Risk of death flat­tens out af­ter 105

Max­i­mum hu­man life­spans are set to in­crease, con­cludes an Ital­ian study.

Cosmos - - Digest -

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.

CREDIT: ROBERT RICCI / GETTY IMAGES

Re­searchers pre­dict Jeanne Cal­ment’s record life­span of 122 will be bro­ken.

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