the US National Institute of Environmental Health Sciences has shown that while relatively high doses of a xenobiotic estrogen, diethylstilbestrol, during fetal development cause weight loss in adulthood, extremely low doses cause grotesque obesity. Similarly, low doses of the phthalate DEHP cause increased allergic responses to allergens, while higher doses have no effect. Low dose stimulation can have profoundly adverse consequences. Wider use of the hormesis model would affect how scientists design and conduct studies and the selection of models that estimate risk. In all likelihood, recognizing that low dose effects can't be predicted from high dose experiments would force a strengthening of public health standards, not their weakening, as hormesis proponents would argue.