What if ageing wasn't a natural part of life but disease that could be treated?

David Sinclair, a leading scientist in the field of ageing, believes just that and his life's work is dedicated to reversing the clock.

He argues that we can double our life expectancy and live healthy, active lives until we die.

The Australian runs labs at Harvard Medical School and at the University of New South Wales. He made Time magazine's list of the 100 most influential people in the world in 2014.

In an extract from his new book, Lifespan: Why We Age - and Why We Don't Have To, Sinclair details how we may live to 150.

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Let's do a little maths.

And let's make it conservative maths. Let's assume that each of these vastly different technologies emerging over the next 50 years independently contributes to a longer, healthier lifespan.

David Sinclair with his wife Sandra Luikenhuis. Photo / Getty
David Sinclair with his wife Sandra Luikenhuis. Photo / Getty

DNA monitoring will soon be alerting doctors to diseases long before they become acute. We will identify and begin to fight cancer years earlier. If you have an infection, it will be diagnosed within minutes.

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If your heartbeat is irregular, your car seat will let you know. A breath analyser will detect an immune disease beginning to develop. Keystrokes on the keyboard will signal early Parkinson's disease or multiple sclerosis.

Doctors will have far more information about their patients — and they will have access to it long before patients arrive at a clinic or hospital.

Medical errors and misdiagnoses will be slashed. The result of any one of these innovations could be decades of prolonged healthy life.

Let's say, though, that all of these developments together will give us a decade.

Once people begin to accept that ageing is not an inevitable part of life, will they take better care of themselves? I certainly have. So, too, it seems, have most of my friends and family members. Even as we have all stepped forward to be early adopters of biomedical and technological interventions that reduce the noise in our epigenomes and keep watch over the biochemical systems that keep us alive and healthy, I've noticed a definite tendency to eat fewer calories, reduce animal-based aminos, engage in more exercise, and stoke the development of brown fat by embracing a life outside the thermoneutral zone.

These are remedies available to most people regardless of socioeconomic status, and the impact on vitality has been exceptionally well studied. Ten additional healthy years is not an unreasonable expectation for people who eat well and stay active. But let's cut that by half. Let's call it five.

That's 15 years.

Molecules that bolster our survival circuit, putting our longevity genes to work, have offered between 10 and 40 per cent more healthy years in animal studies. But let's go with 10 per cent, which gives us another eight years.

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That's 23 years total.

How long will it be before we are able to reset our epigenome, either with molecules we ingest or by genetically modifying our bodies, as my student now does in mice? How long until we can destroy senescent cells, either by drugs or outright vaccination? How long until we can replace parts of organs, grow entire ones in genetically altered farm animals, or create them in a 3D printer? A couple of decades, perhaps. Maybe three.

One or all of those innovations is coming well within the ever-increasing lifespans of most of us, though. And when that happens, how many more years will we get? The maximum potential could be centuries, but let's say it's only 10 years.

That's 33 years.

At the moment, life expectancy in the developed world is a tad over 80 years. Add 33 to that.

That's 113 years, a conservative estimate of life expectancy in the future, as long as most people come along for the ride. And recall that this number means that over half the population will exceed that number. It's true that not all of these advances will be additive, and not everyone will eat well and exercise. But also consider that the longer we live, the greater chance we have of benefiting from radical medical advances that we cannot foresee. And the advances we've already made are not going away.

That's why, as we move faster and faster toward a Star Trek world, for every month you manage to stay alive, you gain another week of life.

Forty years from now, it could be another two weeks. Eighty years from now, another three. Things could get really interesting around the end of the century if, for every month you are alive, you live another four weeks.

Jeanne Calment, who was the world's oldest person. Photo / Getty Images
Jeanne Calment, who was the world's oldest person. Photo / Getty Images

This is why I say that Jeanne Calment, who may have had the longest lifespan of any person on our planet - she died in 1997 aged 122 and 164 days - will eventually fall off the list of the top 10 oldest humans in history. And it won't be more than a few decades after that she will leave the top 100. After that, she will leave the top million.

