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Hormesis gets massive data support (homeopathy?)

27th March 2007 by Arrow Durfee Posted in Uncategorized

These poor guys are trying hard. Dose size is everything in homeopathy. I suspect that someday they will sufficiently twist their minds and their explortions in science to figure out how homeoapthy works, but it will be in the quantum physics level………………Arrow

Hormesis gets massive data support (homeopathy?)

2007-3-20 20:15

Hormesis gets massive data support
The new theory could overturn scores of environmental regulations.

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.

Calabrese and colleagues analyzed 2189 dose–response curves generated by a National Cancer Institute investigation that was looking for chemicals that might make good antitumor drugs. The chemicals include many synthetic and natural organic compounds as well as inorganic and organometallic chemicals. Few, if any, industrial compounds appear in the set.

The cancer researchers exposed the 13 different strains of yeast to 5 doses of each of the chemicals. They looked for compounds that blocked growth in mutant yeast cells at high doses because these chemicals might also be able to kill human cancer cells, says Julian Simon, who is a cancer researcher at the Fred Hutchinson Cancer Research Center and who organized the study.

If hormesis were valid, then these chemicals would make the yeasts grow better at low doses, the researchers thought. To test this, Calabrese and colleagues determined the amount that did not affect growth, known as the benchmark dose. If hormesis applied, then doses lower than the benchmark dose would be more likely to enhance growth. If the threshold model held, then these lower doses would have an equal chance of enhancing, inhibiting, or not perturbing growth. When the researchers compared responses below the benchmark dose, they found that growth was enhanced. Indeed, they found that this occurred in most of the responses.

Several toxicologists and statisticians say that Calabrese’s team modified standard procedures for identifying the benchmark dose in their analysis. Some of these scientists add that the modifications were needed to study such low doses, whereas others question the statistical methods used in the new study. “I know that they are trying to find out if this data on aggregate supports hormesis, but there are ways of doing this that have already been evaluated in the literature, and this is not one of them,” says Christopher Portier of the National Institute of Environmental Health Sciences about the mathematical analysis.

Others, including Tony Cox, a biomathematical modeler with research consultants Cox Associates, describe the work as “important, suggestive, and provocative.” The new paper makes an important contribution to this debate, notes Cox, who adds, “I believe everyone would benefit from further analysis of this data set. This would show whether the authors’ conclusions are robust to changes in modeling assumptions.”

Calabrese is more certain. “There is little justification to continue to accept and use the threshold model, and growing evidence to support the hormesis model,” he says. “How often can the threshold model be wrong before it is questioned and set aside? Reasonable people who care about public health or even the concept of truth must ask that question.”

toxsci.oxfordjournals.org/cgi/content/abstract/94/2/368

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