Review of the effect of reduced levels of background radiation on living organisms

It is well understood that all life is subject to continuous low levels of ionizing radiation, most prominently from the natural background of the biosphere, differing appreciably in particular situations across the surface of the globe. Added to this, albeit in much more isolated situations inclusive of particular workplaces and different environments, are exposures from ionizing radiations traced to human activities. Accordingly, studies of the effects of background-level radiations are subject to complex multifactorial influences. The radiation safety regulations and limits for lower levels of exposure are based on extrapolation from more elevated doses and dose rates, embodied in the linear no-threshold (LNT) model. The LNT model assumes the relationship between biological effects and radiation dose at low levels to be linear, all doses in excess of normal background carrying risk. Substantiated for high dose exposures, the validity of the model is unknown for low doses, the elucidation of possible beneficial hormetic and adaptive effects remaining a challenge. Herein, an overview of the effect on organisms of reduced low-levels of radiations is presented using available evidence and discussion of theoretical possibilities.