Likelihood of death surprisingly falls for centenarians
Climb over the hill and head for the plateau. That, according to biologists, defines the path to extreme old age. Researchers have announced that once someone reaches 105, their yearly chances of dying stop rising, start to level off and might even decline.
Similar “late-age mortality plateaux” have been found in insects, and hinted at in rodents, but the discovery of one in humans will excite controversy.
If people essentially stop ageing after becoming centenarians, it is legitimate to ask: are there any natural limits to human lifespan?
This latest analysis was led by demographer Elisabetta Barbi, who scrutinised the hazard rates (measuring the likelihood of death) of all Italians aged 105 and above, who were living between 2009 and 2015. More than 3,800 Italians fell into this age group.
Bureaucratic pedantry was key: elderly people commonly report themselves older than they actually are, so Barbi’s team obtained birth and death records of age and survival. Similar records for Italians aged under 105 were gathered from a mortality database.
They reported their results in the journal Science last week: “By using clean data from a single nation we have shown that death rates, which increase exponentially up to about age 80, do decelerate thereafter and reach or closely approach a plateau after age 105.”
You are as likely to die at 110 as you are at 105 — although, at 50% every year the chances are still high.
The finding rekindles debate about whether there is a fixed maximum human lifespan.
The documented rise of the supercentenarian — those aged 110 and over — has also prompted renewed thinking on the subject. It is difficult to obtain precise numbers on these exceptionally long-lived individuals, but the US-based Gerontology Research Group lists 35 certified supercentenarians as of June. Two are men. Fourteen live in Japan, including the oldest person currently alive, a 117-year-old woman. Frenchwoman Jeanne Calment remains the world’s longestlived person: she died in 1997 aged 122.
The true number of supercentenarians worldwide is thought to be in the hundreds, but many are excluded from study because they lack supporting documentation. One problem with official dates is that sometimes only the last two digits of a year are recorded; until recently, the lives of some supercentenarians had straddled three centuries.
Evolutionary theory does, in fact, predict a levelling-off of death rates. If individuals vary in their genetic fitness and ability to survive environmental pitfalls, then the less robust are likely to die off first.
The genetically blessed, by virtue of their continued survival, define the surprisingly low death rate of their advanced age group.
And supercentenarians are nothing if not clinical outliers. They somehow dodge the usual slings and arrows of ageing and squeeze their decline into a short period right at the end of their lives, often dying of organ failure.
A pioneering 2006 study of 32 supercentenarians, published in the Journal of the American Geriatrics Society, found them to be virtually immune to vascular disease. Diabetes and Parkinson’s disease were rare, but cataracts and osteoporosis were common. About 40% were still functionally independent.
The documented numbers of supercentenarians needs to rise — and care of the elderly improve — before science can pronounce further on the natural limits of human lifespan.
More intriguing is that these (overwhelmingly female) warriors against ageing may harbour genetic and environmental clues to defying the horrors — heart disease, stroke and diabetes — that too swiftly claim the rest of us. /©
SIMILAR ‘LATE-AGE MORTALITY PLATEAUX’ HAVE BEEN FOUND IN INSECTS AND HINTED AT IN RODENTS