How long can a human hope to live, realistically? The recognised record is held by Jeanne Calment of France, who was 122 years and 164 days old when she died in 1997. How likely is it that someone will break her 24-year-old record, and, if so, when?
It is nearly 100% likely that someone will have lived beyond 122 by the end of the century, researchers have projected in a statistical study. Another study, this one based on biology and a novel index, has projected that it is possible for a human to live even to the age of even 150 — if other things go right.
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Between 122 and 135
The more recent one of the two studies, published on June 30 in the journal Demographic Research, uses statistical modelling to examine the extremes of human life in 13 countries. It was conducted by doctoral student Michael Pearce and Professor Adrian Raftery of the University of Washington. Their projections for maximum reported age at death for the period 2020-2100:
122 years: Near 100% probability that the current record will be broken.
124 years: Very likely, at 99%. Even for 127 years, the probability is as high as 68%.
130 years: Much less likely, at 13%.
Between 120 and 150
The other study, published on May 24 in Nature Communications, innovates a measure for people’s resilience — their ability to recover from stresses such as not getting enough sleep, strenuous exercises, or falling ill. It was conducted by a research team of Gero, a Singapore-based biotech company, in collaboration with Roswell Park Comprehensive Cancer Center in Buffalo, NY.
Led by Tim Pyrkov of Gero, they measured the resilience of study subjects over time, extrapolated their measurements, and found a complete loss of human body resilience at some age around 120-150 years.
“We found the trend of declining resilience with age. When projected to older ages, we observed that resilience is predicted to disappear, thereby suggesting the maximum lifespan,” Pyrkov told The Indian Express in an email.
Resilience was measured with an index called DOSI. Pyrkov described it as a biological age measure based only on the most affordable blood test — complete blood counts. “The main idea was that it would be easier to obtain repeated samples from the same individual,” he said.
Measuring longevity
The number of people surviving until 100 has been rising over the years, but the number of supercentenarians — those who cross 110 — remains relatively low. To calculate what the longest individual human lifespan could be by the year 2100, the University of Washington’s Pearce and Raftery used a common tool called Bayesian statistics.
“We use the UN’s method for predicting future life expectancy and mortality, which was actually developed by our group. This [takes] account of the past and current rate of improvement in each country,” Raftery said, by email.
The researchers made their projections from the International Database on Longevity, created by the Max Planck Institute for Demographic Research, which tracks supercentenarians from 10 European countries, and Canada, Japan and the US.
After reaching 110
While people are living longer, their chances of survival tend to flatten out after a point. Someone who is 110 has as much of a chance of surviving one more year as, say, someone who is 114. So, what is there to stop someone aged 127 from surviving the next year, and the next, until they reach 135?
“Nothing,” said Raftery. “The chance of surviving from age 110 to 111 is about ½. Same for the probability of a person aged 127 surviving to age 128… The chance of surviving 20 years, for example from age 110 to 130, is ½ to the power 20, which is about one in a million. The probability of surviving to age 135 is ½ to the power 25, which is about one in 32 million. The number of people reaching 110 in the first place will be far lower than that, so the probability of even one of them reaching 135 is very low,” he explained.
“But it is still possible, even if the probability is low.”
Why 150, or why not
If the Gero-led study projects a much higher maximum lifespan, the reason is not only the a different methodology, but also that it is for individuals without any major illness. What it means is that even if someone has no illness, their resilience will inevitably decline with age.
“… Once a therapy to extend resilience would be found, we might witness the extension of human life expectancy,” Pyrkov said.
Malina Bhattacherjee, then 100, being taken to a polling station in Kolkata in 2016. While more and more people are reaching the age of 100, people over 110 are still rare. (Express Archive) 
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