A previously unrecognized peculiarity of late-life human mortality kinetics?

Abstract

The late-life mortality kinetics in several species features the deceleration of mortality rate increase with age, which in humans starts at ca. 90 years. Being analyzed based on the Gompertz law µ(t)=µ0*e^gt with its inbuilt linearity of the dependency of lnµ(t) on t, this feature is interpreted as reflecting the heterogeneity of a population where the frailer subjects die out earlier thus increasing the proportion of those whose dying out is slower and leading to a decrease in the demographic (actuarial) rate of aging. Using Human Mortality Database data related to France, Sweden and Japan in the periods 2020 and 1920 and to the cohorts born in 1920, it is shown in the present communication that the putative deceleration of the demographic (actuarial) rate of aging in humans is preceded by an acceleration, which starts at about 65 years, reaches a peak, which at about 85 years is ca. 30% higher than the pre-acceleration level, and decelerates thereafter until 90 years at least, when the pre-acceleration level is reached. This peculiarity cannot be explained with the predominant dying out of frailer subjects at earlier ages. Its plausible explanation may be the real acceleration of the (averaged) biological aging in humans at ages above 65-70 years, which conspicuously coincide with retirement. The biological implications of this finding are discussed in terms of the generalized Gomperts-Makeham law µ(t)=C(t)+µ0e^f(t). In particular, the deceleration of mortality increase in the oldest-old subjects may be contributed to by the actual biological deceleration of aging.