The Concept of Biologic Half‐life in Relation to Senescence

Abstract

The half-life of the biologic processes of aging can be calculated accurately. Since the processes change more rapidly in early life, the half-life (time required for half the process) occurs very early, even before the individual is born. Data on the change in tissue water percentage and in the basal metabolic rate are illustrative.The half-life is of great interest to both the gerontologist and the internist since it indicates the paramount importance of the inherent initial material in the individual. The obstetrician and the pediatrician have tremendous responsibilities to see that the individual is well maintained in early life so that he may retain the great biologically competitive thrust with which he is born, because by the time of birth he has already aged half or more than he will ever age.In discussing such subjects as kinetics and the relationship of time to various phenomena, it is often convenient to speak of the half-life. The half-life is the length of time required for half of a phenomenon to take place. This concept is particularly useful when the phenomenon under consideration does not follow linear behavior with time.As outlined in earlier papers (1-5), the development of senescence is not linear. Senescence is continuous; it starts with the conception of the individual, and in its progress throughout life it is more rapid at the beginning than afterward. All evidence to date indicates that the processes of aging proceed in hyperbolic fashion. Possibly certain equations which describe these events have an exponential form instead of a power form.One of the classic examples of half-life is the decomposition of radioactive material. If one starts with a given amount of radium, the easiest way to monitor its decomposition is to calculate it in terms of half-life, since the process is so slow that the length of time that it would take for completion approaches infinity. In cases in which the end-point of the phenomenon is not known, it is well to use the concept of the half-life. In biology this concept is used less often than in physical chemistry, but is equally valid.It is important to realize that doubling the half-life does not necessarily * Address: 1103 Regent Street, Madison, Wisconsin 53715. 974