Can Low-Level Ionizing Radiation Do Us Any Harm?

The current system of radiological protection relies on the linear no-threshold (LNT) hypothesis of cancer risk due to humans being exposed to ionizing radiation (IR). Under this tenet, effects of low doses (i.e. of those not exceeding 100 mGy or 0.1 mGy/min. of X- or gamma-rays for acute and chronic exposures, respectively) are evaluated by downward linear extrapolation from regions of higher doses and dose rates where harmful effects are actually observed. However, evidence accumulated over many years clearly indicates that exposure of humans to low doses of radiation does not cause any harm and often promotes health. In this review, we discuss results of some epidemiological analyses, clinical trials and controlled experimental animal studies. Epidemiological data indicate the presence of a threshold and departure from linearity at the lowest dose ranges. Experimental studies clearly demonstrate the qualitative difference between biological mechanisms and effects at low and at higher doses of IR. We also discuss the genesis and the likely reasons for the persistence of the LNT tenet, despite its scientific implausibility and deleterious social consequences. It is high time to replace the LNT paradigm by a scientifically based dose-effect relationship where realistic quantitative hormetic or threshold models are exploited.