“In 1990, it was hypothesized that humanity was approaching an upper limit to life expectancy (the limited lifespan hypothesis) in long-lived populations, as early gains from improved public health and medical care had largely been accomplished, leaving biological aging as the primary risk factor for disease and death; the rate of improvement in life expectancy was projected to decelerate in the twenty-first century; and e(0) [life expectancy at birth] for national populations would not likely exceed approximately 85 years (88 for females and 82 for males) unless an intervention in biological aging was discovered, tested for safety and efficacy and broadly distributed. These conclusions were later supported by observed mortality dynamics in the United States, France and Japan from 1990 to 2000. [..]
In the present study, we used standard demographic survivorship metrics from the eight countries with the longest-lived populations and from the Special Administrative Region (SAR) of Hong Kong and the United States, from approximately 1990 to 2019, to address which hypothesis about human longevity is supported by these data. We then used this analysis to predict whether radical life extension is likely to occur again in this century. We used twentieth century increases in e(0) as a historical frame of reference.
[..] we found that the only populations to experience the required 0.3-year annual improvement or 3.0-year decennial improvement in life expectancy that operationally defines radical life extension were South Korea and Hong Kong. In Hong Kong, this was largely due to economic prosperity and tobacco control but, even then, only from 1990 to 2000. In every population, including Hong Kong, the most recent decade of change in life expectancy is slower than it was in the last decade of the twentieth century. In every population but Hong Kong and South Korea, the annual rise in e(0) has decelerated to below 0.2 years annually. [..]
In these populations, we found that the average probability of current birth cohorts surviving to age 100 is 5.1% for females and 1.8% for males. The highest population-specific probability of surviving to 100 occurred in Hong Kong where 12.8% of females and 4.4% of males are expected to reach age 100 in their lifetime based on life tables from 2019. Across these eight countries with the longest-lived populations and in Hong Kong and the United States, we found no population that comes close to 50% survival to age 100. [..]
If e(0) were to hypothetically reach 110 years, death rates at all ages from all causes of death combined—up to age 150 years (for example, decades beyond the observed survival distribution for humans)—would need to be 88% lower than the observed death rate at age 109 in Japan in 2019. This level of mortality would require the complete cure or elimination of most major causes of death that exist today. [..]
If death rates were zero from birth through age 50, the composite highest life expectancy at birth would be 89.7 for females and 84.7 for males. That is, reducing death rates to zero for the first 50 years of life adds 1.0 years to the composite most favorable life expectancy of females and 1.5 years to the composite most favorable life expectancy of males. [..]
First, there can be no dispute that life expectancy improvements have decelerated since 1990. Our analysis clearly demonstrates that this finding runs counter to predictions that it was going to accelerate. Where uncertainty remains is how much more survival time can be manufactured with the disease model that now prevails (shown here to have a declining influence on life expectancy) and the far greater uncertainty associated with future improvements in survival that may result from the deployment of gerotherapeutics or other advances in medicine that cannot be conceived of today. Because radical lifespan extension brought forth by yet-to-be-developed medical advances cannot be empirically evaluated over short timeframes, a limitation here (and within the field of aging in general) is that it is difficult to justify any numerical estimate of their future influence on life expectancy.
Although limits to human life expectancy were discussed previously, it is important to note that these limits do leave room for such advances in medicine (treating disease or targeting the underlying causes of aging and improved behavioral risk factors) that could further improve mortality at older ages (that is, these limits are not brick walls for longevity). Importantly, these limits should not be interpreted from an evolutionary perspective to mean that there is no longevity value in achieving grandparenthood, that the post-reproductive period should necessarily be short or that the occurrence of chronic conditions of aging are driven by a force of selection to just beyond the upper edge of the reproductive window, in accordance with the antagonistic pleiotropy, mutation accumulation and disposable soma hypotheses.
A naturally occurring life expectancy of a human population in the absence of any form of medical intervention throughout the course of life is unknown, but it would be expected to be far below the life expectancies observed in high-income nations today. As such, recent increases in e(0) are likely to be a result of the addition of what has been referred to as manufactured time—survival time brought forth by medical and public health interventions.
The notion of a limit to life expectancy present today represents something akin to a glass mortality floor or a second soft limit to longevity that has become increasingly less sensitive to modifications through the treatment of diseases but that should be amenable to modification through changes in the rate of biological aging. The evidence presented here indicates that humans are approaching a second soft limit—using the very criteria set forth by those who have argued for the last three decades that either there is no limit to human longevity or, if there is one, it was not then in sight.
[..] Results presented here indicate that there is no evidence to support the suggestion that most newborns today will live to age 100 because this would first require accelerated reductions in death rates at older ages (the exact opposite of the deceleration that has occurred in the last three decades). Furthermore, even if the 30.2% improvements in mortality in the 65-and-older population observed to have occurred in high-income nations from 1990 to 2019 occurred again, only a small fractional increase in survival to age 100 would ensue. Changes in existing institutions that rely on lifespan estimation, such as retirement planning and life insurance pricing constructed with a 100-year lifespan assumption as its foundation, are likely to be overestimating survival by a wide margin for most people.
It would be optimistic if 15% of females and 5% of males in any human birth cohort could live to age 100 in most countries in this century (even if any of the recently estimated composite best practice death rates are achieved under optimal conditions)—a limit that could theoretically be breached but only if gerotherapeutics are developed that slow biological aging. Even then, survival to age 100 for most people is not a certainty.
[..] the efforts of the National Institute on Aging Interventions Testing Program (ITP) demonstrated that potential therapies have limited efficacy in safely extending mouse lifespan. Of 50 compounds so far tested, only 12 have increased lifespan (in either sex), none by more than 15%.”
Full article, SJ Olshansky, BJ Willcox, L Demetrius and H Beltran-Sanchez. Nature Aging, 2024.10.7