Have we pushed the limits of human lifespan?

New medicines, better understanding of the importance of sound nutrition and exercise and other wellness-related improvements have all contributed to letting more people live longer, but the fountain of youth remains elusive. And new research suggests that we’ve probably reached or are at least close to the biological limits of the human lifespan.

Published in the journal Nature Aging, the study “Implausibility of Radical Life Extension in Humans in the 21st Century” finds evidence that humans are approaching what researchers call a “biologically based limit to life.” We’ve already gained years by conquering some major diseases, which provided significant stretching of longevity, S. Jay Olshansky, of the University of Illinois Chicago School of Public Health, said in a news release.

But damage due to aging can’t be conquered the same way, so it provides what Olshansky calls the main obstacle to further longevity gains.

“Despite frequent breakthroughs in medicine and public health, life expectancy at birth in the world’s longest-living populations has increased only an average of six and a half years since 1990,” the study found. As noted in the release, “That rate of improvement falls far short of some scientists’ expectations that life expectancy would increase at an accelerated pace in this century and that most people born today will live past 100 years.”

He noted that “most people alive today at older ages are living on time that was manufactured by medicine. But these medical Band-Aids are producing fewer years of life even though they’re occurring at an accelerated pace, implying that the period of rapid increases in life expectancy is now documented to be over.”

What is life expectancy?

Life expectancy estimates are an average of how long a baby born in a given year might live, if existing death rates remain the same throughout that lifetime. As The Associated Press noted, “It is one of the world’s most important health measures, but it is also imperfect: It is a snapshot estimate that cannot account for deadly pandemics, miracle cures or other unforeseen developments that might kill or save millions of people.”

The researchers analyzed life expectancy estimates from 1990 to 2019, using data from the Max Planck Institute for Demographic Research. They looked at eight countries where people live a long time: Australia, France, Hong Kong, Italy, Japan, South Korea, Spain and Switzerland. And they added the U.S. because it’s home and due to earlier predictions of a surge in lifespan that have yet to materialize. The U.S. doesn’t rank in the top 40 countries for long life.

Olshansky told The New York Times that he expects maximum life expectancy to end up around 87 years: roughly 84 for men and 90 for women. And he noted that some countries already come close to that.

But extending life expectancy further through medical advances like disease reduction is unlikely to be good news unless the years added are healthy years. Research suggests longevity gains will continue to slow as people encounter effects of aging that cannot be changed. “We should now shift our focus to efforts that slow aging and extend healthspan,” he said.

Some will continue to reach their 100th year and perhaps beyond, but that won’t be a common story enjoyed by most people, per the research, though the study authors don’t rule out potential improvements.

“This is a glass ceiling, not a brick wall,” Olshansky said. “There’s plenty of room for improvement: for reducing risk factors, working to eliminate disparities and encouraging people to adopt healthier lifestyles — all of which can enable people to live longer and healthier. We can push through this glass health and longevity ceiling with geroscience and efforts to slow the effects of aging.”

Even getting rid of deaths before age 50 would not make significant differences, since aging itself ultimately ends in death. The study said that reducing those early deaths to zero adds 1 year to the life expectancy for women and 1.5 to that of men.

Built to last?

Two decades ago, Olshansky and two friends — Bruce A. Carnes and Robert N. Butler — who also study aging were contemplating what people would look like if they were designed with longevity in mind. Olshansky described a “muscular elf” with big, mobile ears, knees that bent the other way to minimize grinding and other “innovations,” as reported by Deseret News . Their design was published in Scientific American and updated a decade later.

Of the human body, the trio wrote: “The living machines we call our bodies deteriorate because they were not designed for extended operation and because we now push them to function long past their warranty period. The human body is artistically beautiful and worthy of all the wonder and amazement it evokes. But from an engineer’s perspective, it is a complex network of bones, muscles, tendons, valves and joints that are directly analogous to the fallible pulleys, pumps, levers and hinges in machines. As we plunge further into our postreproductive years, our joints and other anatomical features that serve us well or cause no problems at younger ages reveal their imperfections. They wear out or otherwise contribute to the health problems that become common in the later years.”

The new study also included researchers from University of Hawaii, Harvard and UCLA.