Late-life mortality deceleration (mortality plateau)

Late-life mortality deceleration — the mortality plateau — is the observed phenomenon in which the age-specific hazard of death ceases its exponential Gompertz-law acceleration and flattens into an approximately constant rate, typically from around 105 years onward. Barbi et al. (2018, Science), using administrative records of all 3,836 Italians aged 105 or older between 2009 and 2015, reported an essentially flat hazard curve with an annual death probability of approximately 47–48% (baseline hazard ≈ 0.645), concluding that biological limits to lifespan may be more elastic than previously assumed. A leading mechanistic explanation invokes population heterogeneity: cohorts at extreme ages are disproportionately composed of biologically resilient individuals, so selective survival — rather than genuine slowing of cellular aging — produces the apparent plateau in aggregate hazard (the frailty-selection effect formalized by Vaupel and colleagues). The finding is contested: Gavrilov and Gavrilova (2019, PLOS Biology) showed by simulation that age-reporting errors above 105 can generate spurious deceleration even in perfectly Gompertzian data, implicating inadequate birth-record validation. Dang et al. (2023, Demographic Research), using French cohort data followed from age 105, found no plateau: the Gompertz slope parameter remained significantly positive beyond 105, indicating death rates continue to rise. These studies illustrate that extreme-age mortality dynamics are highly sensitive to data quality, national context, and cohort structure.