Imagine if people who have lived beyond 110 had had access to all these technologies. Could they have made it to 120 or 130?

Perhaps.

Fellow scientists often warn me not to be so publicly optimistic. "It's not a good look," one well-meaning colleague recently told me.

"Why?" I asked.

"Because the public isn't ready for these numbers."

I disagree.

Ten years ago, I was a pariah to many of my colleagues for even talking about making medicines to help patients. One scientist told me that our job as researchers is to "just show a molecule extends lifespan in mice, and the public will take it from there." Sadly, I wish that were true.

Today, many of my colleagues are just as optimistic as I am, even if they don't admit it publicly. I'd wager that about a third of them take metformin or an NAD booster. A few of them even take low doses of rapamycin intermittently. International conferences specifically about longevity interventions are now held every few weeks, the participants not charlatans but renowned scientists from the world's most prestigious universities and research centres. In these gatherings, it is no longer unusual to hear chatter about how raising the average human lifespan by a decade, if not more, will change our world. Mind you, the debate is not about whether this will happen; it is about what we should do when it happens.

The same is increasingly true among the political, business, and religious leaders with whom I spend more and more of my time these days, talking not just about new technologies but about their implications.

Slowly but surely, these individuals — legislators, heads of state, CEOs, and thought leaders — are coming to recognise the world-changing potential of the work being done in the field of ageing, and they want to be ready.

All these people might be wrong. I might be wrong. But I expect to be around long enough to know one way or the other.

American physicist Albert Michelson won a Nobel Prize for measuring the speed of light. Photo / Wikipedia
American physicist Albert Michelson won a Nobel Prize for measuring the speed of light. Photo / Wikipedia

If I am wrong, it might be that I was too conservative in my predictions. Though there are many examples of false predictions — who can forget nuclear-powered vacuum cleaners and flying cars? — it is far more common for people not to see something coming. All of us are guilty of it. We extrapolate linearly. More people, more horses, more horse manure. More cars, more air pollution, always more climate change. But that's not how it works.

When technologies go exponential, even experts can be blindsided.

The American physicist Albert Michelson, who won a Nobel Prize for measuring the speed of light, gave a speech at the University of Chicago in 1894, declaring that there was probably little else to discover in physics besides additional decimal places.

He died in 1931, as quantum mechanics was in full swing. And in his 1995 book, The Road Ahead, Bill Gates made no mention of the internet, though he substantially revised it about a year later, humbly admitting that he had "vastly underestimated how important and how quickly" the internet would come to prominence.

Kevin Kelly, the founding editor of Wired magazine, who has a better track record than most at predicting the future, has a golden rule: "Embrace things rather than try and fight them. Work with things rather than try and run from them or prohibit them."

We often fail to acknowledge that knowledge is multiplicative and technologies are synergistic. Humankind is far more innovative than we give it credit for. Over the past two centuries, generation after generation has witnessed the sudden appearance of new and strange technologies: steam engines, metal ships, horseless carriages, skyscrapers, planes, personal computers, the internet, flat-screen TVs, mobile devices, and gene-edited babies. At first, we are shocked; then we barely notice.

Microsoft founder Bill Gates. Photo / Getty Images
Microsoft founder Bill Gates. Photo / Getty Images

When the human brain was evolving, the only things to change in a lifetime were
the seasons. It should come as no surprise that we find it hard to predict what will happen when millions of people work on complex technologies that suddenly merge.

No matter if I'm right or wrong about the pace of change, barring a war or an epidemic, our lifespan will continue to rise. And the more thought leaders I speak to around the globe, the more I realise how vast the implications are. And yes, some of those people have allowed me to think and plan for events well beyond the initial scope of my research.

But the people who push me to think even harder are the younger people I teach at Harvard and other universities, and the often even younger people I hear from via email and social media nearly every day. They push me to think about how my work will impact the future workforce, global health care, and the very fabric of our moral universe — and to better understand the changes that must take place if we are to meet a world of significantly prolonged human healthspans and lifespans with equity, equality, and human decency.

