Is Chronic Radiation an Effective Prophylaxis Against Cancer

An extraordinary incident occurred 20 years ago in Taiwan. Recycled steel, accidentally contaminated with cobalt-60 (half-life: 5.3 y), was formed into construction steel for more than 180 buildings, which 10,000 persons occupied for 9 to 20 years. They unknowingly received radiation doses that averaged 0.4 Svoa icollective dosei of 4,000 person-Sv. Based on the observed seven cancer deaths, the cancer mortality rate for this population was assessed to be 3.5 per 100,000 person-years. Three children were born with congenital heart malformations, indicating a prevalence rate of 1.5 cases per 1,000 children under age 19. The average spontaneous cancer death rate in the general population of Taiwan over these 20 years is 116 persons per 100,000 person-years. Based upon partial official statistics and hospital experience, the prevalence rate of congenital malformation is 23 cases per 1,000 children. Assuming the age and income distributions of these persons are the same as for the general population, it appears that significant beneficial health effects may be associated with this chronic radiation exposure. The findings of this study are such a departure from expectations, based on International Commission on Radiological Protection (ICRP) criteria, that we believe that they ought to be carefully reviewed by other, independent organizations and that population data not available to the authors be provided, so that a fully qualified, epidemiologically valid analysis can be made. Many of the confounding factors that limit other studies used to date, such as those of the A-bomb survivors, the Mayak workers, and the Chernobyl evacuees, are not present in this population exposure. It should be one of the most important events on which to base radiation-protection standards. The data on reduced cancer mortality and congenital malformations are compatible with the phenomenon of radiation hormesis, an adaptive response of biological organisms to low levels of radiation stress or damagena modest overcompensation to a disruptionnresulting in improved fitness. Recent assessments of more than a century of data have led to the formulation of a wellfounded scientific model of this phenomenon. The experience of these 10,000 persons suggests that longterm exposure to radiation, at a dose rate of the order of 50 mSv (5 rem) per year, greatly reduces cancer mortality, which is a major cause of death in North America. Medical scientists and organizations may wish to seriously assess this and other current evidence in deciding whether chronic radiation could be an effective agent for enhancing defenses against cancer.