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treepig Donating Member (1000+ posts) Send PM | Profile | Ignore Fri May-21-04 06:23 AM
Response to Reply #5
6. radiation hormesis - ugh...
my oh my, what is to be done when science conflicts with one's prejudices and preconceived notions?

from Science, Vol 302, Issue 5644, 378 , 17 October 2003

HORMESIS: A Healthful Dab of Radiation?

Jocelyn Kaiser
The notion that certain toxic chemicals can be healthful in small doses is stirring new controversy (see main text), but a similar debate about low-dose ionizing radiation has been raging for decades. Now, research that could shed light on possible "radiation hormesis," much of it funded by the U.S. Department of Energy (DOE), is well under way. Although these studies may not soon alter regulators' assumption that any dose of radiation is harmful, the findings about low-dose effects may be provocative.

Radiation risks are now calculated based mainly on cancers among 86,600 survivors of the two atomic bombs dropped on Japan. These human data "are the gold standard," notes carcinogenesis expert Julian Preston of the U.S. Environmental Protection Agency (EPA). The incidence of solid cancers in the survivors rises in a straight line with dose. This suggests that any increase in dose delivers an increase in risk, with no safe level of radiation. But at the lowest doses, there are too few cancers to calculate the actual risks. "The numbers are just not there," says radiobiologist Eric Hall of Columbia University in New York City. To be cautious, public health agencies extrapolate risk in a straight line from higher to lower doses. That leaves open the possibility that something unexpected is going on below the threshold of measured effects.

In this zone, there are hints that a little radiation could even be beneficial. The Japanese bomb survivors who received the lowest doses are living longer than controls, for example. Some studies have found a slightly lower incidence of cancer in people living in places such as western China and Colorado, where natural background radiation levels are three to four times higher than the global average of 2.4 millisieverts per year. And studies dating back to the 1950s report that rodents live about 10% to 20% longer if exposed to small amounts of radiation, notes cancer researcher Arthur Upton of the University of Medicine and Dentistry of New Jersey.

from Crit Rev Toxicol. 2003;33(3-4):443-9.

Metabolic efficiency in response to environmental agents predicts hormesis and invalidates the linear no-threshold premise: ionizing radiation as a case study.

Parsons PA.

La Trobe University, Bundoora, Australia.

Hormesis derives from high metabolic efficiency and hence high fitness that evolve in response to single and multiple environmental agents in low to moderate stress habitats. Consequently, nonlinear fitness continua are an evolutionary expectation for all environmental agents, which invalidates the LNT premise. For ionizing radiation, hormesis is interpreted to be adaptation to background radiation exposures, combined with adaptation to higher radiation exposures dependent on metabolic protection from the array of other abiotic stresses in the environment. This model of radiation hormesis renders suggestions of therapeutic radiation supplementation redundant because of similar health effects from other environmental agents. Furthermore, the model is compatible with a return of exposure levels for radiation protection to higher doses than are presently permissible, a deduction with substantial economic benefits.

but how could radiation be beneficial . . . ?
. . . perhaps by stimulating the immune system . . .

from Crit Rev Toxicol. 2003;33(3-4):431-41.

On radiation hormesis expressed in the immune system.

Liu SZ.

Radiation hormesis is reviewed with emphasis on its expression in the immune system. The shape of the dose-response relationship of the immune functions depends on a number of factors, chiefly the target cell under study, experimental design with emphasis on the dose range, dose spacing, dose rate and temporal changes, as well as the animal strain. For mouse and human T lymphocyte functions in the dose range of 0.01 to 10 Gy a J or inverted J-shaped curve is usually observed. For the more radioresistant macrophages, stimulation of many of their functions is often observed in the dose range up to a few grays. The cellular and molecular mechanisms of the enhancement of immunity induced by low-dose radiation were analyzed on the basis of literature published in the last decade of the past century. Intercellular reactions among the APCs and lymphocytes via distinct changes in expression of relevant surface molecules and secretion of regulatory cytokines in response to different doses of radiation were described. The major signal transduction pathways activated in response to these intercellular reactions were illustrated. The suppressive effect of low-dose radiation on cancer induction, growth, and metastasis and its immunologic mechanisms were analyzed. The present status of research in this field gives strong support to radiation hormesis in immunity with low-dose radiation as one of the mechanisms of cancer surveillance. Further research with new techniques using microarray with biochips to fully elucidate the molecular mechanisms is suggested.

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