Editor's note: This popular story from the Daily Briefing's archives was republished on Sept. 30, 2019.
In five rebuttal papers published in the journal Nature, researchers push back against a controversial study published in 2016 that argued the human lifespan caps at about 115.
Background: Have humans reached peak lifespan?
For the 2016 study, also published in the journal Nature, researchers analyzed decades of longevity records for 41 countries and territories stored in the Human Mortality Database to determine how fast the population grew at different age groups by comparing the numbers year to year.
They found that the oldest age reached in 1968 was 111. That increased to about 115 by the 1990s, the researchers said. And while the researchers acknowledged that there will always be some exceptions to the rule—Jeanne Calment, the human with the oldest recorded age, died in 1997 at age 122—they estimated the chances of someone living past age 125 in a given year is less than 1 in 10,000.
Lead study author Jan Vijg of the Albert Einstein College of Medicine concluded, "From now on, this is it. Humans will never get older than 115."
Critics beg to differ
But not everyone is convinced by Vijg's research, McClatchy reports. Nature—which faced criticism for publishing the original paper—recently published five rebuttals.
In one rebuttal, Siegfried Hekimi and colleagues at McGill University argued that while there may be a limit to the human lifespan, the available data do not support the conclusion that 115 is the peak.
For instance, the rebuttal said Vijg visually assessed the data, determined that there was a plateau in aging around 1995, and then divided the data into two time periods: before and after 1995. When Vijg then calculated the underlying trends for each time period, the post-1995 time period seemed to level off, which seemed to support Vijg's hypothesis. But Hekimi argued that such an approach to measuring data was inaccurate.
In fact, according to Hekimi, the data "are compatible with many different trajectories and not at all an ongoing plateau." For instance, Hekimi said in one scenario, the data might indicate that lifespans will continue to increase, so that by 2300, the oldest individual would be an estimated 150 years old. "By extending trend lines, we can show that maximum and average lifespans could continue to increase far into the foreseeable future," he said. "The increase in average lifespan will not suddenly crash into a 115-year limit."
In another rebuttal, Nick Brown, a PhD student at the University of Groningen, also outlined concerns with how Vijg first eyeballed a plateau in the data and then tested the same data set for confirmation. "Apparently, they thought they had found a pattern, then they develop a theory to explain the pattern," Brown said. "Then, presto, the data matches the theory—well of course, because the theory was generated from (that) data. That's a pretty fundamental bug in the way of doing science."
Brown also pointed out that Vijg's study included only the oldest person who died each year in the overall analysis of lifespans. According to Brown, that approach engendered a small sample size with an "awful lot of randomness."
The author of a third rebuttal—Maarten Pieter Rozing, a professor at the University of Copenhagen's Center for Healthy Aging—also voiced concern about the original study's focus on only the oldest people to die each year. "The available data are limited, there aren't that many supercentenarians," Rozing said. "And I think there are no strong arguments that show there is a decline. (Instead), I think all evidence points towards an increase—we can just wait and see who's right."
According to The Scientist, the remaining two rebuttals echoed the concerns outlined in the first three. James Vaupel—a specialist in aging at the Max Planck Institute for Demographic Research in Germany and co-author of the fifth rebuttal—concluded, "The evidence points towards no looming limit ... At present the balance of the evidence suggests that if there is a limit it is above 120, perhaps much above—and perhaps there is not a limit at all."
Researcher disputes critics
For his part, Vijg said he accepts "absolutely nothing" in the latest criticisms. He contends that the critics are engaging in statistical nitpicking and "hadn't read his paper properly."
For instance, citing the argument in several rebuttals that Vijg's team based his hypothesis on a dataset and then used that same dataset to test the hypothesis, Vijg said his study actually looked at two separate databases. "One top of that, it's well known in statistics that you are allowed to look at the data," he said. "For quite a while, statisticians didn't want you to do that because they thought it was not objective. But that changed decades ago when people realized that you should look at the data, make inferences, and apply the right statistical test."
Further, Vijg suggested the critics, to a degree, are upset at being confronted with their own mortality.
And Jay Olshansky—a professor of public health at the University of Illinois at Chicago, who was not involved in Vijg's study—said the rebuttals do not debunk the claim that the human lifespan is inherently limited. "The very phenomenon that they see, which is a very small number of old people, is a result of a limit to the duration of life," Olshansky said.
Olshansky argued that the primary takeaway of the dispute is that human beings will eventually die, even if medical interventions extend the average lifespan. "It doesn't matter if (the age limit) is 115, 118, or 120," he said. "The most important message to get across, in my view, is that we should not be trying to make ourselves live longer, we should only be trying to extend the period of healthy life" (Hadley, McClatchy/Sacramento Bee, 6/28; Rossman, USA Today, 6/28; Devlin, The Guardian, 6/28; Kwon, The Scientist, 6/28).
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