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Healthy Aging & Lifestyle

How Long Can We Live?

By Jim Mellon, Al Chalabi
As lifespans continue to lengthen, might it become common to live to 100, or even older? Other species live hundreds of years, so why can’t humans? Anything is possible. What was once viewed as science fiction might turn out to be fact.

The fact that we age remains unavoidable. The question is how long can we live? Centenarians exist, although they are far from the norm. But as lifespans continue to creep upward across the globe, is it possible that it might become par for the course to live to be 100? Are predictions that we might reach 110 or 135 years of age — or older — within the realm of possibility? And if so, how is this possible?

Science suggests that there will soon exist the technology to advance human lifespan to beyond the longest ever recorded age. In fact, we have the makings of that technology now. Future therapeutics or interventions could take us even farther past these historical hard limits, although, admittedly, trying to predict how soon that might occur leaps into the realms of pure conjecture. But however the future plays out, thanks to a steady stream of recent scientific discoveries, achieving an average human lifespan of around 110 years is a realistic prospect.

LONGEVITY ON THE PLANET

It is commonly believed that the longest-lived person with a validated birth and death was a super-centenarian from France, Jeanne Calment, who is thought to have lived to be 122.1 Those claims that Calment lived to be that old have recently been disputed in an analysis in the journal Rejuvenation Research (although that counterclaim was then refuted). No matter what the exact age of the oldest recorded person might be, there is no doubt that the number of centenarians is on the rise. And the number of super-centenarians (those over 110 years of age) is bumping up, too.2,3,4,5

We live long lives compared to most species on the planet, but humans are by no means the longest-lived. Although almost all organisms appear to die at some point, some have exceptionally long lives. And some are capable of dramatic regeneration, even after suffering major injury or trauma.

Some trees can live exceptionally long. For example, the ginkgo biloba can live for over 1,000 years, and the deep sea sponge, considered to be an animal, is estimated to live for more than 10,000 years. Living creatures can have super-extended lifespans, too. Hydra (a relative of the jellyfish) is one such example, living to around 1,400 years, as are tortoises, turtles and some whales, who can reach 150 to over 200 years old. The Greenland shark can live to be an estimated around 400 years old. Sturgeon fish can live to be 125. Jellyfish are sometimes considered to be immortal because in times of stress they can preserve their lives by reverting back to a more immature polyp stage.6,7,8,9,10,11,12,13 The bad news is that there can be no true immortality for humans in our current form. Immortality would require us to change all of our cells, all of our organs and, most improbably, our brains, which represent our “self.”

But longevity doesn’t have to mean forever; it means living longer than we currently do. Those centuries-long lives suggest that some creatures have overcome some obstacle to longevity that humans have not. So, if other species can live ultra-long lives, why can’t we? Research indicates that lifespan (and, more importantly, healthy lifespan, or “healthspan”) is on the verge of a significant shift upwards, possibly by more than 30%.14

LIMITS TO LONGEVITY?

There are plenty who doubt that humans are on the verge of an extended-lifespan revolution, including some genuine luminaries of the scientific world. A dwindling band of scientists believe that the Second Law of Thermodynamics, combined with the fact that our technological toolkit is still relatively primitive, will make life extension beyond 120 impossible for many years to come, except for some very rare outliers.

According to the Second Law of Thermodynamics, everything eventually crumbles — tables, chairs, roads, ships, cars — and us. The theory states that the total entropy (disorder, or randomness) of an enclosed system (for instance, the universe) always increases with time, or, in ideal conditions if a steady state can be maintained, stays constant. We here on Earth live in a physical system that is not enclosed because it is constantly receiving energy from the sun and in turn giving some of that energy up to space. This means more chaos — and bodies that age, rather than remain in some orderly system of health.

This theory makes the point, inaccurately but succinctly, that with age and prolonged exposure to the Second Law’s effects, homeostasis, or the condition of a steady state, gradually collapses. So, age and death are inevitable.

