For most of the 20th century, life expectancy in developed countries increased by about three years for every ten consecutive years. For people born at the turn of the 21st century, these increases mean that they live an average of 30 years longer than those born in 1900, and can live to be 80 years old.
This phenomenon is called "radical life extension" and is a gift given to mankind by the advancement of various medical technologies and public health measures. Many scientists and ordinary people believe that this trend will continue and human life span will be extended indefinitely at the same rate. Others, however, predict that humanity will hit a natural ceiling, with life expectancy in the world's longest-lived countries peaking before 100 years old.
The latest research on this hotly debated issue suggests that humans have actually reached the upper limit of their lifespan. Despite advances in medical technology designed to extend lifespan, the findings show that the average rate of improvement in life expectancy has slowed over the past three decades in the countries with the longest lifespans.
That's because efforts to slow aging -- a poorly understood set of biological processes whose effects include frailty, dementia, heart disease and sensory impairments -- have so far been unsuccessful, said S. Jay Olshansky, a professor of public health at the University of Illinois at Chicago and lead author of the new study published in Nature Aging. "When you push the body beyond the warranty period, our bodies don't function very well."
"As people live longer, it's like playing whack-a-mole," he added. "Each mole represents a different disease. The longer a person lives, the more moles appear and the faster they appear."
In 1990, Olshansky published a paper in Science predicting that the growth rate of human life expectancy would slow down even as medical progress accelerated. He concluded at the time that it was "extremely unlikely" that the average human life span would exceed 85 years.
He said the paper had been met with widespread opposition because of "a vested interest in the idea that life expectancy continues to increase".
Still, Olsonsky was convinced he was right. So he decided to "be a patient scientist" and retest his hypothesis once real-world data became available. He added that it had taken 34 years, but the wait had finally paid off, with "a clear yes" supporting his initial findings.
Olsensky and his colleagues took a simple and straightforward approach: They looked at how mortality and life expectancy changed from 1990 to 2019 in eight of the world's longest-lived countries - Japan, South Korea, Australia, France, Italy, Switzerland, Sweden and Spain - as well as the United States and Hong Kong. They found that improvements in life expectancy slowed in nearly all of those places, while life expectancy in the United States actually declined.
South Korea and Hong Kong are exceptions. Olsonsky said the recent acceleration in survival rates in these two places, which researchers suspect is related to the fact that life expectancy in these two places has only increased significantly in the last 25 years. Even so, in Hong Kong - which has the longest-lived population in the world - researchers found that only 12.8% of women and 4.4% of men born in 2019 were expected to live to 100.
The numbers are much lower in the United States, where only 3.1% of female children and 1.3% of male children are expected to live to age 100.
To put their findings into perspective, Olshansky and his colleagues also calculated what life expectancy would look like if humans did keep up with radical life extension. For example, if this were the case, 6% of Japanese women would live to be 150, and about one in five Japanese women would live past 120. "We don't call these situations 'absurd' in the paper, but we hope people will be able to draw such conclusions on their own," Olsonsky said.
The new paper's methods and conclusions "make perfect sense," said Jan Vijg, a biologist and geneticist at the Albert Einstein College of Medicine who was not involved in the study. "There is really no evidence that living to 100 will become a reality anytime soon."
Wieger added that the new paper's findings mirror some previous research, including one he and his colleagues published in 2016, which reached the same conclusion about lifespan limits. "After our paper was published, there was an overwhelming response from both the scientific and non-scientific communities, saying that we were charlatans, that our data were flawed, that there was no evidence that there was a lifespan limit. Needless to say, our data were never found to be flawed," Weig said.
Despite the weight of the new evidence, Olshansky fully expects his and his colleagues' findings to be controversial.
But he believes scientists should turn their attention away from the "untested hypothesis" of continuing aggressive life extension and instead turn to "earth science" - a relatively new field of research that focuses on extending people's "healthspan", which is the number of healthy years that people can enjoy, rather than their overall lifespan. Olsonsky and his colleagues wrote in the new paper that unless new technologies address the problem of aging, further radical extension of lifespan in already long-lived countries "remains impossible."
Nalini Raghavachari, a program officer at the National Institute on Aging who was not involved in the study, also believes that the focus of research should be on understanding and achieving healthy aging. Clues on how to do this may come from some of the world's longest-lived people, she said. Raghavachari added: "A deeper understanding of the protective effects and mechanisms behind exceptional healthspan could lead to the development of new therapeutic targets and interventions to promote healthy aging."