Radiation Hormesis Overview*

Evidence of health benefits and longer average life-span following low-dose irradiation should replace fear, “all radiation is harmful,” and “the perception of harm” as the basis for action in the 21 century. Hormesis is the excitation, or stimulation, by small doses of any agent in any system. Large doses inhibit. “Low dose” is defined as any dose between ambient levels of radiation and the threshold that marks the boundary between biopositive and bionegative effects. That threshold negates the “linear no threshold” (LNT) paradigm. This overview summarizes almost 3,000 reports on stimulation by low-dose irradiation. “Hormesis with Ionizing Radiation” presented evidence of increased vigor in plants, bacteria, invertebrates and vertebrates. Most physiologic reactions in living cells are stimulated by low doses of ionizing radiation. This evidence of radiogenic metabolism (metabolism promoted by ionizing radiation) includes enzyme induction, photosynthesis, respiration and growth. Radiation hormesis in immunity decreases infection and premature death in radiation exposed populations. Increased immune competence is a major factor in the increased average life-span of populations exposed to low-dose irradiation. “Radiation Hormesis” presented evidence for radiation hormesis in major physiologic functions of vertebrates. Evidence of radiation hormesis in reproduction emphasizes the safety of low-dose irradiation. “Low-Level Radiation Health Effects: Compiling the Data” summarizes recent papers on radiation hormesis. *Taken from a lecture given at ICONE-7, Tokyo, April, 1999. The author acknowledges with thanks the critical reading of this manuscript by Pauline Luckey and Dan Crockett. During the previous decades, statistically significant evidence showed that whole body exposures of humans to low doses of ionizing radiation decreased total cancer mortality rates. This is based on information compiled from 7 million person-years of exposed and control workers in nuclear shipyard and atomic bomb plants in Canada, Great Britain and the United States. Other human experiences with unusual exposures confirm radiation hormesis in cancer mortality. A variety of external sources are beneficial. Internal sources (plutonium, radium and radon) are also effective. The conclusions have both personal and national significance. Ionizing radiation is a benign environmental agent at background levels. We live with a subclinical deficiency of ionizing radiation. Low doses of ionizing radiation significantly decrease premature cancer death. Health benefits should replace risk and death as the guide for safe exposures to ionizing radiation. Safe supplementation with ionizing radiation would provide a new plateau of health.