Life expectancy is increasing at a slower rate this century — and it may be because we're reaching our human limit

Human life expectancy is increasing at a slower rate than it did in the 20th century, a new study of 10 wealthy countries hints.

During the 20th century, improvements in public health and medicine resulted in "radical life extension": With each passing decade, the average life expectancy at birth in some of the world's longest-lived populations in high-income countries increased by around three years. These increases in life expectancy were initially driven by reductions in the death rates of children, followed by declines in the death rates of middle-aged and older people. For instance, in the U.S. in 1900, the average life expectancy at birth was 47.3; by 2000, it had increased to 76.8.

But now, a new paper suggests that a similar explosion in life expectancy won't occur in the 21st century.

The report, published Monday (Oct. 7) in the journal Nature Aging, predicts that people can only be expected to gain an extra 2.5 years over the next three decades.

Related: COVID pandemic knocked 1.6 years off global life expectancy, study finds

The most likely explanation for this deceleration is that humanity is now approaching the upper limit of its life expectancy, the authors of the study argue. In other words, with more people surviving to older ages, the main risk factors for death are related to biological aging — the gradual accumulation of damage to cells and tissues that inevitably occurs over time. We know how to prevent children from dying of measles, but we can't yet stop the biological clock that keeps ticking once that child reaches age 60, 70 and beyond.

Tackling one age-related disease at a time — for instance, by trying to develop cures for Alzheimer's disease or cancer — is like putting on a "temporary survival Band-Aid," said Jay Olshansky, lead study author and a professor of epidemiology and biostatistics at the University of Illinois Chicago. These efforts to develop better treatments — and, eventually, cures — can enable people to live long enough to experience aging, but they don't tackle the root issue of aging, he told Live Science.

In their new study, Olshansky and colleagues investigated trends in life expectancy between 1990 and 2019. They analyzed national vital statistics data from nine regions with the longest-lived populations — Australia, France, Italy, Japan, South Korea, Spain, Sweden, Switzerland and Hong Kong. They also looked at figures from the U.S., as some scientists made specific predictions about radical life extension in the country, they wrote in the paper. The researchers then used this retroactive analysis to predict future trends in life expectancy that may occur this century.

The team found that overall improvements in life expectancy decelerated across these 10 countries, particularly after 2010. Current birth cohorts have a small likelihood of making it to 100 — females have a 5.1% chance, and males have a 1.8% chance.

Of children born in 2019, those from Hong Kong were most likely to reach 100, with females having a 12.8% chance and males having a 4.4% chance.

These findings suggest that, to continue extending human life expectancy, more research should be channeled into the study of geroscience, which investigates the biology of aging, rather than just the diseases associated with the process, Olshansky said. In this context, it is important to note that life expectancy is different to life span, which defines the maximum age to which any human has ever lived.

Investigating ways to slow or reverse cellular aging could help people remain "younger" for longer, Olshansky suggested. For instance, scientists are developing drugs that may be able to slow aging by extending caps at the end of chromosomes, known as telomeres, which normally dwindle over time.

"Now, we need to focus on manufacturing the most precious commodity on Earth, which is healthy life," he told Live Science.

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