Can recent Berkeley findings help us to find a solution to the paradox of cancer incidence in high natural background radiation areas of Ramsar, Iran?

According to the report published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in 2000, Ramsar city in northern Iran, has some inhabited areas with the highest known natural background radiation levels in the world (1). The annual radiation absorbed dose in high background radiation areas (HBRAs) of Ramsar is extraordinary high, reaching 260 mSv that is 13 times higher than the current annual dose limit of 20 mSv suggested by the ICRP for radiation workers. On the other hand, indoor radon concentration in some regions of HBRAs of Ramsar is up to 31 kBq m-3(2), a concentration that is much higher than the action level recommended by the U.S. Environmental Protection Agency (EPA) (148 Bq m-3 or 4 pCi/L). Considering high levels of public exposures to ionizing radiation in the residents of HBRAs of Ramsar, some experts have recently suggested the need for an effective remedial action program (2). The residents of HBRAs of Ramsar and their ancestors have been exposed to extraordinary levels of natural radiation over many generations. Therefore, if a radiation dose reaching 260 mSv y-1 is detrimental to health causing genetic abnormalities or an increased risk of cancer, it should be evident in these people. The first report on the induction of biopositive biological responses (i.e. adaptive response) in the residents of HBRAs dates back to 2002 (3). Mortazavi et al. have previously shown that the highest lung cancer mortality rate in HBRAs of Ramsar was in a district with normal levels of radon while the lowest lung cancer mortality rate was in another district with the highest concentrations of radon in the dwellings (4). However, it should be noted that due to the statistical limitations of the cancer studies in HBRAs of Ramsar, only a long-term study can provide considerable number of person-years of observation (the population who live in the HBRAs of Ramsar is estimated to be about 2000 individuals) (5, 6).