Editing Radiation hormesis

{{Short description|Hypothesis regarding low doses of ionizing radiation on health}}
[[File:Radiations at low doses.gif|294px|thumb|right|Alternative assumptions for the extrapolation of the cancer risk vs. radiation dose to low-dose levels, given a known risk at a high dose: supra-linearity (A), linear (B), linear-quadratic (C) and [[hormesis]] (D).]]
'''Radiation hormesis''' is the [[hypothesis]] that low doses of [[ionizing radiation]] (within the region of and just above [[Background radiation|natural background levels]]) are beneficial, stimulating the activation of [[DNA repair|repair mechanisms]] that protect against [[disease]], that are not activated in absence of ionizing radiation. The reserve repair mechanisms are hypothesized to be sufficiently effective when stimulated as to not only cancel the detrimental effects of ionizing radiation but also inhibit disease not related to radiation exposure (see [[hormesis]]).<ref name="Calabrese">{{cite journal |doi=10.1038/421691a |title=Toxicology rethinks its central belief |year=2003 |last1=Calabrese |first1=Edward J |last2=Baldwin |first2=Linda A |journal=Nature |volume=421 |issue=6924 |pages=691–92 |pmid=12610596|bibcode = 2003Natur.421..691C |s2cid=4419048 }}</ref><ref>{{cite journal |doi=10.1259/bjr/63353075 |title=Evidence for beneficial low level radiation effects and radiation hormesis |year=2005 |last1=Feinendegen |first1=L E |journal=British Journal of Radiology |volume=78 |issue=925 |pages=3–7 |pmid=15673519}}</ref><ref name ="Kaiser">{{cite journal |doi=10.1126/science.302.5644.376 |title=HORMESIS: Sipping from a Poisoned Chalice |year=2003 |last1=Kaiser |first1=J. |journal=Science |volume=302 |issue=5644 |pages=376–79 |pmid=14563981|s2cid=58523840 }}</ref><ref>{{cite journal |doi=10.2307/3433927|pmid=9539019|jstor=3433927|title=The Adaptive Response in Radiobiology: Evolving Insights and Implications|journal=Environmental Health Perspectives|volume=106|pages=277–83|year=1998|last1=Wolff|first1=Sheldon|issue=Suppl 1 |pmc=1533272}}</ref> It has been a mainstream concept since at least 2009.<ref>{{cite book |last=Allison |first=Wade |author-link=Wade Allison |title=Radiation and Reason: The Impact of Science on a Culture of Fear |year=2009 |publisher=York Publishing Services |location=York, England |isbn=978-0-9562756-1-5 |page=2}}</ref>{{Unreliable source?|date=April 2024}}

While the effects of high and acute doses of ionising radiation are easily observed and understood in humans (''e.g.'' [[Atomic bombings of Hiroshima and Nagasaki|Japanese atomic bomb]] survivors), the effects of low-level radiation are very difficult to observe and highly controversial. This is because the baseline cancer rate is already very high and the risk of developing cancer fluctuates 40% because of individual life style and environmental effects,<ref>{{Cite web
| title = WHO Cancer Fact sheet N°297
| access-date = 2011-04-29
| url =https://www.who.int/mediacentre/factsheets/fs297/en/}}</ref><ref name=parkin2011>{{Cite journal |doi=10.1038/bjc.2011.489 |title=16. The fraction of cancer attributable to lifestyle and environmental factors in the UK in 2010 |year=2011 |last1=Parkin |first1=D M |last2=Boyd |first2=L |last3=Walker |first3=L C |journal=British Journal of Cancer |volume=105 |pages=S77–81 |pmid=22158327 |pmc=3252065 |issue=Suppl 2}}</ref> obscuring the subtle effects of low-level radiation. An acute effective dose of 100 [[Sievert|millisieverts]] may increase cancer risk by ~0.8%. However, children are particularly sensitive to radioactivity, with [[childhood leukemia]]s and [[Childhood cancer|other cancers]] increasing even within natural and man-made background radiation levels (under 4&nbsp;mSv cumulative with 1&nbsp;mSv being an average annual dose from terrestrial and cosmic radiation, excluding [[radon]] which primarily doses the lung).<ref>{{cite journal|last1=Kendall|title=A record-based case-control study of natural background radiation and the incidence of childhood leukaemia and other cancers in Great Britain during 1980–2006|journal=Leukemia|date=January 2013|volume=27 |issue=1|pages=3–9|display-authors=etal|doi=10.1038/leu.2012.151|pmid=22766784|pmc=3998763}}</ref><ref>{{cite journal |vauthors=Spycher BD, Lupatsch JE, Zwahlen M, Röösli M, Niggli F, Grotzer MA, Rischewski J, Egger M, Kuehni CE |title=Background ionizing radiation and the risk of childhood cancer: a census-based nationwide cohort study |journal=Environ. Health Perspect. |volume=123 |issue=6 |pages=622–28 |date=June 2015 |pmid=25707026 |pmc=4455589 |doi=10.1289/ehp.1408548 }}</ref> There is limited evidence that exposures around this dose level will cause negative subclinical health impacts to neural development.<ref>{{cite journal|last1=Pasqual|title=Neurodevelopmental effects of low dose ionizing radiation exposure: A systematic review of the epidemiological evidence.|journal=Environment International|year=2020|volume=136|page=105371|doi=10.1016/j.envint.2019.105371|pmid=32007921|display-authors=etal|doi-access=free|bibcode=2020EnInt.13605371P |hdl=10230/46812|hdl-access=free}}</ref> Students born in regions of higher [[Chernobyl disaster|Chernobyl fallout]] performed worse in secondary school, particularly in mathematics. "Damage is accentuated within families (i.e., siblings comparison) and among children born to parents with low education..." who often don't have the resources to overcome this additional health challenge.<ref>{{cite journal|last1=Almond|title=Chernobyl's subclinical legacy: Prenatal exposure to radioactive fallout and school outcomes in Sweden.|journal=Columbia University|date=2007|display-authors=etal|url=http://www.columbia.edu/~le93/Chernobyl.pdf}}</ref>

Hormesis remains largely unknown to the public. Government and regulatory bodies disagree on the existence of radiation hormesis and research points to the "severe problems and limitations" with the use of hormesis in general as the "principal dose-response default assumption in a risk assessment process charged with
ensuring public health protection."<ref>{{cite journal |vauthors=Kitchin KT, Drane JW |title=A critique of the use of hormesis in risk assessment |journal=Hum Exp Toxicol |volume=24 |issue=5 |pages=249–53 |date=May 2005 |pmid=16004188 |doi=10.1191/0960327105ht520oa |bibcode=2005HETox..24..249K |s2cid=9105845 |url=https://zenodo.org/record/894716 }}</ref>

