We’ve seen dramatic increases in life expectancy over the 19th and 20th centuries, thanks to healthier diets, medical advances and many other quality-of-life improvements.

But after nearly doubling over the course of the 20th century, the rate of increase has slowed considerably in the last three decades, according to a new study led by the University of Illinois Chicago.

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 analysis found. 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.

The Nature Aging paper, “Implausibility of Radical Life Extension in Humans in the 21st Century,” offers new evidence that humans are approaching a biologically based limit to life.

The biggest boosts to longevity have already occurred through successful efforts to combat disease, said lead author S. Jay Olshansky of the UIC School of Public Health. That leaves the damaging effects of aging as the main obstacle to further extension.

“Most people alive today at older ages are living on time that was manufactured by medicine,” said Olshansky, a professor of epidemiology and biostatistics. “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.”

That also means extending life expectancy even more by reducing disease could be harmful, if those additional years aren’t healthy years, Olshansky added. “We should now shift our focus to efforts that slow aging and extend healthspan,” he said. Healthspan is a relatively new metric that measures the number of years a person is healthy, not just alive.

The analysis, conducted with researchers from the University of Hawaii, Harvard and UCLA, is the latest chapter in a three-decade debate over the potential limits of human longevity.

In 1990, Olshansky published a paper in Science that argued humans were approaching a ceiling for life expectancy of around 85 years of age and that the most significant gains had already been made. Others predicted that advances in medicine and public health would accelerate 20th-century trends upward into the 21st century.

Thirty-four years later, the evidence reported in the 2024 Nature Aging The study supports the idea that life expectancy gains will continue to slow as more people become exposed to the detrimental and immutable effects of aging. The study looked at data from the eight longest-living countries and Hong Kong, as well as the United States—one of only a handful of countries that has seen a decrease in life expectancy in the period studied.

“Our result overturns the conventional wisdom that the natural longevity endowment for our species is somewhere on the horizon ahead of us—a life expectancy beyond where we are today,” Olshansky said.

“Instead, it’s behind us—somewhere in the 30- to 60-year range. We’ve now proven that modern medicine is yielding incrementally smaller improvements in longevity even though medical advances are occurring at breakneck speed.”

While more people may reach 100 years and beyond in this century, those cases will remain outliers that won’t move average life expectancy significantly higher, Olshansky said.

That conclusion pushes back against products and industries, such as insurance and wealth-management businesses, which increasingly make calculations based on assumptions that most people will live to be 100.

“This is profoundly bad advice because only a small percentage of the population will live that long in this century,” Olshansky said.

But the finding doesn’t rule out that medicine and science can produce further benefits, he said. There may be more immediate potential in improving quality of life at older ages instead of extending life, the authors argue. More investment should be made in geroscience—the biology of aging, which may hold the seeds of the next wave of health and life extension.

“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.”