The plateau of human mortality: Demography of longevity pioneers

Abstract

Theories about biological limits to life span and evolutionary shaping of human longevity depend on facts about mortality at extreme ages, but these facts have remained a matter of debate. Do hazard curves typically level out into high plateaus eventually, as seen in other species, or do exponential increases persist? In this study, we estimated hazard rates from data on all inhabitants of Italy aged 105 and older between 2009 and 2015 (born 1896-1910), a total of 3836 documented cases. We observed level hazard curves, which were essentially constant beyond age 105. Our estimates are free from artifacts of aggregation that limited earlier studies and provide the best evidence to date for the existence of extreme-age mortality plateaus in humans.

Figure 1:

Yearly hazards on a logarithmic scale for the cohort of Italian women born in 1904, from the Human Mortality Database (blue) and from ISTAT data beyond age 105 (orange). Panel a (left): closeup with 95% confidence intervals based solely on single-cohort data; Panel b (right): broad view with estimated plateau beyond 105 (black dashed line) and 95% confidence bands (orange) predicted from the model parameters based on the full ISTAT database, along with a straight-line prediction (black) from fitting a Gompertz model to ages 65 to 80.

Figure 2:

Cumulative hazard beyond age 105 (orange) with non-parametric confidence bands for the cohort of Italian women born 1904. The straight lines are the translation to cumulative hazards of the estimated plateau predicted from ISTAT data, under a constant hazard (light blue) and a Gom- pertz hazard model (blue).