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Radiation hormesis has been rejected by both the United States National Research Council (part of the National Academy of Sciences) and the National Council on Radiation Protection and Measurements (a body commissioned by the U.S. Congress). In addition, the United Nations Scientific Committee on the Effects of Ionizing Radiation (UNSCEAR) wrote in its most recent report 
Until the [...] uncertainties on low-dose response are resolved, the Committee believes that an increase in the risk of tumour induction proportionate to the radiation dose is consistent with developing knowledge and that it remains, accordingly, the most scientifically defensible approximation of low-dose response. However, a strictly linear dose response should not be expected in all circumstances.
The theory is explained by the hypothesis that genes that repair damage due to radiation are activated and reduce damage from other causes, which would otherwise be imperfectly repaired. There is some evidence that radiation levels of 100 mSv/year may actually be positive or at least neutral to health. Indeed there have been claims that humans live in a subclinical deficiency of ionising radiation.
 Evidence for and against
 Evidence for
One claim that many studies have focused on is that pre-exposure to low levels of radiation will protect one from a future dose including the following:
- A study has suggested that pre-exposure to radiation exerts a protective effect upon cells.
- One study found that a 200 mGy X-ray dose protects mice against both further X-ray exposure and ozone gas.
- One study found that preexposure to radiation (50 to 100 mGy for four hours) results in a small reduction of the ability of an 8 Gy dose to damage DNA in intact cells due to a shift in the cell cycle.
- One study found that moderate internal exposure to plutonium results in a reduction of the risk of cancer.
- An article in the "Townsend Letter: The Examiner of Alternative Medicine" suggested that a small dose of radiation may be beneficial.
However, none showed this benefit to last for more than 24 hours, making the usefulness questionable.
Another question is the effect of prolonged exposure to radiation on one's health. The vast preponderance of studies have upheld the linear no threshold theory, but epidemiological studies are very difficult, as an example, people with longer life-spans are more likely to get cancer, so those who are occupationally exposed have better health on average because they had a job--they are thus more likely to get cancer regardless of their exposure. As another example:
- Ramsar has naturally very high radiation (with an observed maximum of 260 mSv/year) due to its geology  but is found to have no increased cancer risk.
But the above example could be due to a lower economic status of the occupants of Ramsar.
 Evidence against
- Pilots are more prone to brain, rectal and prostate cancers whilst flight crews are twice as susceptible to breast cancer, but are healthier overall than the general public (possibly because they are healthier when selected for the job due to health screening). However there is a contrary suggestion and evidence that breast cancer in flight crews may be caused by jet lag.
 Rejecting radiation hormesis
The notion of radiation hormesis has been rejected by the National Research Council's (part of the National Academy of Sciences) 16 year long study on the Biological Effects of Ionizing Radiation. "The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial. The health risks – particularly the development of solid cancers in organs – rise proportionally with exposure" says Richard R. Monson, associate dean for professional education and professor of epidemiology, Harvard School of Public Health, Boston . See the National Acadamies Press book Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2.
- The possibility that low doses of radiation may have beneficial effects (a phenomenon often referred to as “hormesis”) has been the subject of considerable debate. Evidence for hormetic effects was reviewed, with emphasis on material published since the 1990 BEIR V study on the health effects of exposure to low levels of ionizing radiation. Although examples of apparent stimulatory or protective effects can be found in cellular and animal biology, the preponderance of available experimental information does not support the contention that low levels of ionizing radiation have a beneficial effect. The mechanism of any such possible effect remains obscure. At this time, the assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from radiation exposure at the same dose is unwarranted .
- In chronic low-dose experiments with dogs (75 mGy/d for the duration of life), vital hematopoietic progenitors showed increased radioresistance along with renewed proliferative capacity (Seed and Kaspar 1992). Under the same conditions, a subset of animals showed an increased repair capacity as judged by the unscheduled DNA synthesis assay (Seed and Meyers 1993). Although one might interpret these observations as an adaptive effect at the cellular level, the exposed animal population experienced a high incidence of myeloid leukemia and related myeloproliferative disorders. The authors concluded that “the acquisition of radioresistance and associated repair functions under the strong selective and mutagenic pressure of chronic radiation is tied temporally and causally to leukemogenic transformation by the radiation exposure” (Seed and Kaspar 1992) . See also Hormesis under "Non-acceptance".
 Cadmium poisoning as a model
It is known that many toxic metals can induce oxidative stress in tissue which may result in free radical induced damage. Also it is known that prior exposure to a small dose of cadmium can mitigate the effects of a second larger dose, this suggests that the first lower dose of the poison stimulates the DNA repair processes in the exposed tissue. 
 See also
 External links
- Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2
- Abstract of a study showing that radiation increases the rate of natural antioxidant (glutathione) production. The study found that this does not act as a radiation protection, but seems to protect against other cellular insults such as oxidation.
- History of the idea by a supporter of the concept.
- Radiation Hormesis Overview by T. D. Luckey, who literally wrote the book on the subject (Luckey, T. D. (1991). Radiation Hormesis. Boca Raton, FL: CRC Press.)
- Radiation Hormesis: Demonstrated, Deconstructed, Denied, Dismissed, and Some Implications for Public Policy by Joel M. Kauffman: "evidence is presented that chronic doses up to 100 times those of normal ambient (including medical) exposures are beneficial..."
- ^ http://books.nap.edu/catalog/11340.html Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2
- ^ http://www.ncrppublications.org/index.cfm?fm=Product.AddToCart&pid=6714063164
- ^ UNSCEAR 2000 REPORT Vol. II: Sources and Effects of Ionizing Radiation: Annex G: Biological effects at low radiation doses. page 160, paragraph 541. Available online at .
- ^ Luckey T (1999). "Nurture with ionizing radiation: a provocative hypothesis.". Nutr Cancer 34 (1): 1-11. PMID 10453435.
- ^ Azzam, E. I.: Radiation Research, 1994, 138(1), S28-S31
- ^ Miyachi, Y.: The British Journal of Radiology, 2000, 73, 298-304
- ^ Cramers, P.; Atanasova, P.; Vrolijk, H.; Darroudi, F.; van Zeeland, A. A.; Huiskamp, R.; Mullenders, L. H.; Kleinjans, J.C.: )
- ^ Kendall, G.M. et al.: Mortality and occupational exposure to radiation; First analysis of the National Registry for Radiation Workers. British Medical Journal, 1992; 304: 220.
- ^ 
- ^ http://www.ecolo.org/documents/documents_in_english/ramsar-natural-radioactivity/ramsar.html
- ^ http://news.bbc.co.uk/1/hi/health/380274.stm
- ^ http://news.bbc.co.uk/1/hi/health/154933.stm
- ^ Wahba, Z. Z.; Hernandez, L.; Issaq, H. J.; Waalkes, M. P. (1990): Involvement of sulfhydryl metabolism in tolerance to cadmium in testicular cells. Toxicology and Applied Pharmacology, 104:157-166.
- ^ Waalkes, M. P.; Perantoni, A. (1986): Isolation of a novel metal-binding protein from rat testes: characterization and distinction from metallothionein. Journal of Biological Chemistry, 261:13079-13103.
- ^ Waalkes, M. P.; Rehm, S.; Riggs, C.W.; et al. (1988): Cadmium carcinogenesis in male Wistar (Crl:(WI)BR) rats: dose-response analysis of tumor induction in the prostate and testes, and at the injection site. Cancer Research, 48:4656-4663.
- ^ Rugstad, H. E.; Norseth, T. (1975): Cadmium resistance and content of cadmium-binding protein in cultured human cells. Nature, 257:136-137.