If the medical revolution happens and we continue on the linear path we're already on, some estimates suggest half of all children born in Japan today will live past 107.4. In the United States, the age is 104.

Many researchers believe that those estimates are overly generous, but I don't. They might be conservative. I have long said that if even a few of the therapies and treatments that are most promising come to fruition, it is not an unreasonable expectation for anyone who is alive and healthy today to reach 100 in good health — active and engaged at levels we'd expect of healthy 50-year-olds today.

One hundred and twenty is our known potential, but there is no reason to think that it needs to be for the outliers. And I am on record as saying, in part to make a statement and in part because I have a front-row seat on what's around the corner, that we could be living with the world's first sesquicentenarian. If cellular reprogramming reaches its potential, by century's end 150 may not be out of reach.

At the moment I write this, there is no one on our planet — no one whose age can be verified, at least — who is over the age of 120. So it will be several decades, at least, before we know if I'm right about this, and it could take 150 years before someone steps over that threshold.

But as for the next century? And the next? It is not at all extravagant to expect that someday living to 150 will be standard. And if the information theory of ageing is sound, there may be no upward limit; we could potentially reset the epigenome in perpetuity.

Calment pictured as a young woman. Photo / AP
Calment pictured as a young woman. Photo / AP

This is terrifying to a lot of people — and understandably so. We're on the cusp of upending nearly every idea we've ever had about what it means to be human. And that has a lot of people saying not just that it can't be done but that it shouldn't be done — for it will surely lead to our doom.

The critics of my life's work aren't nameless, faceless social media trolls. Sometimes they are my colleagues. Sometimes they are close personal friends.

And sometimes they are my own flesh and blood.

Our oldest child, Alex, who at 16 hopes for a career in politics and social justice, has often struggled to see the future with the same optimism I do. Especially when you're young, it is hard to see much of an arc to the moral universe, let alone one that bends toward justice.

Alex grew up, after all, in a world that is quickly and disastrously warming; in a nation that has been at war for the better part of two decades; and in a city that suffered a terrorist attack on the people participating in one of its most cherished traditions, the Boston Marathon. And like so many other young people, Alex lives in a hyperconnected universe where news of one humanitarian crisis after the next, from Syria to South Sudan, is never far from the screen of a smartphone.

So I understand. Or I try to, at least. But it was disappointing to learn, one recent night, that Alex didn't share the optimism I've always had about the future. Of course, I'm proud that our kid has such a strong moral compass, but it was saddening to realise this more pessimistic view of the world casts a significant shadow over the way Alex sees my life's
work.

"Your generation, just like all the ones that came before, didn't do anything about the destruction that is being done to this planet," Alex told me that evening. "And now you want to help people live longer? So they can do even more damage to the world?"

I went to bed that night troubled. Not by our firstborn's denouncement of me; of that, I admit, I was a little proud. We'll never destroy the global patriarchy if our children don't first practice on their fathers. No, what I was troubled by—what kept me up that night and has done so many since — were the questions that I simply could not answer.

Most people, upon coming to the realisation that longer human lives are imminent, also quickly recognise that such a transition cannot possibly occur without significant social, political, and economic change. And they are right; there can be no evolution without disruption. So what if the way I see the future isn't at all what we're headed toward? What if giving billions of people longer and healthier lives enables our species to do greater harm to this planet and to one another? Greater longevity is inevitable; I'm sure of it. What if it inevitably leads to our self-destruction?

What if what I do makes the world worse?

There are plenty of people out there — some of them very smart and very informed — who think that's the case. But I'm still optimistic about our shared future. I don't agree with the naysayers. But that doesn't mean I do not listen to them. I do. And we all should.

Lifespan by David Sinclair
Lifespan by David Sinclair

Lifespan: Why We Age and Why We Don't Have To
By David Sinclair
RRP: $32.99
HarperCollins Publishers