There is no limit to longevity, says study re-launching debate on human lifespan

There could be no natural limit to the life span of humans – at least not yet in view – contrary to the claims of some demographers and biologists

according to a statistical badysis published on Thursday in Science on the probabilities of survival of nearly 4000 "super-elderly" people in Italy, all aged 105 and over

A team led by the demographer Elisabetta Barbi of the Sapienza University and the statistician of Roma Roma University Francesco Lagona, found that the risk of death – which, throughout life, seems to increase as people get older – stabilizes after the age of 105, creating a "mortality plateau". At this point, researchers say that the chances of dying from one birthday to the next are about 50:50 (see "Unlimited Longevity").

"If there is a mortality plateau, then there is no limit to humans. Longevity, "says Jean-Marie Robine, demographer at the French Institute of Health and Medical Research Montpellier, who did not participate in the study.

That would mean that someone like Chiyo Miyako, the great-great-grandmother who, at age 117, is the oldest known person in the world, could live for years to come – or even forever, at least hypothetically.

Researchers have long wondered if humans have a higher age limit. The consensus is that the risk of death increases steadily in adulthood, up to about 80 years or more. But there is a vehement disagreement about what happens when people get into their 90s and 100s.

Some scientists have looked at the demographics and concluded that there is a fixed and natural "shelf life" for our species and mortality rates increase. Others have looked at the same data and concluded that the risk of death flattens in its ultra-golden years, and therefore that the human life span has no upper threshold.

Age of Rage

In 2016, geneticist Jan Vijg and his colleagues from the Albert Einstein College of Medicine in New York revived the debate by badyzing the ages of the oldest people in the world for the most from half a century. They estimated that human longevity peaked at about 115 years – 125.

Vijg and his team argued2 that with little to no lifetime gains since the mid-1990s, human aging had reached its natural limit. The longest known life belongs to Jeanne Calment, a French super-centenarian who died in 1997 at the age of 122.

The experts challenged the statistical methods of the 2016 study, triggering a Fire storm now Barbi and Lagona. In collaboration with colleagues from the Italian National Institute of Statistics, the researchers collected data on all Italians aged 105 years and over between 2009 and 2015, collecting death, birth and survival certificates in order to minimize the risks of exaggeration.

They also tracked individual survival trajectories from one year to the next, rather than grouping individuals into age brackets, as did previous studies combining datasets. And by focusing solely on Italy, which has one of the highest rates of per capita per capita in the world, they have avoided the issue of variation in data collection between different jurisdictions.

at the Oxford Institute of Population Aging in the United Kingdom, "these data provide the best evidence to date of extreme mortality plateaus in humans."

Ken Wachter, a mathematical demographer at the # 39, University of California, Berkeley, and one author of the latest study, suspect that earlier disputes over trends in late mortality largely stem from poor records and statistics. "We have the benefit of better data," he says. "If we can get data of this quality for other countries, I think we will see the same thing."

Robine is not so sure. He says unpublished data from France, Japan and Canada suggest that evidence of a mortality plateau "is not so clear". An overall badysis is still needed to determine whether discoveries in Italy reflect a universal hallmark of human aging, he says.

Out of bounds

The world has about 500,000 people over the age of 100, a figure that is expected to nearly double with every decade to come. Even though the risk of late mortality remains constant at 50:50, the increase in the number of club members by more than 100 people should translate into an upward shift in the older person of around one year per decade, according to Joop de Beer, researcher on longevity at the Dutch Interdisciplinary Demographic Institute in The Hague

Many researchers hope to better understand what lies behind the leveling of mortality rates more late in life. Siegfried Hekimi, a geneticist from McGill University in Montreal, Canada, speculates that the body's cells eventually reach a point where repair mechanisms can compensate for other damage to keep the death rate at one level.

. I think we have no idea, Hekimi says.

For James Kirkland, a geriatrician at the Mayo Clinic in Rochester, Minnesota, solid evidence of a mortality plateau indicates that it is possible to prevent death at any age. Some experts think that the very fragile are irreparable. But if the chances of dying do not increase over time, he says, interventions that slow down aging are likely to make a difference, even in very old people.

Not everyone buys this argument or the conclusions of the last article.

Brandon Milholland, co-author of the 2016 article Nature claims that evidence of a mortality plateau is "marginal", the study including less than 100 people who have lived up to 110 years or more. Leonid Gavrilov, a researcher on longevity at the University of Chicago in Illinois, notes that even small inaccuracies in the records of Italian longevity could lead to a fallacious conclusion.

Others say that the findings of the study are biologically improbable. Jay Olshansky, a bio-demographer at the University of Illinois at Chicago, notes that cells that do not replicate, such as neurons, will continue to wither and die as the person ages. According to Haim Cohen, a molecular biologist at Bar-Ilan University in Ramat-Gan, Israel, this study should therefore not be the last word on the age-limit dispute. "I'm sure the debate will continue."

This article is reproduced with permission and was published on June 28, 2018.