LIFE-SPAN SHORTENING

Evidence of life shortening by ionizing radiation in experimental mammals had already been accumulated as as early as 20 years ago, so that the first interpretative models could be formulated and discussed. Much more factual evidence has been discussed in the literature since then, and several models based on different approaches have been considered. From a short review of experimental data and of some of the published models, it is concluded that very few experiments are in fact available which attempt to explain the overall life shortening effect by breaking it down into all recognizable causes of death. This may be considered as the most serious limitation to the general validity of mechanistic interpretations based on the apparent linearity of life shortening as a function of dose, for single acute exposures. In this communication, the analysis of the data collected at Casaccia attempts to separate terminal disease classes with high probability of being lethal from all the other recognized pathology at death. The frequencies of the various lethal diseases show different patterns as a function of dose, so that the linear life shortening may be the result of some type of fortuitous balance between lethal disease classes at the various dose levels investigated, up to and including 9 Gy. It is also suggested that the analysis of latency times, approximated by the estimates of age specific death rates for specified diseases, may be a powerful tool in late effect studies, particularly in cases where small differences in the level of specific effects may be obscured by the concomitant presence of competing risks and of differences in life expectancy. © 1979.