There are some indicators that we do follow this path. Normally, our steady state in adulthood is perturbed when we start to rapidly decline after age 60 — in a highly visible and precipitous way as the body weakens and diseases manifest. It is at this point of more rapid atrophy that we tend to lose metabolic functioning, weakening the systems which allow us to perform normal and efficient cellular repairs. We then become the victims of what has been described by Dr. David Sinclair, PhD, a professor of genetics and the co-director of the Paul F. Glenn Center for the Biology of Aging at Harvard Medical School, as “epigenetic noise.” This is the cumulative randomization of genomic behavior that results from being alive for six decades or more. Although in the developed world we generally live for another 23 years after hitting 60, for the last two decades of our lives most of us are likely to suffer the increasing burden of the diseases of aging.

One longevity doubter, Dr. Jan Vijg, PhD, of the Albert Einstein College of Medicine in New York, is convinced that the human body has innate limits. Not only is there a noticeable decline for most in their 60s through their 90s, people who make it to beyond 115 are rare, and life expectancy even for them is highly limited thereafter. It appears that the longest-living person that has been officially verified lived to be 116 years, although some claims have been made of two individuals living to be 118.15

Dr. Vijg believes that average life expectancy, and indeed average healthspans, can and will increase but that the upper limit is about 115, after which our bodies will simply collapse and die. According to Vijg and his fellow Einstein researchers, this upward arc for maximal lifespan has a hard ceiling, and some people, though not most, have already touched it. Dr. Vijg concluded this using data from the Human Mortality Database, which compiles mortality and population data from more than 40 countries. This data suggests that, since 1900, survival improvements for people 100 or over have been more or less maximized, and that the chance of anyone in the foreseeable future living over 125 anywhere in the world is only one in 10,000.16

Most scientists share the contention that we are selected for reproduction, and that when we have reproduced we have no further utility so we age and die. Of course, the fact that we can live much longer after reproduction seems to suggest otherwise. But those in this camp believe that aging has no useful evolutionary function, although some conclude that aging could be and should be considered a treatable syndrome.17

The Second Law would seem to suggest that to reverse the molecular degradation that accompanies aging, we would have to find a way to keep cells healthy for longer, or forever, or to replace all of the cells, organs and tissues that make us who we are, and do so on a regular basis. That would include the cells that typically don’t often divide, or don’t divide at all, such as heart cells and neurons/brain cells.

LONGER LIFESPANS ARE POSSIBLE

Dr. Judith Campisi, PhD, is a respected scientist from the Buck Institute for Research on Aging near San Francisco, one of the most important centers for aging research.* Professor Campisi believes that the aging process is becoming postponed and will be postponed even further in coming decades. But she cautions that further gains in maximal lifespan will have to come through the modification of genomes. She is pessimistic on the timing of this as she rightly points out that there are multiple genes implicated in aging. So, it will be hard to modify most — or all of them, even within the space of two generations.

Does the ability of humans to live longer lie in our genetics? If so, perhaps we can live longer with only a few genetic tweaks. Or perhaps other factors affect whether we can — and how far we can — push back the clock.

The optimistic camp is gaining traction. Dr. Tom Kirkwood, PhD of Newcastle University in the UK, an important opinion leader in the longevity field, disputes the notion that there is a limit to human lifespan: “The idea that life is limited does not really fit with what we already know about the biology of the aging process. There is no set program for aging — the process is driven by the build-up of faults and damage in the cells and organs of the body, which is malleable.”

This malleability of our bodies provides the main grounds for optimism. If science can change our fundamental path, it changes the world.”

Aging appears to be a function of evolutionary neglect, (i.e., evolution has no reason to prevent it).18 So, it’s entirely possible that, at some point in the future, the basic mechanisms of getting older will be understood, slowed and halted — or even reversed. That point of reversal is some way away, and may never be achieved. But it cannot be ruled out.

Though estimates of timeframes are immensely speculative, here is what’s possible: the coming improvement in lifespans and healthspans is about 20 years away and will mean that average life expectancy (the typical person’s age at death, regardless of health) around the world will rise. In the United States, life expectancy at birth is about 78.7 years and is expected to rise to close to 100 around the world, and in developed countries, it will rise to over 110 at around that same time. This is not some sort of outlandish fiction — it has a very good chance of happening.19

HOW WILL IT HAPPEN / HOW WILL WE LIVE LONGER?

