Risk of death flattens out after 105
Maximum human lifespans are set to increase, concludes an Italian study.
It’s no longer extraordinary to meet a centenarian. The average lifespan has skyrocketed over the past century but what about maximum lifespan?
Are we likely to see anyone break Jeanne Calment’s record of 122 years, 164 days, set in 1997?
That’s a question that has researchers disagreeing.
Now in a paper published in Science last June, statistician Elisabetta Barbi at Sapienza University of Rome, suggests we will indeed see Calment’s record broken. Her study is based on new data from a group of Italians aged over 105 that suggests their risk of dying has levelled out.
Arguments about maximum life span revolve around the maths of mortality. In 1825 British mathematician and actuary Benjamin Gompertz deduced that after the age of 30, the chance of death increases exponentially. So if a 30-year-old has a 0.1% chance of dying, by the time they’re 60, the risk has vaulted to beyond 1%. With those rapidly worsening odds, the chance of humans achieving extreme ages looked poor. But back in 1825, Gompertz had a sparse data set of elderly people to study.
Since then some researchers, beginning in the 1930s, noticed that as humans reach old age, their mortality risk seems to slow down. Similar findings were observed with some animals, particularly insects. One theory is that that the select group of individuals who reach extreme old age have better genes, so rather than a slowing of their mortality risk, they may have had a lower risk from the get-go.
While most researchers agree on the insect data, when it comes to humans there’s been vehement disagreement over whether we’re really seeing ‘mortality deceleration’ at advanced ages. Some studies of elderly populations see it; others don’t.
Adjudicating this debate hinges on the quality of the data sets for people of advanced old age. Even though we’ve been seeing more of them in recent decades, there have been questions around the accuracy of their birthdays - there’s a well-known tendency to gild the lily about extreme old age.
Furthermore, combining data from different populations can also create problems because of differences in health care. Barbi’s data set is the most reliable used to date. It comes from the Italian National Institute of Statistics that collated survival figures between 2009 and 2015 for every Italian aged over 105. All 3,836 subjects had a birth certificate, a survival certificate to verify they were indeed still alive, and for 2,883 of them, a death certificate.
The Barbi team found that while death rates do rise exponentially until the age of 80, they decelerate thereafter and plateau on or about the age of 105. For the group born in 1904, for example, that levelling out occurs with an annual probability of dying of 47.5%.
That being the case, with the global pool of people aged over 80 exploding, the prediction is that there will be more and more stayers in the longevity race to break the limit set by Calment. The authors conclude “that a limit, if any, has not been reached”.
Is this the final word? Not likely. Geneticist Jan Vijg at Albert Einstein College of Medicine in New York, points out that the Italian data set, though high quality, is still small. And while he acknowledges some slowing of the death rate, he is not convinced it is flattening.
Moreover his own study, published in Nature in 2016, shows that the 30 year streak of smashing lifespan records seen between the 1970s to the 1990s, appears to have come to an end. Indeed for 21 years Jeanne Calment has remained unbeaten. “With the explosion of centenarians, we should have seen it by now,” says Vijg.