protect it against carcinogenesis due to low-dose exposures of carcinogens. Ramsar, located in Iran, is often quoted as being a counter example to LNT. Based on preliminary results, it was considered as having the highest natural background radiation levels on Earth, several times higher than the ICRP-recommended radiation dose limits for radiation workers, whilst the local population did not seem to have any ill effects. However, the population of the high-radiation districts is small (about 1800 inhabitants) and only receive an average of 6 millisieverts per year, so cancer epidemiology data are too imprecise to draw any conclusions. On the other hand, there may be non-cancer effects from the background radiation such as chromosomal aberrations. At the same time in Germany and Austria, some of the most radiophobic countries, people attend "radon spas" where they voluntarily expose themselves to low-level radiation of radon for its alleged health benefits. A 2011 research of the cellular repair mechanisms support the evidence against the linear no-threshold model. According to its authors, this study published in the Proceedings of the National Academy of Sciences of the United States of America "casts considerable doubt on the general assumption that risk to ionizing radiation is proportional to dose". A 2011 review of studies addressing childhood leukaemia following exposure to ionizing radiation, including both diagnostic exposure and natural background exposure from radon, concluded that existing risk factors, excess relative risk per sievert (ERR/Sv), is "broadly applicable" to low dose or low dose-rate exposure, "although the uncertainties associated with this estimate are considerable". The study also notes that "epidemiological studies have been unable, in general, to detect the influence of natural background radiation upon the risk of childhood leukaemia" Several expert scientific panels have been convened on the accuracy of the LNT model at low dosage, and various organizations and bodies have stated their positions on this topic: Support The US Nuclear Regulatory Commission: The NRC upheld the LNT model in 2021 as a "sound regulatory basis for minimizing the risk of unnecessary radiation exposure to both members of the public and radiation workers" following challenges to the dose limit requirements contained in its regulations. In 2004 the United States National Research Council (part of the National Academy of Sciences) supported the linear no threshold model and stated regarding Radiation hormesis: In 2005 the United States National Academies' National Research Council published its comprehensive meta-analysis of low-dose radiation