Humans have long been fascinated with maximizing human lifespan, possibly driven by a universal desire for more time. Average life expectancy at birth dramatically increased in the 20th century, due to improved sanitation, reduced infant mortality, reduced infectious mortality thanks to antibiotics, and preventative treatment of cardiovascular disease. But will the trajectory of rapid lifespan extension continue? A recent study examined the trends in mortality rates from the last three decades to determine if the projected average lifespan at birth is expected to keep increasing at rapid rates in the already longest-lived countries.1
Measuring changes in expected lifespan at birth
At the beginning of the 20th century in the United States, life expectancy at birth was about 47 years, whereas by midcentury, life expectancy increased to around 66 years for men and 71 years for women. Life expectancy increased to about 78 years by the end of the century. This 66% increase in life expectancy works out to a yearly average increase of about 0.33 years, the current standard for what is considered radical life extension (a yearly increase of 0.3 years, or 3 years per decade).
In the present study, investigators Olshansky and colleagues used the annual age-specific and sex-specific death rates and period life expectancy at birth from 1990–2019 derived from the Human Mortality Database to assess whether the trend of radical life extension has continued in the past three decades. They used information from the eight countries with the longest-lived populations to evaluate trends in life expectancy and the effects of hypothetical reductions in mortality. Also included in the analysis were Hong Kong, a more recent area with a longer-living population, and the United States, which is sadly not among the top countries for life expectancy, but serves as an important comparison. (The U.S., despite its status as a very wealthy nation, saw rising mortality of its middle-age population between 2010 to 2019 and currently has an approximately 8-year lower life expectancy at birth than the longest-lived populations.)
What the study found
The study found that the annual rise in life expectancy has largely slowed over the past thirty years. The defined 0.3-year annual or 3-year-per-decade improvement in life expectancy was only observed in South Korea from 2010 to 2019 and from 1990 to 2000 in Hong Kong. In most of the observed populations, the most recent decade (2010-2019) had a decelerating annual rise in life expectancy at birth, dropping to below 0.2 years annually for eight of the ten populations. Additionally, most of the included countries only increased in survivorship to 100 years of age by 1-2% over the three-decade period, with slightly higher increases in Japan and Hong Kong, approximately 4 and 6%, respectively. However, none of these trends, even if they continued at the same rate, would lead to a 50% or greater survivorship to 100 by the turn of the next century.
The natural follow-up is to determine what magnitude of changes would need to occur to keep raising life expectancy. In all ten included countries, life expectancy has increased since 1990, yet the study estimated that even if deaths of people younger than 50 were completely prevented going forward, average life expectancy at birth would only rise by 1–1.5 years, indicating that the greatest impact on life expectancy at present is not the loss of young lives.
Indeed, to keep increasing life expectancy, all-cause mortality (ACM) would have to be reduced at all ages by a greater percentage now than was required to create the same incremental rise thirty years ago. For instance, in current-day Japanese men, a 9.5% reduction in ACM at all ages would be required to raise life expectancy from 82 to 83 years, while a one-year extension in life expectancy of Japanese women, who on average live longer than Japanese men, would require an even larger reduction in ACM – a whopping 20.3% in all ages to raise life expectancy from 88 to 89 years. As these data suggest, as average life expectancy increases, each additional one-year increase requires a greater reduction in mortality, making it more difficult to maintain the standard for radical life extension in the longest-lived nations. This is potentially an explanation for the observed deceleration in life expectancy trends.
What does this mean?
The timing of the 20th-century improvements in life expectancy varied across the ten included populations, which suggests that the life extension thus far has been largely due to better living conditions and the elimination or treatment of disease – processes which would occur in different nations on different timelines. For instance, the radical rise in life expectancy in Hong Kong during the 1990s is attributed to economic prosperity and tobacco control in that country. Japan also had a later increase in life expectancy in the last third of the 20th century, attributed to economic prosperity and advancements in medical technology, which led to large reductions in infant mortality, reduced cerebrovascular deaths from public health initiatives to lower blood pressure, and more widespread healthcare after they adopted a national healthcare system in 1961.
