Barbi E, Lagona F, Marsili M, Vaupel JW, Wachter KW. The plateau of human mortality: Demography of longevity pioneers. Science. 2018;360(6396):1459–1461. doi:10.1126/science.aat3119
At a glance
Starting from the data collected by ISTAT on about 4000 Italian people between 105 and 110 years old, a research group headed by La Sapienza University of Rome, has shown that the mortality curve in this age group stops growing. “The data studied, carefully documented – explains Elisabetta Barbi, Sapienza – lead to the conclusion that the mortality curve increases exponentially until the age of about 80 years, but then decelerates until it reaches a plateau, that is a constant trend, after 105 years”.
What is already known
According to what is known as Gompertz’s law (which the mathematician Benjamin Gompertz proposed in 1825) the probability of dying doubles every eight years. This seems to be the rule for people in their 30s to 80s, but there is no agreement among researchers about what happens at very old age mortality rates.
If the curve continues to increase exponentially it reaches a maximum limit beyond which life cannot extend, but it has also been hypothesized that the curve decelerates and slows down in later life.
The difficulty of finding data on mortality year by year and not aggregated by age group together with the phenomenon of “age exageration” are the main limits against which researchers clash in verifying these demographic models.
Design and Method
The study is based on ISTAT data including 3836 cases (463 males) of people aged 105 or older, between 2009 and 2015. For several reasons these data allow, according to the researchers, an estimation of mortality rates with an accuracy and precision not previously available.
- ISTAT has collected death, birth and survival certificates in an attempt to minimize the possibility of “age exaggeration”.
- The researchers traced individual survival trajectories from one year to the next, rather than grouping people into age groups as they had done earlier studies combining datasets.
- Focusing only on Italy, which has one of the highest per capita centenarian rates in the world, avoids the problem of variability in data collection between different sources: validation procedures have been developed for this specific population segment and meet the criteria of the International Database of Longevity (IDL) protocol.
According to the demographic model described, the mortality curve decelerates after the age of 80 and becomes constant after the age of 105 (see graph).
Another interesting finding from the research is that for the younger generation of births, mortality levels are slightly lower. Combined with the growth of super centenarians in recent years, this would indicate that longevity is continuing to increase over time and that a limit, if any, has not been reached.
The data analyzed concern the specific Italian context and it is not clear whether they can be generalized, given that previous research aggregating data from different countries has not led to the same results.
The issue of the limits of longevity has been widely debated for years: other criticisms and doubts about possible limits of this research are presented in the letters to the journal.
The main novelty of the study is that it questions the notion of a limit beyond which it is not possible to extend human life, hypothesized by previous studies, reopening the debate on longevity.
What the prospects
A plateau in mortality at an extremely advanced age has been observed in other species (fruit flies, some worms, etc.): the confirmation of this trend also in man is in line with evolutionary ageing theories.
The evolutionary theories of senescence – the theory of the accumulation of mutations and age-dependent effects of the genetic load – offer promising elements for a joint explanation of both the phases of exponential increase and this plateau. To put it simply: the more fragile subjects tend to die earlier, while the stronger or “genetically luckier” ones can live to extreme ages.
By Francesca Memini