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| Splitting more than hairs|
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.
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 variety of systems including the immune system — the latter approach to justification of the hormesis tries to escape the physical implausibility of hormesis effect at near-background levels by changing the proposed mechanism to involve 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 fraction 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.
- Is exposure to small amounts of radiation beneficial, Straight Dope
- Ann Coulter vs. Physics: Guess who wins?, Respectful Insolence, cached in 2012
- Aurengo et al. Dose-effect relationships and estimation of the carcinogenic effects of low doses of ionizing radiation. Académie des Sciences [Academy of Sciences] - Académie nationale de Médecine [National Academy of Medicine]
- P. Duport. A database of cancer induction by low-dose radiation in mammals: overview and initial observations. International Journal of Low Radiation 2003 - Vol. 1, No.1 pp. 120 - 131
- Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2, National Research Council
- Biological effects at low radiation doses, UNSCEAR report, paragraph 541
- Brenner DJ. http://www.ncbi.nlm.nih.gov/pubmed/19820460 Center for Radiological Research, Columbia University Medical Center, 630 West 168th Street, New York, NY 10032, USA.
- L E FEINENDEGEN Evidence for beneficial low level radiation effects and radiation hormesis
- Liu SZ, Liu WH, Sun JB.Radiation hormesis: its expression in the immune system. Health Phys. 1987 May;52(5):579-83.
- Effects of Cobalt-60 Exposure on Health of Taiwan Residents Suggest New Approach Needed in Radiation Protection
- Examples:   
- A Glowing Report on Radiation by Ann Coulter