Hormesis gets massive support

The new theory could overturn scores of environmental regulations

By Rebecca Renner

Science News—October 4, 2006

Humble yeast cells may be shedding new light on the controversial theory of hormesis. Cancer researchers collected data on 13 strains of yeast, generating a large database of their responses to different chemicals. For low doses, those reactions are best explained by hormesis—a nonintuitive dose–response theory—and not by theories currently used in risk assessment, according to a new analysis by University of Massachusetts toxicologist Edward Calabrese and colleagues, published in Toxicological Sciences online on September 1.

Hormesis (160KB PDF) explains that low doses can have the opposite effect of high doses, such that chemicals that can have harmful biological effects in relatively large amounts can have beneficial effects in small quantities. Calabrese and colleagues have found in scores of recent papers signs that such behavior may be ubiquitous. But risk assessments and environmental regulations throughout the world operate on one of two assumptions: either doses below a toxicological threshold have no adverse effects, or all doses have similar effects.

This means that hormesis has the potential to overturn some environmental regulations, and its relevance to such policies has engendered lively debate. “The proper understanding and utilization of hormesis will do a much better job of both protecting and promoting public health than the policy-based defaults that are currently in use,” Ralph Cook, a physician with RRC Consulting, and Calabrese wrote this summer. Not so, argued Kristina Thayer, a toxicologist with the National Institute of Environmental Health Sciences, and colleagues last year. “If hormesis were used in the decision-making process to allow higher exposures to toxic and carcinogenic agents, this would substantially increase health risks for many, if not most, segments of the general population,” they wrote.

The new analysis is the first to use a single large database to put hormesis to the test against the threshold model, says Calabrese. “In this single, detailed data set, we again find that the threshold model fails to predict the low-dose responses and the hormesis model does,” he says. Read the entire article…