Quoting results from a literature database research, the Académie des Sciences – Académie nationale de Médecine ([[French Academy of Sciences]] – [[French Academy of Medicine|National Academy of Medicine]]) stated in their 2005 report concerning the effects of low-level radiation that many laboratory studies have observed radiation hormesis.<ref name = "Calabrese2">{{cite journal |doi=10.1016/j.taap.2004.02.007 |title=Hormesis: From marginalization to mainstream |year=2004 |last1=Calabrese |first1=Edward J |journal=Toxicology and Applied Pharmacology |volume=197 |issue=2 |pages=125–36 |pmid=15163548}}</ref><ref name = "Duport">{{cite journal |doi=10.1504/IJLR.2003.003488 |title=A database of cancer induction by low-dose radiation in mammals: Overview and initial observations |year=2003 |last1=Duport |first1=P. |journal=International Journal of Low Radiation |volume=1 |pages=120–31}}</ref> However, they cautioned that it is not yet known if radiation hormesis occurs outside the laboratory, or in humans.<ref name="Aurengo">{{Cite journal
| author = Aurengo
| title = Dose-effect relationships and estimation of the carcinogenic effects of low doses of ionizing radiation
| publisher = Académie des Sciences & Académie nationale de Médecine
| date = 2005-03-30
| citeseerx = 10.1.1.126.1681
}}</ref>

Reports by the [[United States National Research Council]] and the [[National Council on Radiation Protection and Measurements]] and the [[United Nations Scientific Committee on the Effects of Atomic Radiation]] (UNSCEAR) argue<ref>UNSCEAR 2000 Report Vol. II: Sources and Effects of Ionizing Radiation: [http://www.unscear.org/docs/reports/annexg.pdf Annex G: Biological effects at low radiation doses].</ref> that there is no evidence for hormesis in humans and in the case of the National Research Council hormesis is outright rejected as a possibility.<ref name=BEIR_VII>{{harvnb|BEIR VII Phase 2|2006}}</ref> Therefore, estimating [[linear no-threshold model]] (LNT) continues to be the model generally used by regulatory agencies for human radiation exposure.

== Proposed mechanism and ongoing debate ==
[[Image:Hormesis dose response graph.svg|220px|thumb|left|A very low dose of a chemical agent may trigger from an [[organism]] the opposite response to a very high dose.]]
Radiation hormesis proposes that radiation exposure comparable to and just above the natural [[background radiation|background level of radiation]] is not harmful but beneficial, while accepting that much higher levels of radiation are hazardous. Proponents of radiation hormesis typically claim that radio-protective responses in cells and the immune system not only counter the harmful effects of radiation but additionally act to inhibit spontaneous cancer not related to radiation exposure. Radiation hormesis stands in stark contrast to the more generally accepted [[linear no-threshold model]] (LNT), which states that the radiation dose-risk relationship is linear across all doses, so that small doses are still damaging, albeit less so than higher ones. Opinion pieces on chemical and radiobiological hormesis appeared in the journals [[Nature (journal)|Nature]]<ref name="Calabrese"/> and [[Science (journal)|Science]]<ref name ="Kaiser"/> in 2003.

Assessing the risk of radiation at low doses (<100 [[Sievert|mSv]]) and low dose rates (<0.1 [[Sievert|mSv]].min<sup>−1</sup>) is highly problematic and controversial.<ref name=Mullenders>{{cite journal |doi=10.1038/nrc2677 |title=Assessing cancer risks of low-dose radiation |year=2009 |last1=Mullenders |first1=Leon |last2=Atkinson |first2=Mike |last3=Paretzke |first3=Herwig |last4=Sabatier |first4=Laure |last5=Bouffler |first5=Simon |journal=Nature Reviews Cancer |volume=9 |issue=8 |pages=596–604 |pmid=19629073|s2cid=10610131 }}</ref><ref name=Tubiana>{{cite journal |doi=10.1148/radiol.2511080671 |title=The Linear No-Threshold Relationship is Inconsistent with Radiation Biologic and Experimental Data1 |year=2009 |last1=Tubiana |first1=M. |last2=Feinendegen |first2=L. E. |last3=Yang |first3=C. |last4=Kaminski |first4=J. M. |journal=Radiology |volume=251 |pages=13–22 |pmid=19332842 |issue=1 |pmc=2663584}}</ref> While [[epidemiological]] studies on populations of people exposed to an acute dose of high level radiation such as [[Hibakusha|Japanese atomic bomb survivors]] ({{nihongo|hibakusha|被爆者}}) have robustly upheld the [[linear no-threshold model|LNT]] (mean dose ~210 mSv),<ref name=Samartzis>{{cite journal |doi=10.2106/JBJS.J.00256 |title=Exposure to Ionizing Radiation and Development of Bone Sarcoma: New Insights Based on Atomic-Bomb Survivors of Hiroshima and Nagasaki |year=2011 |last1=Samartzis |first1=Dino |journal=The Journal of Bone and Joint Surgery. American Volume |volume=93 |issue=11 |pages=1008–15 |pmid=21984980 |last2=Nishi |first2=N |last3=Hayashi |first3=M |last4=Cologne |first4=J |last5=Cullings |first5=HM |last6=Kodama |first6=K |last7=Miles |first7=EF |last8=Funamoto |first8=S |last9=Suyama |first9=A|last10=Soda |first10=M |last11=Kasagi |first11=F |display-authors=8 |citeseerx=10.1.1.1004.393 }}</ref> studies involving low doses and low dose rates have failed to detect any increased cancer rate.<ref name="Tubiana"/> This is because the baseline cancer rate is already very high (~42 of 100 people will be diagnosed in their lifetime) and it fluctuates ~40% because of lifestyle and environmental effects,<ref name="parkin2011"/><ref name=Boice2012>{{cite journal |doi=10.1088/0952-4746/32/1/N33 |title=Radiation epidemiology: A perspective on Fukushima |year=2012 |last1=Boice Jr |first1=John D |journal=Journal of Radiological Protection |volume=32 |pages=N33–40 |pmid=22395193 |issue=1|s2cid=250881575 }}</ref> obscuring the subtle effects of low level radiation. Epidemiological studies may be capable of detecting elevated cancer rates as low as 1.2 to 1.3 ''i.e.'' 20% to 30% increase. But for low doses (1–100 mSv) the predicted elevated risks are only 1.001 to 1.04 and excess cancer cases, if present, cannot be detected due to confounding factors, errors and biases.<ref name=Boice2012/><ref name=Boice>{{cite journal |bibcode=2010JRP....30..115B |title=Invited Editorial: Uncertainties in studies of low statistical power Uncertainties in studies of low statistical power |last1=Boice |first1=John D. |volume=30 |year=2010 |pages=115–20 |journal=Journal of Radiological Protection |doi=10.1088/0952-4746/30/2/E02 |pmid=20548136 |issue=2|s2cid=36270712 |doi-access=free }}</ref><ref>{{cite journal | doi = 10.2203/dose-response.09-019.Fornalski | pmid=20585442 | title = The Healthy Worker Effect and Nuclear Industry Workers | journal = Dose-Response| volume = 8| issue = 2| pages = 125–47| year = 2010 | last1 = Fornalski | first1 = K. W. | last2 = Dobrzyński | first2 = L. | pmc=2889508}}</ref>

In particular, variations in smoking prevalence or even accuracy in reporting smoking cause wide variation in excess cancer and measurement error bias. Thus, even a large study of many thousands of subjects with imperfect smoking prevalence information will fail to detect the effects of low level radiation than a smaller study that properly compensates for smoking prevalence.<ref>{{cite journal |doi=10.1097/00004032-199012000-00004 |title=Design Issues in Epidemiologic Studies of Indoor Exposure to Rn and Risk of Lung Cancer |year=1990 |last1=Lubin |first1=Jay H. |last2=Samet |first2=Jonathan M. |last3=Weinberg |first3=Clarice|author3-link=Clarice Weinberg |journal=Health Physics |volume=59 |issue=6 |pages=807–17 |pmid=2228608}}</ref> Given the absence of direct epidemiological evidence, there is considerable debate as to whether the dose-response relationship <100 mSv is supralinear, linear (LNT), has a threshold, is ''sub-linear'', or whether the coefficient is negative with a sign change, i.e. a hormetic response.

