It has been suggested that in very late life mortality rates flatten out and cease to increase. This effect has been observed in flies and other short-lived species, and insofar as aging is defined as an increase in mortality rate over time, it implies that old individuals cease to age. This isn't a desirable sort of agelessness, of course, as the plateaued mortality rates are very high; individuals are in poor health and do not live much longer. How might we interpret this? That all of the most harmful damage has already been done, and further accumulated damage doesn't much change the near future outcome?
In humans it is questionable as to whether there is enough data for people of 110 years and older to support any sort of rigorous conclusion about mortality rate trends in that sparse age group. The few researchers who have tried to crunch the numbers come away with quite different conclusions, depending on the details of their methodology, with the example here being one of those leaning towards an absence of a late life mortality plateau in our species.
Accurate estimates of mortality at advanced ages are essential for forecasts of population aging and for testing the predictions of competing theories of aging. They also contribute to more reliable forecasts of future longevity. Earlier studies suggest that exponential growth of mortality (Gompertz law) is followed by a period of deceleration, with slower rates of mortality increase at extreme old ages. This mortality deceleration eventually produces the "late-life mortality leveling-off" and "late-life mortality plateaus" at extreme old ages. Researchers have provided a detailed description of this phenomenon in humans and even made the first estimates for the asymptotic value of the upper limit to human mortality. The same phenomenon of "almost non-aging" survival dynamics at extreme old ages is detected in other biological species, and in some species the mortality plateau can occupy a sizable part of their life.
Studies of mortality after age 110 years are scarce because of difficulties in obtaining reliable age estimates. It was demonstrated that the age misreporting at older ages results in mortality underestimation. Also, it was found that mortality deceleration is more expressed in the case of poor-quality data than with data of better quality. Recent analysis of detailed records from the U.S. Social Security Administration Death Master File for several single-year extinct birth cohorts demonstrated that the Gompertz law fits mortality data better than other models up to ages 105-106 years. However, existing studies of mortality after age 110 years reported flat mortality, which does not grow with age.
In this paper, we analyze mortality trajectories for supercentenarians, using data on a sufficiently large sample of supercentenarians (aged 110 and older) available in the International Database on Longevity (IDL). All ages of supercentenarians in the database were subjected to careful validation. These results demonstrate that hazard rates after age 110 years do not stay constant and suggest that mortality deceleration at older ages is not a universal phenomenon. These findings may represent a challenge to the existing theories of aging and longevity, which predict constant mortality in the late stages of life. One possibility for reconciliation of the observed phenomenon and the existing theoretical consideration is a possibility of mortality deceleration and mortality plateau at very high yet unobservable ages.