Whether there is actually a limit to the human lifespan is the question that is being pursued by modern antiaging researchers and longevity experts. However, that question has been fiercely debated for centuries.
It’s a question with importance beyond just who gets to lay claim to being the “oldest living person recognized by Guinness World Records. Because determining whether human lifetimes have an inviolate maximum might offer clues to understanding aging, as well as aiding research on prolonging life.
“The possible existence of a hard upper limit, a cap, on human lifetimes is hotly debated,” writes Léo Belzile and coauthors in a paper soon to appear in the Annual Review of Statistics and Its Application. “There remains a sustained and widespread interest in understanding the limit, if there is any, to the human life span.”
The author’s reanalysis of data on extreme lifetimes indicates that any longevity cap would be at least 130 years and possibly exceed 180. And some datasets, the authors report, “put no limit on the human life span.”
These analyses by Belzile and his colleagues “suggest that the human life span lies well beyond any individual lifetime yet observed or that could be observed in the absence of major medical advances.”
One of the big problems of using historical longevity data to determine if there is an upper limit on human lifespan is the inherent inaccuracy of such data, especially when taking into account claims of extreme lifespan that occurred prior to the turn of the 20th Century.
Yet, even today, say the authors of the study, the lack of high-quality data confounds statistical attempts to estimate a maximum life span. “Age overstatement is all too frequent, as a very long life is highly respected, so data on supercentenarians must be carefully and individually validated to ascertain that the reported age at death is correct,” write Belzile and coauthors.
Fortunately, some collections provide verified data on the oldest of the old. One such collection, the International Data Base on Longevity, includes information from 13 countries on supercentenarians (those living to age 110 or beyond) and for ten countries on semi-super centenarians (those reaching 105 but not making it to 110).
The Force of Mortality
Analyzing such datasets requires the skillful use of multiple statistical tools to infer maximum longevity. A key concept in that regard is called the “force of mortality,” or “hazard function,” a measure of how likely someone reaching a given age is to live a year longer. (A 70-year-old American male, for instance, has about a 2 percent chance of dying before reaching 71.)
Of course, the hazard of dying changes over time — a youngster is generally much more likely to live another year than a centenarian is, for instance. By establishing how death rates change with age, statistical methods can then be applied to estimate the maximum possible life span.
Applying the “force of mortality” estimate to the semi-super centenarians and super-centenarians analyses of those groups suggest that by age 110 or so, the rate of dying in each succeeding year is roughly 50 percent — and the data so far does not rule out an even smaller annual chance of death after that.
According to the paper, depending on the details of the dataset, a possible longevity cap is estimated in the range of 130–180. But in some cases, the statistics imply a cap of at least 130, with no upper limit.
Mathematically – at least – that implies that the highest ages in a big enough population could be infinite — implying immortality.
However, ruling out some modern-day antiaging breakthrough, the authors say statistical analysis is one thing, but in reality, there’s almost no chance that anybody will beat Methuselah’s Biblical old age record of 969. The lack of a mathematical upper bound does not actually allow a potentially infinite lifespan – for now.
“Every observed lifetime has been and always will be finite,” Belzile and coauthors write, “so careful translation of mathematical truths into everyday language is required.”