The radiation [[adaptive response]] seems to be a main origin of the potential hormetic effect. The theoretical studies indicate that the adaptive response is responsible for the shape of dose-response curve and can transform the linear relationship (LNT) into the hormetic one.<ref>{{cite journal | doi = 10.1667/RR14302.1 |pmid=27588596 | title = Modeling of Irradiated Cell Transformation: Dose- and Time-Dependent Effects | journal = Radiation Research | volume = 186| issue = 4| pages = 396–406| year = 2016 | last1 = Dobrzyński | first1 = L. | last2 = Fornalski | first2 = K. W. | last3 = Socol | first3 = Y. | last4 = Reszczyńska | first4 = J. M.| bibcode = 2016RadR..186..396D |s2cid=41033441 }}</ref><ref>{{cite journal |doi=10.1103/PhysRevE.99.022139 | vauthors = Fornalski KW |title=Radiation adaptive response and cancer: from the statistical physics point of view |volume=99 |issue=2 |journal=Physical Review E |date=2019| page = 022139 | pmid = 30934317 | bibcode = 2019PhRvE..99b2139F | s2cid = 91187501 }}</ref>

While most major consensus reports and government bodies currently adhere to LNT,<ref>{{cite journal |doi=10.1097/00004032-199810000-00001 |title=From Chimney Sweeps to Astronauts |year=1998 |last1=Hall |first1=Eric J. |journal=Health Physics |volume=75 |issue=4 |pages=357–66 |pmid=9753358|s2cid=30056597 }}</ref> the 2005 [[French Academy of Sciences]]-[[Académie Nationale de Médecine|National Academy of Medicine]]'s report concerning the effects of low-level radiation rejected LNT as a scientific model of [[carcinogenic]] risk at low doses.<ref name="Aurengo"/>

<blockquote>Using LNT to estimate the carcinogenic effect at doses of less than 20 mSv is not justified in the light of current radiobiologic knowledge.</blockquote>

They consider there to be several dose-effect relationships rather than only one, and that these relationships have many variables such as target tissue, radiation dose, dose rate and individual sensitivity factors. They request that further study is required on low doses (less than 100 [[Sievert|mSv]]) and very low doses (less than 10 [[Sievert|mSv]]) as well as the impact of tissue type and age. The Academy considers the LNT model is only useful for regulatory purposes as it simplifies the administrative task. Quoting results from literature research,<ref name="Calabrese2"/><ref name="Duport"/> they furthermore claim that approximately 40% of laboratory studies on cell cultures and animals indicate some degree of chemical or radiobiological hormesis, and state:

<blockquote>...its existence in the laboratory is beyond question and its mechanism of action appears well understood.</blockquote>

They go on to outline a growing body of research that illustrates that the human body is not a passive accumulator of [[ionizing radiation|radiation]] damage but it actively repairs the damage caused via a number of different processes, including:<ref name="Aurengo"/><ref name="Tubiana"/>

* Mechanisms that mitigate [[reactive oxygen]] species generated by ionizing radiation and [[oxidative stress]].
* [[Apoptosis]] of radiation damaged cells that may undergo [[tumorigenesis]] is initiated at only few mSv.
* Cell death during [[meiosis]] of radiation damaged cells that were unsuccessfully repaired.
* The existence of a [[cellular signaling]] system that alerts neighboring cells of cellular damage.
* The activation of [[Enzyme|enzymatic]] [[DNA repair]] mechanisms around 10 mSv.
* Modern [[DNA microarray]] studies which show that numerous [[genes]] are activated at [[Ionizing radiation|radiation]] doses well below the level that [[mutagenesis]] is detected.
* [[Ionizing radiation|Radiation]]-induced [[tumorigenesis]] may have a threshold related to damage density, as revealed by experiments that employ blocking grids to thinly distribute [[Ionizing radiation|radiation]].
* A large increase in tumours in [[immunosuppressed]] individuals illustrates that the immune system efficiently destroys aberrant cells and nascent tumors.

Furthermore, increased sensitivity to radiation induced cancer in the inherited condition [[Ataxia-telangiectasia#Differential Diagnosis|Ataxia-telangiectasia like disorder]], illustrates the damaging effects of loss of the repair gene [[HMre11|Mre11h]] resulting in the inability to fix DNA double-strand breaks.<ref name=Stewart1>{{cite journal |doi=10.1016/S0092-8674(00)81547-0 |title=The DNA Double-Strand Break Repair Gene hMRE11 is Mutated in Individuals with an Ataxia-Telangiectasia-like Disorder |year=1999 |last1=Stewart |first1=G |journal=Cell |volume=99 |issue=6 |pages=577–87 |pmid=10612394 |last2=Maser |first2=RS |last3=Stankovic |first3=T |last4=Bressan |first4=DA |last5=Kaplan |first5=MI |last6=Jaspers |first6=NG |last7=Raams |first7=A |last8=Byrd |first8=PJ |last9=Petrini |first9=JH|last10=Taylor |first10=A. M. |display-authors=8 |doi-access=free }}</ref>

The BEIR-VII report argued that, "the presence of a true dose threshold demands totally error-free DNA damage response and repair." The specific damage they worry about is double strand breaks (DSBs) and they continue, "error-prone nonhomologous end joining (NHEJ) repair in postirradiation cellular response, argues strongly against a DNA repair-mediated low-dose threshold for cancer initiation".<ref>{{harvnb|BEIR VII Phase 2|2006|p=245}}</ref> Recent research observed that DSBs caused by [[CAT scans]] are repaired within 24 hours and DSBs may be more efficiently repaired at low doses, suggesting that the risk of ionizing radiation at low doses may not be directly proportional to the dose.<ref name="Löbrich2005">{{cite journal |bibcode=2005PNAS..102.8984L |title=In vivo formation and repair of DNA double-strand breaks after computed tomography examinations |last1=Löbrich |first1=Markus |last2=Rief |first2=Nicole |last3=Kühne |first3=Martin |last4=Heckmann |first4=Martina |last5=Fleckenstein |first5=Jochen |last6=Rübe |first6=Christian |last7=Uder |first7=Michael |volume=102 |year=2005 |pages=8984–89 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0501895102 |issue=25 |pmid=15956203 |pmc=1150277|doi-access=free }}</ref><ref name=Neumaier2011>{{cite journal |bibcode=2012PNAS..109..443N |title=Evidence for formation of DNA repair centers and dose-response nonlinearity in human cells |last1=Neumaier |first1=T. |last2=Swenson |first2=J. |last3=Pham |first3=C. |last4=Polyzos |first4=A. |last5=Lo |first5=A. T. |last6=Yang |first6=P. |last7=Dyball |first7=J. |last8=Asaithamby |first8=A. |last9=Chen |first9=D. J. |last10=Bissell |first10=M. J. |last11=Thalhammer |first11=S. |last12=Costes |first12=S. V. |volume=109 |year=2012 |pages=443–48 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.1117849108 |issue=2 |pmid=22184222 |pmc=3258602|display-authors=8 |doi-access=free }}</ref> However, it is not known if low-dose ionizing radiation stimulates the repair of DSBs not caused by ionizing radiation ''i.e.'' a hormetic response. 
 
