‘The trouble with the world is not that people know too little; it’s that they know so many things that just aren’t so.’
There is no famous quote better than the Mark Twain one above that exemplifies the level of misinformation and half-truths that permeate the common understanding of human ageing and longevity.
My own father held the beliefs that ageing is caused by gravity — mother nature’s way of returning us to the ground from which we came — that colds are caused by walking outdoors with bare feet; that we shouldn’t exercise so as not to use up our limited allotment of heartbeats; and that applying a rag soaked in WD40 to one’s knees alleviates the pain caused by arthritis. He lived proudly and happily to the ripe old age of 96, so I never had the heart to do much more than smirk and nod.
The media is constantly seeking out the sage advice of living centenarians by asking them what the secret is to their exceptional longevity. The irony in this question is the fact that many exceptionally long-lived people have atrocious lifestyles.
By far my favourite quote about ageing and longevity comes from Warren Buffett, the CEO of Berkshire Hathaway. In an interview with Fortune magazine he made the following statement:
‘I checked the actuarial tables, and the lowest death rate is among six-year-olds. So I decided to eat like a six-year-old. The octogenarian adds, ‘It’s the safest course I can take.’
Buffett’s daily routine is to drink five cans of whole sugar Coca-Cola along with eating ice cream and potato sticks (perhaps it’s no coincidence that he owns large blocks of stock in the companies that produce these foods). This profound perversion of life table statistics confounded by personal financial interest demonstrates just how misinformed the public is about the phenomenon of biological ageing and risk factors for diseases that all of us experience.
So what, then, is the real secret to longevity? The glib answer often given by gerontologists is to choose long-lived parents, which is equivalent to saying that inherited genes drive the process, and that if your blood relatives lived a long life, chances are you will as well.
But this is not a satisfying or even accurate answer for a variety of reasons, the most important of which is that it ignores the critical importance of lifestyle. If there is one thing that epidemiology and public health have taught us, it’s that how we choose to live our lives and the environment into which we are born can profoundly influence our health and longevity — but it’s not quite that simple either. So, here’s the answer in a nutshell.
How long most sexually reproducing species live, including humans, is calibrated to something that has absolutely nothing at all to do with how we live our lives. Here’s the chain of reasoning. The level of hostility in the environment that existed when each species arose had a direct and profound influence on when reproduction begins. A hostile environment where predation is common leads to early reproduction and the accompanying biology and physiology that supports rapid physical development. An example would be a mouse — a meal for many other living things. As a result mice develop and reproduce quickly: they go through puberty at 30 days and live for about three years in protected environments.
A relaxed environment with few predators allows other species to develop and reproduce later, with an accompanying life history strategy, biology, and physiology that support later development. An example would be a Greenland shark — an animal that has few predators. Thus it does not go through puberty until 176 years of age and can live for 400 years.
Human reproduction and longevity are somewhere between a mouse and a Greenland shark. The point here is that duration of life is calibrated to reproduction; reproduction is calibrated to the level of hostility in the environment; human physiology and body design evolved to accommodate these unique life history traits; and therefore the secret to species-specific longevity rests within a set of fixed genetic programmes for early life developmental events over which we have no control. Thus, while natural selection could not have given rise to ageing or death programmes, ageing happens anyway as an indirect byproduct of biological clocks that regulate developmental events early in life.
So, where does lifestyle come into play? I’ve been making the case for decades now that the only control humanity has over our personal duration of life is to shorten it, which is to say that the adoption of unhealthy lifestyles can hasten the process of ageing. It’s easy to die early. Just pick up any one of a dozen harmful behavioural risk factors that your mother told you to avoid (smoking, drugs, eating too much food or doing just about anything in excess).
What’s difficult is figuring out how to leverage your genetic heritage to maximise the genetic potential for longevity you were born with. The good news here, of course, is that because there is no genetic programme for ageing, behavioural interventions can help us live longer and healthier lives.
Keep in mind that the presence of genetic diversity means that some people can smoke and live long (the longest-lived person in the world, Jeanne Calment, lived for 122 years and smoked for 100 of them); while others can live a healthy lifestyle and die early (Jim Fixx). The fact is, no one has a chance to live an exceptionally long life unless they won the genetic lottery at birth, which is to say that one begins by choosing long-lived parents, and then listens to their advice by avoiding the harmful behavioural risk factors that shorten life.
The longer we live, the more important genetics becomes in determining duration of life. Once you’ve made it to about age 80, time has already informed you that you’re part of the longer-lived subgroup of the human family.
The take-home message on the secret to longevity is therefore surprisingly simple. Adopt a healthy lifestyle early to maximise your longevity potential; time will reveal to you whether you belong to a long-lived subgroup of the population; and, by the time you reach the age when you know the answer to this question, you’ll already be old enough to know that most of what you thought you knew about human ageing is probably wrong.
S Jay Olshansky is a professor in the School of Public Health at the University of Illinois at Chicago