But all of these improvements came from improving survivorship at all ages by reducing disease-associated mortality, not by altering aging-associated mortality – a critical distinction as humanity reaches ever more advanced average life expectancies. To illustrate the difference, consider the analogy of an oak tree: reducing disease-related mortality in an oak tree might involve improvements in soil nutrition and protection from acute events like fires, lightning strikes, and pest infestations. But even with the best protection, an aged oak tree will eventually decline in health due to accumulated stress, reduced wound healing, and less resiliency to normal environmental stressors like droughts or periods of high rainfall. In all likelihood, there is an upper limit to lifespan in all living beings that is determined by the biology of aging itself.
Olshansky et al.’s data provide further evidence that we, as humans, are asymptotically approaching that limit. They show that although life expectancy increased, maximum lifespan has stagnated, and lifespan variation declined. Together this means that even though life expectancy is longer, the age at death has been compressed into a shorter window of time – in essence, we’re all crowding closer to the limit, but the limit itself hasn’t budged. Consider this hypothetical situation posed by the study authors as to why current trends are unlikely to continuously raise life expectancy: radical life extension for Japanese females (an increase of 0.3 years for the next 75 years) would result in a 22.5-year increase in life expectancy, leading to an average age of mortality of 110 years. However, this would require that 70% of females live to be 100 and 6% of females live to be 150, nearly thirty years longer than the longest-lived person ever on record!
There is no evidence to suggest that humans can live to 150 years of age without sophisticated interventions that challenge the very fundamentals of aging biology, and some models suggest that there is less than a one in 10,000 chance of even living beyond 125 years in any given year.2 However, all of the models and projections are rooted in the fact that there are no human interventions to date that slow the biological process of aging and assume that accumulation of cellular damage is inevitable, leading to declining organ function and eventually organ system failure.
The final word on radical lifespan extension?
While this study demonstrated that there is a limit to the extension of lifespan by preventing or treating chronic disease via current treatments and their (late) applications, a major limitation of this study is that it cannot predict future advances in medicine or aging biology that would have step-function-like impacts on lifespan (a limitation acknowledged by the authors).
A jump in human lifespan could be driven by a single breakthrough or a combination of discoveries in different fields, including geroprotective drugs, genetic engineering, and human-machine interfacing. Geroprotective drugs like rapamycin have demonstrated in the Interventions Testing Program (ITP) an increase in the total lifespan of the longest-lived mice by 9-14% as well as an overall increase in median survival.3 While that bump in lifespan alone might not be enough to help a human live beyond 125 years, proof-of-concept studies in genetic engineering have demonstrated significant increases in lifespan in simple organisms, such as yeast and worms. Although humans are far more complex creatures, it is not unreasonable to think that it may become possible this century to slow aging through genetic manipulations of specific tissues.
More broadly, even the way we think about lifespan may change in the coming decades. With more developments in artificial brains, machine-brain interfaces, and artificial intelligence, it may become possible to “download” our consciousness onto a computer. Right now we define human lifespan as the number of chronological years in one body, but leaps in technology might change how we even define human lifespan itself.
The bottom line
While it may seem like the study by Olshansky et al. squashes hope of living significantly longer, all this study tells us is that we are approaching the limits of lifespan set by aging biology – but if there has been any unifying theme across the history of our species, it’s that humans have a knack for overcoming limits. It certainly isn’t in our biology to fly, yet to most people reading this, spending a few hours cruising 30,000 feet above land is practically mundane. Even thirty years ago, we couldn’t have conceived of technology as it exists today. Imagine trying to describe a smartphone or generative AI to someone in 1990 – it would seem like science fiction.
Likewise, a few decades from now, there may be new therapies that can modulate the biological rate of aging in a way that helps us live much longer and better in ways we couldn’t fathom today. Though in the meantime, our best bet for reducing mortality risk is still exercising, eating well, being social, and getting good sleep, with the goal of staying as healthy for as long as possible within the current bounds of the aging human body.
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References
- Olshansky SJ, Willcox BJ, Demetrius L, Beltrán-Sánchez H. Implausibility of radical life extension in humans in the twenty-first century. Nat Aging. Published online October 7, 2024:1-8. doi:10.1038/s43587-024-00702-3
- Dong X, Milholland B, Vijg J. Evidence for a limit to human lifespan. Nature. 2016;538(7624):257-259. doi:10.1038/nature19793
- Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature. 2009;460(7253):392-395. doi:10.1038/nature08221
This article gives many people a good foundation and framework in which to explore their own longevity.