Radon gas in homes is the largest source of radiation dose for most individuals and it is generally advised that the concentration be kept below 150 Bq/m³ (4 pCi/L).<ref>{{cite web |url=http://www.surgeongeneral.gov/pressreleases/sg01132005.html |title=Surgeon General Releases National Health Advisory On Radon |access-date=28 November 2008 |publisher=US HHS Office of the Surgeon General |date=January 12, 2005  |archive-url=https://web.archive.org/web/20080516195401/http://www.surgeongeneral.gov/pressreleases/sg01132005.html |archive-date=16 May 2008 }}</ref> A recent retrospective case-control study of lung cancer risk showed substantial cancer rate reduction between 50 and 123 Bq per cubic meter relative to a group at zero to 25 Bq per cubic meter.<ref>{{cite journal |doi=10.1097/01.HP.0000288561.53790.5f |title=Case-Control Study of Lung Cancer Risk from Residential Radon Exposure in Worcester County, Massachusetts |year=2008 |last1=Thompson |first1=Richard E. |last2=Nelson |first2=Donald F. |last3=Popkin |first3=Joel H. |last4=Popkin |first4=Zenaida |journal=Health Physics |volume=94 |issue=3 |pages=228–41 |pmid=18301096|s2cid=21134066 }}</ref> This study is cited as evidence for hormesis, but a single study all by itself cannot be regarded as definitive. Other studies into the effects of domestic [[radon]] exposure have not reported a hormetic effect; including for example the respected "Iowa Radon Lung Cancer Study" of Field et al. (2000), which also used sophisticated radon exposure [[dosimetry]].<ref>{{cite journal |doi=10.1093/oxfordjournals.aje.a010153 |title=Residential Radon Gas Exposure and Lung Cancer: The Iowa Radon Lung Cancer Study |year=2000 |last1=Field |first1=R. W. |last2=Steck |first2=D. J. |last3=Smith |first3=B. J. |last4=Brus |first4=C. P. |last5=Fisher |first5=E. L. |last6=Neuberger |first6=J. S. |last7=Platz |first7=C. E. |last8=Robinson |first8=R. A. |last9=Woolson |first9=R. F. |last10=Lynch |first10=C. F. |journal=American Journal of Epidemiology |volume=151 |issue=11 |pages=1091–102 |pmid=10873134|display-authors=8 |doi-access=free }}</ref> In addition, Darby et al. (2005) argue that radon exposure is negatively correlated with the tendency to smoke and environmental studies need to accurately control for this; people living in urban areas where smoking rates are higher usually have lower levels of radon exposure due to the increased prevalence of multi-story dwellings.<ref name=Darby>{{cite journal |doi=10.1136/bmj.38308.477650.63 |title=Radon in homes and risk of lung cancer: Collaborative analysis of individual data from 13 European case-control studies |year=2005 |last1=Darby |first1=S |journal=BMJ |volume=330 |issue=7485 |page=223 |pmid=15613366 |last2=Hill |first2=D |last3=Auvinen |first3=A |last4=Barros-Dios |first4=JM |last5=Baysson |first5=H |last6=Bochicchio |first6=F |last7=Deo |first7=H |last8=Falk |first8=R |last9=Forastiere |first9=F |last10=Hakama |first10=M |last11=Heid |first11=I |last12=Kreienbrock |first12=L |last13=Kreuzer |first13=M |last14=Lagarde |first14=F |last15=Mäkeläinen |first15=I |last16=Muirhead |first16=C |last17=Oberaigner |first17=W |last18=Pershagen |first18=G |last19=Ruano-Ravina |first19=A |last20=Ruosteenoja |first20=E |last21=Rosario |first21=A. S. |last22=Tirmarche |first22=M |last23=Tomásek |first23=L |last24=Whitley |first24=E |last25=Wichmann |first25=H. E. |last26=Doll |first26=R |pmc=546066|display-authors=8 }}</ref>  When doing so, they found a significant increase in lung cancer amongst smokers exposed to radon at doses as low as 100 to 199 Bq m<sup>−3</sup> and warned that smoking greatly increases the risk posed by radon exposure ''i.e.'' reducing the prevalence of smoking would decrease deaths caused by radon.<ref name=Darby/><ref name=Mendez>{{cite journal |doi=10.2105/AJPH.2009.189225 |title=The Impact of Declining Smoking on Radon-Related Lung Cancer in the United States |year=2011 |last1=Méndez |first1=David |last2=Alshanqeety |first2=Omar |last3=Warner |first3=Kenneth E. |last4=Lantz |first4=Paula M. |last5=Courant |first5=Paul N. |journal=American Journal of Public Health |volume=101 |issue=2 |pages=310–14 |pmid=21228294 |pmc=3020207}}</ref> However, the discussion about the opposite experimental results is still going on,<ref>{{cite journal |last=Fornalski |first=K. W. |author2=Adams, R. |author3=Allison, W. |author4=Corrice, L. E. |author5=Cuttler, J. M. |author6=Davey, Ch. |author7=Dobrzyński, L. |author8=Esposito, V. J. |author9=Feinendegen, L. E. |author10=Gomez, L. S. |author11=Lewis, P. |author12=Mahn, J. |author13=Miller, M. L. |author14=Pennington, Ch. W. |author15=Sacks, B. |author16=Sutou, S. |author17=Welsh, J. S. |pmid=26223888 |title=The assumption of radon-induced cancer risk |year=2015 |journal=Cancer Causes & Control |doi=10.1007/s10552-015-0638-9 |issue=26 |volume=10 |pages=1517–18|s2cid=15952263 }}</ref> especially the popular US and German studies have found some hormetic effects.<ref>{{cite journal |author=Cohen BL |title=Test of the linear-no threshold theory of radiation carcinogenesis for inhaled radon decay products |journal=Health Phys |volume=68 |issue=2|year=1995 |pmid=7814250 |url=http://www.phyast.pitt.edu/%7Eblc/LNT-1995.PDF |doi=10.1097/00004032-199502000-00002 |pages=157–74|s2cid=41388715 }}</ref><ref>{{cite journal |last=Becker |first=K. |pmid=19330110 |pmc=2651614 |title=Health Effects of High Radon Environments in Central Europe: Another Test for the LNT Hypothesis? |year=2003 |journal=Nonlinearity Biol Toxicol Med |issue=1 |volume=1 |pages=3–35|doi=10.1080/15401420390844447 }}</ref>

