Radiation hormesis

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Radiation hormesis is a hypothetical model describing the biological response to ionizing radiation, opposed to the conventional linear no-threshold model. It predicts that low doses of radiation below a certain threshold will have some health benefits, usually related to warding off cancer. The proposed biological mechanism involves the slight damage done by the radiation activating DNA repair processes, which will protect against future damage. A report issued by the French Academy of Sciences offered support for the hypothesis. Much of the supportive research is limited to animals for obvious reasons.

The effects of low-level radiation are difficult to quantify because the effect sizes are small and it's difficult to separate the signal from the noise. Both the National Research Council and the United Nations Scientific Committee on the Effects of Atomic Radiation have found that there is insufficient evidence for radiation hormesis to supplant the linear no-threshold model, while noting that a strictly linear dose response should not be expected in all circumstances.

Physics

The radiation damage comes in discrete events, and at the cellular level, the doses of radiation in vicinity of background correspond not to slight damage to DNA, but to low probability of stronger damage that does not vary with dose (the single-track damage is especially strong for alpha particles). Furthermore, the vast majority of damage comes from intracellular sources, not radiation. In light of this, the biological mechanism as outlined above can not apply to the doses in the vicinity of the background.

Hormesis hypothesis proponents tend to propose multiple biological mechanisms having nothing in common other than the final conclusion that "radiation is good for you in low doses", involving a variety of systems, including the immune system — the latter approach to justification of the hormesis tries to escape the physical implausibility of the hormesis effect at near-background levels by changing the proposed mechanism to involve the immune system. This makes the hypothesis far harder to falsify than the original DNA repair version.

Analysis of research

As such, genuine scientific research into the cellular defense responses to radiation appears unlikely to give undue focus to the proposition that the response must be sufficiently strong to result in net benefit at low doses. There is no particular rationale for a researcher to make a prediction that the combined benefit would be larger than the detrimental effects of radiation, rather than, say, half as large. Furthermore, there is no particular rationale to the belief that the window where the net effect is beneficial is wide, and there is no particular rationale to extend the effect to all types of radiation (and especially the alpha particles and nuclei recoil). It appears that the expectation of a beneficial effect of radiation is not arrived at via normal process of scientific inquiry (starting from the biological mechanism and progressing to the hormesis), but instead is used as a starting point to probe for possible justifications.

The most significant study on the subject involved an accidental contamination of the support structure of an apartment block in Taiwan with Cobalt 60. The results of the study showed clear improvements in the health of the inhabitants — however, many other causes could be at fault.

Misinterpretation and exploitation

It must be noted that the activation of defensive repair mechanisms at doses around 0.1 Sv — from which the low dose responses are extrapolated in the linear no-threshold model — would have resulted in under-estimation of the negative effects of radiation at doses in the vicinity of background radiation (about 0.024 Sv/year); the existence of previously unknown radiation-specific repair mechanisms may lead to stricter or laxer standards on radiation exposure, depending on the doses at which the repair mechanisms activate. Hormesis, however, is primarily associated with advocacy of laxer standards.

Radiation hormesis has some similarities to well-known pseudoscience topics such as homeopathy, and is often misunderstood to mean "radiation is good for you". Furthermore, several woo-meisters have exploited the possible existence of a "healing effect" to revive radioactive quackery. In reality, if this effect does exist, it is in all likelihood only preventive and cannot help with existing ailments. Because of these associations, radiation hormesis is often dismissed as ridiculous.

The hypothesis is often discussed by nuclear power proponents. Their lunatic faction considers it completely true and proven, and ignore that it's not accepted by international authorities. Arthur Robinson is an example.

Professional wingnut Ann Coulter has taken a shine to this theory as well, stating that the radiation released during the Fukushima disaster is healthy and would prevent cancer. A fund-raising campaign was started to fly her to the reactor so she could demonstrate this, but she never took anyone up on their offer. If radiation hormesis is true, this is a possibility for civilians, but certainly not for emergency response workers, some of which have been exposed to doses known to be harmful.

External links

• Is exposure to small amounts of radiation beneficial, Straight Dope
• Ann Coulter vs. Physics: Guess who wins?, Respectful Insolence, cached in 2012