High Natural Background Radiation Areas: A Literature Review that Reveals Systematic Adaptive Response but Controversial Data With Single Dose.

The natural radiation background contributes to the dose of ionizing radiation received by the whole population. However, the telluric component of the natural background radiation is not homogenous on Earth: while the average effective dose has been estimated to be 2.4 mSv/year worldwide, certain regions are considered as high natural background radiation areas (HBRA). To investigate the specificities of a continuous exposure to low-dose-rate irradiation, we reviewed data of the major HBRA from 98 studies published between 1973 and 2023. Three conclusions were drawn: 1) the dose received by the HBRA inhabitants is much lower than values assessed on hot spots : at Ramsar (Iran), 260 mSv/year were assessed at the highest hotspots but the maximal estimated dose-rate received by inhabitants is 80 mSv/year; 2) when DNA or chromosome breaks, cancer or accelerated aging are used as endpoints, no significant difference was observed between cells from HBRA and non-HBRA inhabitants; 3) conversely, adaptive response effect was systematically observed on ex vivo lymphocytes from HBRA inhabitants when they are exposed to a high dose ranging for 0.25 to 4 Gy. A mechanistic model based on the radiation-induced nucleoshuttling of the ATM protein provides an explanation to these last two conclusions.