Furthermore, particle microbeam studies show that passage of even a single alpha particle (e.g. from radon and its progeny) through cell nuclei is highly mutagenic,<ref name="pmid9108052">{{cite journal |bibcode=1997PNAS...94.3765H |title=Mutagenic Effects of a Single and an Exact Number of α Particles in Mammalian Cells |last1=Hei |first1=Tom K. |last2=Wu |first2=Li-Jun |last3=Liu |first3=Su-Xian |last4=Vannais |first4=Diane |last5=Waldren |first5=Charles A. |last6=Randers-Pehrson |first6=Gerhard |volume=94 |year=1997 |pages=3765–70 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.94.8.3765 |pmid=9108052 |issue=8 |pmc=20515|doi-access=free }}</ref> and that alpha radiation may have a higher mutagenic effect at low doses (even if a small fraction of cells are hit by alpha particles) than predicted by linear no-threshold model, a phenomenon attributed to [[bystander effect (radiobiology)|bystander effect]].<ref>{{Cite journal |bibcode=2000PNAS...97.2099Z |title=Induction of a bystander mutagenic effect of alpha particles in mammalian cells |last1=Zhou |first1=Hongning |last2=Randers-Pehrson |first2=Gerhard |last3=Waldren |first3=Charles A. |last4=Vannais |first4=Diane |last5=Hall |first5=Eric J. |last6=Hei |first6=Tom K. |volume=97 |year=2000 |pages=2099–104 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.030420797 |issue=5 |pmid=10681418 |pmc=15760|doi-access=free }}</ref> However, there is currently insufficient evidence at hand to suggest that the bystander effect promotes [[carcinogenesis]] in humans at low doses.<ref name=Blyth&Sykes2011>{{cite journal |doi=10.1667/RR2548.1 |title=Radiation-Induced Bystander Effects: What Are They, and How Relevant Are They to Human Radiation Exposures? |year=2011 |last1=Blyth |first1=Benjamin J. |last2=Sykes |first2=Pamela J. |journal=Radiation Research |volume=176 |issue=2 |pages=139–57 |pmid=21631286|bibcode=2011RadR..176..139B |s2cid=38879987 }}</ref>

==Statements by leading nuclear bodies==

Radiation hormesis has not been accepted by either the [[United States National Research Council]],<ref name=BEIR_VII/> or the [[National Council on Radiation Protection and Measurements (NCRP)]].<ref>[http://www.ncrppublications.org/index.cfm?fm=Product.AddToCart&pid=6714063164 NCRP Report No. 136 – Evaluation of the Linear-Nonthreshold Dose-Response Model for Ionizing Radiation]</ref> In May 2018, the NCRP published the report of an interdisciplinary group of radiation experts who critically reviewed 29 high-quality epidemiologic studies of populations exposed to radiation in the low dose and low dose-rate range, mostly published within the last 10 years.<ref>{{citation | publisher=National Council on Radiation Protection and Measurements|year=2018| url=https://ncrponline.org/wp-content/themes/ncrp/Pub_announcements/Commentary_No27_overview.pdf | title=NCRP Commentary No. 27 [Overview]: Implications of Recent Epidemiologic Studies for the Linear-Nonthreshold Model and Radiation Protection}}</ref> The group of experts concluded:

<blockquote> The recent epidemiologic studies support the continued use of the LNT model for radiation protection. This is in accord with judgments by other national and international scientific committees, based on somewhat older data, that no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes than the LNT model.</blockquote>

In addition, the [[United Nations Scientific Committee on the Effects of Atomic Radiation]] (UNSCEAR) wrote in its 2000 report:<ref>UNSCEAR 2000 Report Vol. II: Sources and Effects of Ionizing Radiation: [http://www.unscear.org/docs/reports/annexg.pdf Annex G: Biological effects at low radiation doses]. p. 160, para. 541.</ref>
<blockquote> 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.</blockquote>

This is a reference to the fact that very low doses of radiation have only marginal impacts on individual health outcomes. It is therefore difficult to detect the 'signal' of decreased or increased morbidity and mortality due to low-level radiation exposure in the 'noise' of other effects. 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.<ref>{{cite news| url=http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=11340 | title=Low Levels of Ionizing Radiation May Cause Harm | publisher=National Academy of Sciences | last=Vines | first=Vanee |author2=Petty, Megan  | date=2005-06-29 | access-date=2010-01-27}}</ref><ref name=BEIR_VII/>

{{blockquote|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.}}

== Studies of low-level radiation ==

=== Cancer rates and very high natural background gamma radiation at Kerala, India ===

Kerala's [[monazite]] sand (containing a third of the world's economically recoverable [[List of countries by thorium resources|reserves]] of radioactive [[thorium]]) emits about 8&nbsp;micro[[sievert]]s per hour of gamma radiation, 80&nbsp;times the dose rate equivalent in London, but a decade-long study of 69,985 residents published in Health Physics in 2009 "showed no excess cancer risk from exposure to terrestrial gamma radiation. The excess relative risk of cancer excluding leukemia was estimated to be −0.13 per Gy (95% CI: −0.58, 0.46)", indicating no statistically significant positive or negative relationship between background radiation levels and cancer risk in this sample.<ref name=Nair2009>{{cite journal |doi=10.1097/01.HP.0000327646.54923.11 |title=Background Radiation and Cancer Incidence in Kerala, India – Karanagappally Cohort Study |year=2009 |last1=Nair |first1=Raghu Ram K. |last2=Rajan |first2=Balakrishnan |last3=Akiba |first3=Suminori |last4=Jayalekshmi |first4=P. |last5=Nair |first5=M. Krishnan |last6=Gangadharan |first6=P. |last7=Koga |first7=Taeko |last8=Morishima |first8=Hiroshige |last9=Nakamura |first9=Seiichi |last10=Sugahara |first10=Tsutomu |journal=Health Physics |volume=96 |pages=55–66 |pmid=19066487 |issue=1|s2cid=24657628 |display-authors=8 }}</ref>

=== Cultures ===

Studies in cell cultures can be useful for finding mechanisms for biological processes, but they also can be criticized for not effectively capturing the whole of the living organism.

A study by E. I. Azzam suggested that pre-exposure to radiation causes cells to turn on protection mechanisms.<ref>{{cite journal| author=Azzam, E. I. |journal=Radiation Research |year=1994 |volume=138 |pmid=8146320 |pages=S28–S31 |doi=10.2307/3578755 |title=Radiation-Induced Adaptive Response for Protection against Micronucleus Formation and Neoplastic Transformation in C3H 10T1/2 Mouse Embryo Cells |last2=Raaphorst |first2=G. P. |last3=Mitchel |first3=R. E. J. |issue=1 |jstor=3578755 |bibcode=1994RadR..138S..28A}}</ref> A different study by de Toledo and collaborators has shown that irradiation with gamma rays increases the concentration of glutathione, an antioxidant found in cells.<ref>{{cite journal |doi=10.1667/RR0640.1 |title=Adaptive Responses to Low-Dose/Low-Dose-Rate γ Rays in Normal Human Fibroblasts: The Role of Growth Architecture and Oxidative Metabolism |year=2006 |last1=De Toledo |first1=Sonia M. |last2=Asaad |first2=Nesrin |last3=Venkatachalam |first3=Perumal |last4=Li |first4=Ling |last5=Howell |first5=Roger W. |last6=Spitz |first6=Douglas R. |last7=Azzam |first7=Edouard I. |journal=Radiation Research |volume=166 |issue=6 |pages=849–857 |pmid=17149977|bibcode=2006RadR..166..849D |s2cid=31148344 }}</ref>

