Radiation hormesis
[8][9] There is limited evidence that exposures around this dose level will cause negative subclinical health impacts to neural development.
"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.
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.
[24] 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.
Quoting results from literature research,[13][14] they furthermore claim that approximately 40% of laboratory studies on cell cultures and animals indicate some degree of chemical or radiobiological hormesis, and state: ...its existence in the laboratory is beyond question and its mechanism of action appears well understood.They go on to outline a growing body of research that illustrates that the human body is not a passive accumulator of radiation damage but it actively repairs the damage caused via a number of different processes, including:[15][19] Furthermore, increased sensitivity to radiation induced cancer in the inherited condition Ataxia-telangiectasia like disorder, illustrates the damaging effects of loss of the repair gene Mre11h resulting in the inability to fix DNA double-strand breaks.
[28] 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".
[34] 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.
[41] However, there is currently insufficient evidence at hand to suggest that the bystander effect promotes carcinogenesis in humans at low doses.
[44] The group of experts concluded: 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.In addition, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) wrote in its 2000 report:[45] 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.
"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.
[46][17] 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.
[48] 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.
[49] 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).
This non-linear DNA damage response casts doubt on the general assumption that any amount of ionizing radiation is harmful and additive.
"[50] An early study on mice exposed to low dose of radiation daily (0.11 R per day) suggest that they may outlive control animals.
[53] In another rodent study, Sakai and collaborators found that (1 mGy/h) gamma irradiation prevents the development of cancer (induced by chemical means, injection of methylcholanthrene).
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.
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.
[62][64] 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.