This change in lifespan will be the result of the most important scientific developments in history. It will alter the whole trajectory of our lives, and also the ways in which our physical and societal world operates. It will be achieved partly by improving the environment (the sum of factors like lifestyle choices and exposure to pollutants that currently lead to exogenous DNA damage and disease), and also by new drugs and interventions that will manipulate the molecular pathways known to be implicated in aging.

We, as a species, are going to live longer, and it will happen in stages: first, the attainment of 100 as a regular and unsurprising event; second, far more people living to what is currently considered effective maximal lifespan, that being around 115; and third, attainment of “longevity escape velocity” (a term coined by Dr. Aubrey de Grey, PhD, a biomedical gerontologist) to take us to a currently unimaginable longevity.20 If you can survive a full 30 years, there is a chance that you might live to, say, 150. Why not? This third one remains in the realm of aspiration, but there is always the chance.

Within decades from now, a fresh understanding of the principles of cell biology will allow for the manipulation of age-specific pathways and of so-called cell senescence — which, combined, will take mankind beyond the record of 122 that Jeanne Calment is thought to have set over two decades ago.

We are already benefiting from the gradual erosion of the effects of the key diseases related to aging. Cancer, now often viewed as a broad spectrum of around 200 individual diseases, and caused by multiple different factors, will cease to be the death sentence it once was. In fact, within two decades, cancer will not be among the leading causes of death. Immunotherapies are becoming increasingly sophisticated, and early diagnosis of cancer will soon become a clinical norm.

All the chronic diseases of aging, such as cardiovascular disease and diabetes, are benefiting from medical advancements so that people are living longer with the conditions and may not die from them, although the elimination of all the key diseases of aging would not be enough to confer in itself a huge increase in average life expectancy. Even if these diseases could be completely eliminated, this would confer a maximum of about 15 years of extra life to human beings, a figure well below the 30 extra years that is genuinely possible in the relatively short term. And deaths that will always happen simply because our bodies are fragile — from murders, accidents, suicides — will be with us for all time as far as anyone can tell. That said, if you can stay alive for another 10 to 20 years, and if you aren’t yet over 75, and if you remain in reasonable health for your age, you have an excellent chance of living to over 110 years old.

TRAJECTORY OF LIFE

As things stand now, humans are born and undergo a physiological growth period. Upon adulthood, they exist in a steady state of homeostasis. That is eventually perturbed, leading to sickness, decline and, eventually, death. Continuous exposure to environmental influences, both from personal lifestyle choices and actual environmental assaults (like radiation, toxins and pollution), can cause internal DNA damage which can be resisted or repaired up to a point. But eventually homeostasis cannot persist, and so the processes of aging appear to become irreversible. Lifespan is the result of the speed at which wear and tear outrun repair. Our current limiting factor is that, for most, wear and tear take over.

Humans live their lives in three stages, in a way that parallels this physiological progression. During the growth period they experience infancy and education. As homeostasis sets in, they work, and as that steady state gets disrupted and the body breaks down, they live in retirement: leading up to eventual death.

But this sociological progression is not a biological imperative. What if the predicted wear and tear were stalled, or even eradicated? How life is structured now is merely a conformist response to the current, highly ordered view of society which dictates that lifespan is preordained, within certain parameters. But as people’s lifespans increase, societies will start to rethink the fundamental tenets of this traditional perspective that life consists of growth, homeostasis and decline.

If lifespans dramatically increase, the implications for populations everywhere across the globe are tremendous: education will be continuous throughout life, family life will likely be very different, and work will be something that goes on way beyond the retirement ages currently seen in developed economies; multiple careers are an option. The incremental addition of 30 years or so to average lifespans over the next two or three decades has the potential to change life — and society — in dramatic ways. Populations living longer will represent the single greatest opportunity in recorded history for all aspects of life. Everything may change because life as we know it will be dramatically altered. As with so much technology in recent years, the realization of this vision is now becoming a blurry possibility, and although the ways in which it will happen are unclear, and it may seem completely implausible to some, it will happen. Viva La Vida!

*Author Jim Mellon is on the board of trustees of the Buck Institute for Research on Aging.

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