In 2011, an ''in vitro'' study led by S. V. Costes showed in time-lapse images a strongly non-linear response of certain cellular repair mechanisms called radiation-induced foci (RIF). The study found that low doses of radiation prompted higher rates of RIF formation than high doses, and that after low-dose exposure RIF continued to form after the radiation had ended. Measured rates of RIF formation were 15&nbsp;RIF/[[Gray (unit)|Gy]] at 2&nbsp;Gy, and 64&nbsp;RIF/Gy at 0.1&nbsp;Gy.<ref name="Neumaier2011" /> These results suggest that low dose levels of [[ionizing radiation]] may not increase cancer risk directly proportional to dose and thus contradict the linear-no-threshold standard model.<ref name=HC24865 >{{Cite web |url=http://www.healthcanal.com/public-health-safety/24865-New-Take-Impacts-Low-Dose-Radiation.html |title = New Take on Impacts of Low Dose Radiation |date = 20 December 2011}}</ref> [[Mina Bissell]], a world-renowned breast-cancer researcher and collaborator in this study stated: "Our data show that at lower doses of ionizing radiation, DNA repair mechanisms work much better than at higher doses. This non-linear DNA damage response casts doubt on the general assumption that any amount of ionizing radiation is harmful and additive."<ref name=HC24865/>

=== Animals ===
An early study on mice exposed to low dose of radiation daily (0.11&nbsp;[[roentgen (unit)|R]] per day) suggest that they may outlive control animals.<ref>{{cite journal |title=Long-Term Effects of Acute and Chronic Irradiation in Mice. I. Survival and Tumor Incidence Following Chronic Irradiation of 0.11&nbsp;R Per Day |author1=Egon Lorenz |author2=Joanne Weikel Hollcroft |author3=Eliza Miller |author4=Charles C. Congdon |author5=Robert Schweisthal |journal=Journal of the National Cancer Institute |volume=15 |issue=4 |date=1 February 1955 |pages=1049–1058 |doi=10.1093/jnci/15.4.1049 |pmid=13233949}}</ref> A study by Otsuka and collaborators found hormesis in animals.<ref>{{cite journal |doi=10.1667/RR0561.1 |title=Activation of Antioxidative Enzymes Induced by Low-Dose-Rate Whole-Body γ Irradiation: Adaptive Response in Terms of Initial DNA Damage |year=2006 |last1=Otsuka |first1=Kensuke |last2=Koana |first2=Takao |last3=Tauchi |first3=Hiroshi |last4=Sakai |first4=Kazuo |journal=Radiation Research |volume=166 |issue=3 |pages=474–78 |pmid=16953665|bibcode=2006RadR..166..474O |s2cid=44742877 }}</ref> Miyachi conducted a study on mice and found that a 200&nbsp;mGy X-ray dose protects mice against both further X-ray exposure and ozone gas.<ref>{{cite journal |pmid=10817047 |year=2000 |last1=Miyachi |first1=Y |title=Acute mild hypothermia caused by a low dose of X-irradiation induces a protective effect against mid-lethal doses of X-rays, and a low level concentration of ozone may act as a radiomimetic |volume=73 |issue=867 |pages=298–304 |journal=[[The British Journal of Radiology]] |doi=10.1259/bjr.73.867.10817047}}</ref> In another rodent study, Sakai and collaborators found that (1&nbsp;mGy/[[hour|h]]) gamma irradiation prevents the development of cancer (induced by chemical means, injection of [[methylcholanthrene]]).<ref>{{cite journal |doi=10.1016/S0531-5131(01)00861-5 |title=Suppressive effect of long-term low-dose rate gamma-irradiation on chemical carcinogenesis in mice |year=2002 |last1=Sakai |first1=Kazuo |last2=Iwasaki |first2=Toshiyasu |last3=Hoshi |first3=Yuko |last4=Nomura |first4=Takaharu |last5=Oda |first5=Takeshi |last6=Fujita |first6=Kazuko |last7=Yamada |first7=Takeshi |last8=Tanooka |first8=Hiroshi |journal=International Congress Series |volume=1236 |pages=487–490}}
</ref>

In a 2006 paper,<ref>{{cite journal |doi=10.1667/RR0682.1 |title=The Effect of Dose Rate on Radiation-Induced Neoplastic TransformationIn Vitroby Low Doses of Low-LET Radiation |year=2006 |last1=Elmore |first1=E. |last2=Lao |first2=X.-Y. |last3=Kapadia |first3=R. |last4=Redpath |first4=J. L. |journal=[[Radiation Research]] |volume=166 |issue=6 |pages=832–838 |pmid=17149982 |bibcode=2006RadR..166..832E |s2cid=24775008 }}</ref> a dose of 1&nbsp;Gy was delivered to the cells (at constant rate from a radioactive source) over a series of lengths of time. These were between 8.77 and 87.7 hours, the abstract states for a dose delivered over 35 hours or more (low dose rate) no transformation of the cells occurred. Also for the 1&nbsp;Gy dose delivered over 8.77 to 18.3 hours that the biological effect (neoplastic transformation) was about "1.5 times less than that measured at high dose rate in previous studies with a similar quality of [X-ray] radiation". Likewise it has been reported that fractionation of gamma irradiation reduces the likelihood of a neoplastic transformation.<ref>{{cite journal |doi=10.1093/carcin/5.2.193 |title=Multifractionation of <sup>60</sup>Co gamma-rays reduces neoplastic transformation in vitro |year=1984 |last1=Hill |first1=C. K. |last2=Han |first2=A. |last3=Buonaguro |first3=F. |last4=Elkind |first4=M. M. |journal=Carcinogenesis |volume=5 |issue=2 |pages=193–197 |pmid=6697436}}</ref> Pre-exposure to fast neutrons and gamma rays from Cs-137 is reported to increase the ability of a second dose to induce a neoplastic transformation.<ref>{{cite journal |doi=10.1080/09553009214552011 |title=Enhanced Sensitivity to Neoplastic Transformation by <sup>137</sup>Cs γ-rays of Cells in the G2-/M-phase Age Interval |year=1992 |last1=Cao |first1=J. |last2=Wells |first2=R. L. |last3=Elkind |first3=M. M. |journal=[[International Journal of Radiation Biology]] |volume=62 |issue=2 |pages=191–199 |pmid=1355513}}</ref>

Caution must be used in interpreting these results, as it noted in the BEIR VII report, these pre-doses can also increase cancer risk:<ref name=BEIR_VII/>

{{blockquote|In chronic low-dose experiments with dogs (75&nbsp;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).}}

