How long can people live? This is not just a foundational question in science. The answer has important public policy implications and is of interest to us all. Recent scientific evidence has revealed the answer, so whatβs next in humanityβs never-ending battle against disease and the persistent ravages of aging?
Larger increases in lifespan not likely if aging itself remains the same
In our first effort to answer this longevity question more than three decades ago, my colleagues and I estimated how much death rates would need to decline to live decades longer than we do now. The findings were unexpected. Our analysis revealed that a life expectancy of 100, for example, appeared implausible because it would require reductions in death rates greater than those achieved by curing diseases of aging.
To illustrate why this seemed improbable, we calculated the effect on life expectancy if cancer, cardiovascular diseases, and diabetes were cured individually, or collectively all at the same time. Surprising to many, curing cancer increases life expectancy by only about three years; curing heart disease only adds about 4.5 years to life expectancy; and curing all fatal diseases together produces a life expectancy at birth of about 90 years.
This naturally raised the question: if curing everything does not render us immortal or something close to it, whatβs holding us back?
The answer eventually hit us like a lightning bolt. There is an immutable force at work in humans and other species that becomes activated and visible only when enough people survive long enough to experience it. It is the aging of our bodies β the natural degradation of parts of the body that wear out over time and with use, that was barely visible throughout history because, so few people lived that long.
This phenomenon not only prevents large increases in life expectancy from occurring in the future as long as aging remains unchanged, it also meant that the rise in life expectancy must slow down in long-lived populations except under extenuating circumstances that have never occurred before. It is the biological aging of our bodies that explains why accelerating gains in life expectancy, and immortality, arenβt in the cards.
As long as aging remains unchanged, large increases in life expectancy, like those experienced in the 20th century, are unattainable.
In other words, a slowdown in the rate of improvement in life expectancy is not a sign of a failing health care system or a byproduct of harmful risk factors (like smoking or obesity) or some new toxins in our food and air. Instead, it is a signal that humanityβs battle for a long life had largely been accomplished. We estimated back in 1990 that once 95% of a birth cohort survives beyond age 65, and 80% of deaths occur between 65 and 95, life expectancy would plateau at around 85 years (88 for women and 82 for men).
A decade later, in an article in Science, we provided a 10-year check on this hypothesis using life expectancy data from Japan, France, and the U.S., and came to the same conclusions: this phenomenon of slowing increases in life expectancy had already begun.
Weβve now waited a full 34 years to look back on what actually happened following our 1990 prediction and 2001 confirmation. The results appear in a paper recently published in Nature Aging. Using data from ten long-lived populations that were first in line to benefit from accelerating advances in life-extending technologies, weβve now demonstrated definitively that the period of rapid increases in life expectancy is over.
The rise in life expectancy slowed precipitously in the very countries where it should have accelerated higher. Accompanying evidence also demonstrated that mortality is compressing into the time window between ages 65 and 95, and that it is far more difficult to raise life expectancy today than it was just three decades ago.
So, what do these observations mean exactly? Whatβs next?
First, declare victory in the pursuit of life extension
The miracle of extended life has been given to us by public health, modern medicine, and improved behavioral risk factors. If all medical interventions of every kind were removed from a population, even if everyone lived a healthy lifestyle, life expectancy would be somewhere in the 30-60-year range β which is consistent with the historical record. This means that most people now alive past age 60 are living on βmanufactured timeβ β survival time humanity has created for itself.
In practical terms, this means that the natural limit to life expectancy for long-lived human populations is well behind us β not in front of us as longevity protagonists suggest. Like stretching a rubber band, the further life expectancy extends beyond its natural limits, the more difficult it becomes to live longer.
This means the battle to achieve longer lives has been won. The time has arrived to declare victory in the pursuit of life extension. Itβs now time to extend the period of healthy life.
The failures of success
The rising prevalence of heart disease, cancer, stroke, dementia, sensory impairments, etc., is a product of success β not failure. In the early 1990s, we described this as the βexpansion of morbidity hypothesisβ, which is a cautionary note indicating we should be aware of the diseases and disorders weβre trading for in exchange for our longer lives. We werenβt the first to make this argument β the βFailures of Successβ arguments from Ernest Gruenberg, Jim Fries, and Ken Manton, led to related conclusions.
Treating one disease at a time without modulating the rate at which we age, which is a whack-a-mole approach to disease management now in place, will ultimately lead to rising levels of frailty and disability among the survivors. This is not a suggestion that humanity stop battling diseases or improving behavioral risk factors that can accelerate both disease and aging β it is a realization of the population-level health consequences of successful life extension in the absence of modifications to aging itself.
Would healthier lifestyles lead to radical life extension?
The short answer is no, but healthier lifestyles as primary prevention should always be a top priority in public health. Keep in mind that certainly in the United States, but elsewhere, harmful behavioral risk factors, such as obesity and sedentary lifestyles, have been working against the observed gains in life expectancy shown to be slowing down.
However, modern medicine moved swiftly to accommodate these health challenges through medical procedures and pharmaceuticals that have proven successful in restoring length of life close to average. Stents, statins, and blood pressure medications, among many others, are effective in saving and extending lives.
But would we be better off modifying risk factors, so these drugs arenβt needed to begin with? Of course, and thatβs the preferred path to a healthier life, but the life-extending benefits of healthier lifestyles at the population level cannot exert that strong of an influence on life expectancy for national populations that is much greater than the medical and pharmaceutical interventions already in place. However, at the individual level, their influence on health and length of life can be profound.
Does the presence of βvanguard groupsβ of longer-lived people, such as those described as living in Blue Zones, provide optimism for the future of life expectancy for national populations?
At one level, yes, because these population subgroups provide us with clues on what is theoretically possible in human bodies. Furthermore, studying vanguard groups of longer-lived people allows scientists to discover some of the genetic and behavioral risk factors that favor exceptional longevity. However, heterogeneity in survival prospects across genetically diverse populations is a natural part of human biology, so just because some people can live exceptionally long lives, does not mean everyone in a population has the opportunity to do so.
By way of illustration, some people are capable of running a mile in under four minutes, but this does not mean the rest of us can. The same holds true for vanguard longevity and its link to life expectancy. Just because the world record for human longevity is a validated 122 years by the French woman Jeanne Calment, this does not mean the life expectancies of national populations are capable of rising to the maximum lifespan for the species.
The rationale for geroscience
If there is one thing aging research has proven in the last few decades, itβs that the biological process of aging is inherently modifiable. Science and medicine can shape and mold this process just as we have done for major fatal diseases, so one obvious path forward is to change the rules of the whack-a-mole game by bringing in a new hammer with multiple heads that hit all the moles at once.
There is no shortage of pathways to a successful gerotherapeutic because the door is wide open β natural selection could not have given rise to brick walls for longevity or aging time bombs that are set off beyond a certain age. Combine this with empirical evidence suggesting that the economic value of extending healthspan is, at a minimum, $38 trillion for just one year of healthy life, and the conditions are ripe for investments in aging interventions and the healthspan they will manufacture. Geroscience has the potential to redefine what it means to grow old.
