why discovery took 30 years to prove

Put aside the hype about the growing number of us who are likely to make it to 100, because the rise in human life expectancy might actually be slowing down. At least, according to a study that analysed mortality data for ten countries or regions over the past three decades¹.

“There are limits to how far out we can push out the envelope of human survival,” says study co-author S. Jay Olshansky, an epidemiologist at the University of Illinois Chicago. “If you live long enough, you run up against the biological process of ageing.”

The era of what he calls radical life extension is over, he argues. Some researchers, however, disagree and point out that medical science could yet find a way to push age limits.

Advances in public health and medicine during the twentieth century increased human life expectancy to about three years per decade. But Olshansky and others have long argued that this rate of improvement is not sustainable, despite more-optimistic forecasts that predict most children born in the twenty-first century would live for a 100 years or more². But this is difficult to confirm, because the only way to be sure is to wait for enough people to die, or not.

With his colleagues, Olshansky first published the idea³ that human life expectancy has a finite limit in 1990. “We have waited 30 years to test this,” he says. “And we now have definitive evidence that the limited lifespan hypothesis is correct.”

That evidence is based on the numbers of reported deaths in parts of the world with some of the highest current life expectancies, including Hong Kong, Japan, South Korea, Australia, France, Italy, Switzerland, Sweden, the United States and Spain. The analysis looked at the period of 1990 to 2019, to avoid the distorting impact of the COVID-19 pandemic.

The team found that the rate of improvement in life expectancy in the decade of 2010–19 had dropped below that seen between 1990 and 2000. People were still living longer, but not by as much. In fact, in every population except those of Hong Kong and South Korea, the decadal rise in life expectancy decelerated to below two years.

Overall, the study found that children born since 2010 have a relatively small chance of living to 100 (5.1% chance for women and 1.8% chance for men). The most likely cohort to see a full century are women in Hong Kong, with a 12.8% chance.

Can we overcome ageing?

It’s clear that further extension of the average lifespan is difficult because that would require researchers to find treatments for illnesses that affect older people, says Dmitri Jdanov, a demographer at the Max Planck Institute for Demographic Research in Rostock, Germany. Jdanov wrote, together with his colleague Domantas Jasilionis, an accompanying commentary on the paper. Both articles are published in Nature Aging today.

But Jdanov thinks that Olshansky is too pessimistic about possible progress. “Although making another leap might be difficult, the rapid development of new technologies may lead to an unexpected health revolution,” he says.

A century ago, few researchers would have thought that child mortality could be reduced considerably, he says. But advances in vaccines, education and public health have since slashed the rate from more than 20% in 1950 to less than 4% now.

“If we cannot imagine something, it doesn’t mean that it’s impossible,” Jdanov says.

The study also revealed what Olshansky calls a “shocking” decline in the average life expectancy in the United States in the decade starting in 2010 — a trend seen in such a long-lived population only after extreme events, such as war, since 1900. The decline in the United States is driven by increasing numbers of deaths because of conditions such as diabetes and heart disease in people aged roughly 40 to 60.

“It tells you that something pretty negative is happening among some subgroups of the population to drag the average down, because the wealthier, more highly educated subgroups are actually doing better,” Olshansky says.