However, 75&nbsp;mGy/d cannot be accurately described as a low dose rate&nbsp;– it is equivalent to over 27 sieverts per year. The same study on dogs showed no increase in cancer nor reduction in life expectancy for dogs irradiated at 3&nbsp;mGy/d.<ref>{{Cite web |url=http://www.nuclearsafety.gc.ca/eng/pdfs/Presentations/Guest-Speakers/2013/20130625-Cuttler-CNSC-Fukushima-and-beneficial-effects-low-radiation.pdf |author=Jerry M. Cuttler Cuttler & Associates Inc. |work=Canadian Nuclear Safety Commission Ottawa, Ontario 2013 June 25 |title=Fukushima and Beneficial Health Effects of Low Radiation |access-date=2014-08-24 |archive-date=2014-07-10 |archive-url=https://web.archive.org/web/20140710235841/http://nuclearsafety.gc.ca/eng/pdfs/Presentations/Guest-Speakers/2013/20130625-Cuttler-CNSC-Fukushima-and-beneficial-effects-low-radiation.pdf }}</ref>

=== Humans ===

==== Effects of slightly increased radiation level ====

In long-term study of Chernobyl disaster liquidators<ref>{{cite web |url=https://www.rsu.lv/sites/default/files/dissertations/JReste_Promocijas_darba_kopsavilkums_EN.pdf |author=Jeļena Reste |title=THE AGING ASPECTS OF HUMANS PROTRACTEDLY EXPOSED TO IONIZING RADIATION |work=Summary of Doctoral Thesis Speciality. Occupational and Environmental Medicine |publisher=Rīga Stradiņš University |date=2013 |location=Riga}}</ref> was found that: "During current research paradoxically longer telomeres were found among persons, who have received heavier long-term irradiation." and "Mortality due to oncologic diseases was lower than in general population in all age groups that may reflect efficient health care of this group." Though in conclusion interim results were ignored and conclusion followed [[Linear no-threshold model|LNT]] hypothesis: "The signs of premature aging were found in Chernobyl disaster clean-up workers; moreover, aging process developed in heavier form and at younger age in humans, who underwent greater exposure to ionizing radiation."

A study of survivors of the [[Atomic bombings of Hiroshima and Nagasaki|Hirsohima atomic bomb explosion]] yielded similar results.<ref>{{cite journal |last1=Sutou |first1=Shizuyo |title=Black rain in Hiroshima: a critique to the Life Span Study of A-bomb survivors, basis of the linear no-threshold model |journal=Genes and Environment |pages=1 |language=en |doi=10.1186/s41021-019-0141-8 |date=1 January 2020|volume=42 |issue=1 |doi-access=free |pmid=31908690 |bibcode=2020GeneE..42....1S |pmc=6937943 }}</ref>

====Effects of sunlight exposure====
In an Australian study which analyzed the association between solar [[UV]] exposure and DNA damage, the results indicated that although the frequency of cells with [[chromosome]] breakage increased with increasing [[sun exposure]], the misrepair of [[DNA]] strand breaks decreased as sun exposure was heightened.<ref>{{cite journal |doi=10.1093/mutage/ges026 |title=Sunlight and vitamin D affect DNA damage, cell division and cell death in human lymphocytes: A cross-sectional study in South Australia |year=2012 |last1=Nair-Shalliker |first1=V. |last2=Fenech |first2=M. |last3=Forder |first3=P. M. |last4=Clements |first4=M. S. |last5=Armstrong |first5=B. K. |journal=Mutagenesis |volume=27 |issue=5 |pages=609–614 |pmid=22547344 |doi-access= }}</ref>

====Effects of cobalt-60 exposure====
The health of the inhabitants of radioactive apartment buildings in [[Taiwan]] has received prominent attention. In 1982, more than 20,000 tons of steel was accidentally contaminated with [[cobalt-60]], and much of this radioactive steel was used to build apartments and exposed thousands of Taiwanese to gamma radiation levels of up to >1000 times background (average 47.7&nbsp;mSv, maximum 2360&nbsp;mSv excess cumulative dose). The radioactive contamination was discovered in 1992.

A seriously flawed 2004 study compared the building's younger residents with the much older general population of Taiwan and determined that the younger residents were less likely to have been diagnosed with cancer than older people; this was touted as evidence of a radiation hormesis effect.<ref name="Hwang1">{{cite journal |doi=10.1080/09553000601085980 |title=Cancer risks in a population with prolonged low dose-rate γ-radiation exposure in radiocontaminated buildings, 1983–2002 |year=2006 |last1=Hwang |first1=S.-L. |last2=Guo |first2=H.-R. |last3=Hsieh |first3=W.-A. |last4=Hwang |first4=J.-S. |last5=Lee |first5=S.-D. |last6=Tang |first6=J.-L. |last7=Chen |first7=C.-C. |last8=Chang |first8=T.-C. |last9=Wang |first9=J.-D. |last10=Chang |first10=W. P. |journal=International Journal of Radiation Biology |volume=82 |issue=12 |pages=849–858 |pmid=17178625 |s2cid=20545464 }}</ref><ref name="Chen-Age">{{Cite conference
| last = Chen
| first = C. Y.
| author2=Y. J. Chen
| title = The Social Migration Effect Toward Population Aging-The Application of Perston's Rate of Change of a Population's Mean Age Improvement Model in Taiwan
| conference = The 23rd Conference of the European Network for Housing Research
| access-date = 2012-05-09
| year = 2011
| url = http://140.116.240.46/ISAD/files/P28941029-a.pdf
}}</ref> (Older people have much higher cancer rates even in the absence of excess radiation exposure.)

In the years shortly after exposure, the total number cancer cases have been reported to be either lower than the society-wide average or slightly elevated.<ref name=":0">{{Cite book |title=Casarett & Doull's essentials of toxicology |date=2021 |author1=Curtis D. Klaassen |author2=John B. Watkins, III |isbn=978-1-260-45229-7 |edition=4th |publisher=McGraw-Hill Education |location=New York |page=459 |oclc=1159605376}}</ref><ref>{{Cite book |title=Environmental pollutant exposures and public health |date=2021 |publisher=CPI Group |isbn=978-1-83916-043-1 |editor-last=Harrison |editor-first=Roy M. |location=London |page=50 |oclc=1204222461 |quote=Cancer incidence in a cohort of ~6250 people has been studied, and marginally raised levels of cancer in relation to assessed doses have been reported, although there are a number of uncertainties in the student, including lack of control for confounding factors such as smoking}}</ref> Leukaemia and thyroid cancer were substantially elevated.<ref name="Hwang1" /><ref name=":0" /> When a lower rate of "all cancers" was found, it was thought to be due to the exposed residents having a higher [[socioeconomic status]], and thus overall healthier lifestyle.<ref name="Hwang1" /><ref name=":0" /> Additionally, Hwang, et al. cautioned in 2006 that [[leukaemia]] was the first cancer type found to be elevated amongst the survivors of the Hiroshima and Nagasaki bombings, so it could be decades before any increase in more common cancer types is seen.<ref name="Hwang1" />

