Rasmusen Weblog

So I googled "hormesis", mainly for future reference. "An Introduction to Radiation Hormesis", by S. M. Javad Mortazavi is poorly written but has good content:

It is a general belief that low doses of ionizing radiation produce detrimental effects proportional to the effects produced by high-level radiation. Over the past decades, however, some pioneer scientists reported that low-dose ionizing radiation is not only a harmless agent but often has a beneficial or hormetic effect. That is, low-level ionizing radiation may be an essential trace energy for life, analogous to essential trace elements. It has been even suggested that about one third of all cancer deaths are preventable by increasing our low dose radiation.

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In the early 1940s C. Southam and his coworker J. Erlish found that despite the fact that high concentrations of Oak bark extract inhibited fungi growth, low doses of this agent stimulated fungi growth. They modified Starling's word "hormone to "hormesis" to describe stimulation induced by low doses of agents which are harmful or even lethal at high doses. They published their findings regarding the new term "hormesis" in 1943 (Bruce M. 1987).

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In 1927 Herman J. Muller,a Nobel Prize winner, found that X-rays are mutagen and there is a linear relationship between mutation rate and dose.
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According to UNSCEAR report (1994), among A-bomb survivors from Hiroshima and Nagasaki who received doses lower than 200 mSv, there was no increase in the number of total cancer death. Mortality caused by leukemia was even lower in this population at doses below 100 mSv than age-matched control cohorts.

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Although still we do not know the entire mechanisms of radiation hormesis, the following theories may explain this process:

1- D...NA repair (Mollecular level)
According to this theory, low doses of ionizing radiation induce the production of special proteins, that are involved in DNA repair processes (Ikushima 1996). ...

2- Free radical detoxification (Molecular level)
In 1987 Feinendengen and his co-workers indicated that low doses of ionizing radiation cause a temporary inhibition in DNA synthesis (the maximum inhibitionat 5 hours after irradiation). This temporary inhibition of DNA synthesis would provide a longer time for irradiated cells to recover (Feinendengen et al. 1987). This inhibition also may induce the production of free radical scavengers, so irradiated cells would be more resistant to any further exposures.

3- Stimulation of immune system (Cellular level)
Despite the fact that high doses of ionizing radiation are immunosupressive, many studies have indicated that low doses radiation may stimulate the function of the immune system. In 1909 Russ first showed that mice treated with low-level radiation were more resistant against bacterial disease (Russ VK 1909).

Another article is "Nietzsche's Toxicology: Whatever doesn't kill you might make you stronger" (Scientific American, 2003)

This idea may sound bizarre, but such adaptation to stress is common, says physiologist Suresh Rattan of �rhus University in Denmark. Exercise, for instance, plays biochemical havoc with the body : starving some cells of oxygen and glucose, flooding others with oxidants, and depressing immune functions. "At first glance, there is nothing good for the body about exercise," he notes.

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The definitive rat study that linked high doses of dioxin to cancer, published in 1978 by Richard Kociba of Dow Chemical and his colleagues, also found that low doses reduced the incidence of tumors.

Finally, see "Radiation Hormesis"