Besides the excess risks of leukaemia and thyroid cancer, a later publication notes various DNA anomalies and other health effects among the exposed population:<ref name="Hwang2008">{{cite journal |doi=10.1667/RR0732.1 |title=Estimates of Relative Risks for Cancers in a Population after Prolonged Low-Dose-Rate Radiation Exposure: A Follow-up Assessment from 1983 to 2005 |year=2008 |last1=Hwang |first1=Su-Lun |last2=Hwang |first2=Jing-Shiang |last3=Yang |first3=Yi-Ta |last4=Hsieh |first4=Wanhua A. |last5=Chang |first5=Tien-Chun |last6=Guo |first6=How-Ran |last7=Tsai |first7=Mong-Hsun |last8=Tang |first8=Jih-Luh |last9=Lin |first9=I-Feng |last10=Chang |first10=Wushou Peter |journal=Radiation Research |volume=170 |issue=2 |pages=143–148 |pmid=18666807 |bibcode=2008RadR..170..143H |s2cid=41512364 |url=http://ntur.lib.ntu.edu.tw/bitstream/246246/246866/-1/index.html }}</ref>
<blockquote>
There have been several reports concerning the radiation effects on the exposed population, including cytogenetic analysis that showed increased micronucleus frequencies in peripheral lymphocytes in the exposed population, increases in acentromeric and single or multiple centromeric cytogenetic damages, and higher frequencies of chromosomal translocations, rings and dicentrics. Other analyses have shown persistent depression of peripheral leucocytes and neutrophils, increased eosinophils, altered distributions of lymphocyte subpopulations, increased frequencies of lens opacities, delays in physical development among exposed children, increased risk of thyroid abnormalities, and late consequences in hematopoietic adaptation in children.
</blockquote>
People living in these buildings also experienced infertility.<ref>{{Cite journal |last1=Lin |first1=C.-M. |last2=Chang |first2=W. P. |last3=Doyle |first3=P. |last4=Wang |first4=J.-D. |last5=Lee |first5=L.-T. |last6=Lee |first6=C. L. |last7=Chen |first7=P.-C. |date=March 2010 |title=Prolonged time to pregnancy in residents exposed to ionising radiation in cobalt-60-contaminated buildings |journal=Occupational and Environmental Medicine |volume=67 |issue=3 |pages=187–195 |doi=10.1136/oem.2008.045260 |issn=1470-7926 |pmid=19773284|s2cid=40448903 }}</ref>

==== Radon therapy ====
{{Further|Health effects of radon#Bathing}}
Intentional exposure to water and air containing increased amounts of [[radon]] is perceived as therapeutic, and "radon spas" can be found in United States, Czechia, Poland, Germany, Austria and other countries.

==Effects of no radiation==

Given the uncertain effects of low-level and very-low-level radiation, there is a pressing need for quality research in this area. An expert panel convened at the 2006 Ultra-Low-Level Radiation Effects Summit at Carlsbad, New Mexico, proposed the construction of an Ultra-Low-Level Radiation [[laboratory]].<ref name="ORION">"Ultra-Low-Level Radiation Effects Summit." January 2006. ORION International Technologies, Inc. (ORION) and sponsored by the U.S. Department of Energy's Waste Isolation Pilot Plant (WIPP) 03 Apr. 2008. [http://www.orionint.com/projects/ullre.cfm]</ref>  The laboratory, if built, will investigate the effects of almost ''no radiation'' on [[laboratory animals]] and [[cell culture]]s, and it will compare these groups to [[control group]]s exposed to natural radiation levels. Precautions would be made, for example, to remove [[potassium-40]] from the food of laboratory animals. The expert panel believes that the Ultra-Low-Level Radiation laboratory is the only [[experiment]] that can explore with authority and confidence the effects of low-level radiation; that it can confirm or discard the various radiobiological effects proposed at low radiation levels e.g. [[Linear no-threshold model|LNT]], threshold and radiation hormesis.<ref>http://www.orionint.com/ullre/report-2006.pdf{{full citation needed|date=October 2013}}</ref>

The first preliminary results of the effects of almost no-radiation on cell cultures was reported by two research groups in 2011 and 2012; researchers in the US studied cell cultures protected from radiation in a steel chamber 650 meters underground at the [[Waste Isolation Pilot Plant]] in Carlsbad, New Mexico<ref name=Smith2011>{{cite journal |doi=10.1097/HP.0b013e318208cd44 |title=Exploring Biological Effects of Low Level Radiation from the Other Side of Background |year=2011 |last1=Smith |first1=Geoffrey Battle |last2=Grof |first2=Yair |last3=Navarrette |first3=Adrianne |last4=Guilmette |first4=Raymond A. |journal=Health Physics |volume=100 |issue=3 |pages=263–65 |pmid=21595063}}</ref> and researchers in Europe proposed an experiment design to study the effects of almost no-radiation on mouse cells (pKZ1 transgenic chromosomal inversion assay), but did not carry out the experiment.<ref name=Capece2011>{{cite journal |bibcode=2012EPJP..127...37C |title=The use of pKZ1 mouse chromosomal inversion assay to study biological effects of environmental background radiation |last1=Capece |first1=D. |last2=Fratini |first2=E. |volume=127 |year=2012 |page=37 |journal=The European Physical Journal Plus |doi=10.1140/epjp/i2012-12037-7 |issue=4|s2cid=14508554 }}</ref>

==See also==
* [[Background radiation]]
* [[Dose fractionation]]
* [[Hormesis]]
* [[Radithor]]
* [[Linear no-threshold model]]
* [[Petkau effect]]
* [[Radioresistance]]
* [[Ramsar, Mazandaran]]

==References==
{{Reflist|2}}

== Further reading ==
* Sanders, Charles L. (2009). ''Radiation Hormesis and the Linear-No-Threshold Assumption''. {{ISBN|3642037194}}

==External links==
* [http://www.dose-response.org/ International Dose-Response Society]. University of Massachusetts center for research on hormesis. Many papers on radiation hormesis.
*{{cite book |url=http://books.nap.edu/catalog/11340.html |author=National Research Council |title=Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 |publisher=The National Academies Press |doi=10.17226/11340 |year=2006 |isbn=978-0-309-09156-5 |ref={{harvid|BEIR VII Phase 2|2006}}}} [http://books.nap.edu/catalog/11340.html?onpi_newsdoc062905 Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2]
* [https://web.archive.org/web/20071009101429/http://www.radpro.com/641luckey.pdf Radiation Hormesis Overview] by T. D. Luckey, who wrote a book on the subject (Luckey, T. D. (1991). ''Radiation Hormesis''. Boca Raton, FL: CRC Press. {{ISBN|0-8493-6159-1}})
* {{cite journal |bibcode=2003PNAS..10013761B |jstor=3148861 |title=Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know |last1=Brenner |first1=David J. |last2=Doll |first2=Richard |last3=Goodhead |first3=Dudley T. |last4=Hall |first4=Eric J. |last5=Land |first5=Charles E. |last6=Little |first6=John B. |last7=Lubin |first7=Jay H. |last8=Preston |first8=Dale L. |last9=Preston |first9=R. Julian |last10=Puskin |first10=J. S. |last11=Ron |first11=E. |last12=Sachs |first12=R. K. |last13=Samet |first13=J. M. |last14=Setlow |first14=R. B. |last15=Zaider |first15=M. |volume=100 |year=2003 |pages=13761–66 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.2235592100 |issue=24 |pmid=14610281 |pmc=283495|display-authors=8 |doi-access=free }}
* {{Skeptoid | id=4539 | number=539 | title=Radiation Hormesis: Is It Good for You?}}

{{Radiation}}

{{DEFAULTSORT:Radiation Hormesis}}
[[Category:Radiobiology]]
[[Category:Radiation health effects]]

[[ru:Гормезис]]