When Frederick Crosby turned 100 in Thornlie, Australia, he was clear what it had got him to that age: ‘A bit of luck. There are so many things that can go wrong and they didn’t go wrong,’ he told his local newspaper.

On the other side of the world, Canadian Emily Sharpe turned 100 a couple of weeks later and expressed a similar sentiment when asked for the secret of her long life. ‘Damn luck’ she said. ‘I smoked from the time I was 14 until I was 84. That’s not fair! Some other poor bloke smoked just a a few years and he can’t breathe.’

And in Denver, Paul Marcus agrees. ‘You got to be god damned lucky for 100 years.’

So, is luck really the key to reaching 100?

Plausibility rating: 8 out of 10. Well, it’s certainly one of the keys, though it’s not quite so simple as being ‘born lucky’.

First, we need to extend the concept of ‘luck’ to include ‘chance’. There are bonfires worth of literature about the differences between these two concepts but this paper suggests that, broadly, being ‘lucky’ or ‘unlucky’ is about whether or not we benefit from the circumstances – the chance events – that come our way randomly. A lucky person seems to be affected by ‘positive’ chance events more often; an unlucky one by ‘negative’ chance events.

And our centenarians certainly do seem to have benefited from chance events, in at least three areas: their genetic inheritance; the environment in which the grew up and their exposure to – or avoidance of – some of the random events that come our way.

Genetics. Paul Marcus wouldn’t take much persuading on this one – in fact his first answer on longevity is ‘You gotta have good genes’. We’ll cover genetics in more detail in a future post but it’s fairly clear that some people are born with genes that make them more likely to live longer. One of the more interesting aspects of this is raised, albeit unwittingly, by Emily when she says that she smoked most of her life and yet has reached 100. Though smokers tend not to make it to 100 (again, a subject for a future post), some do. The world’s oldest recorded person, Frenchwoman Jeanne Calment, was a lifelong smoker until her death in 1997 at 122. It seems likely that Emily and Jeanne share a particular set of genes, which researchers suggest, allow some people to smoke but avoid the consequences to their health. This group has the same levels of inflammation, blood pressure and immune system functioning as non-smokers but it doesn’t affect them in the same way. Chance indeed.

Environment. Genetic inheritance is only the first of life’s lotteries. Where you are born and the environment you grow up in are also critical to living to 100. The so-call  ‘Preston Curve‘ demonstrates that if you are born in a relatively prosperous Western country you have a far greater chance of reaching your 100th birthday than if you are born in a poor one. A decent health service, good levels of public hygiene, adequate nutrition and housing: all of these are tip the scales significantly in your favour.

Exposure to random events. We die not just from illness and disease but from what happens around us. Every year in the UK, 18,000 people die from accidents and other external causes. Most of these are in traffic accidents and falls, but some unlucky people are poisoned, electrocuted and, of course, murdered. A few even meet their end from hornets, lightning and rat bites.  There were, of course, a number of major external events that helped shape the fortunes of the generation that is currently reaching 100: they lived (and died) through two major world war, many of them fighting in at least one of them. Both these wars had a major effect on life expectancy. In the US, for example, male life expectancy dropped in 1917 to a startling 37 from a pre-war peak of 52. In the second world war, male life expectancy in the UK fell sharply in 1940 and 1941 and in 1943 in the US (not fully recovering until 1949).

So chance, luck has clearly been a factor for our centenarians. They didn’t die of a range of diseases and they weren’t stung to death by hornets or killed in the second world war.

Yet, as the psychologist Richard Wiseman observes, people are not simply passive; they respond to  the events and circumstances they face. Being ‘lucky’ in his view is not just about what comes for way but how you make it work to your advantage (or at least mitigate its consequences).

Take the impact of the Vietnam War on the lives of young male Americans.  Surely there is no clearer example of the importance of luck on longevity than the 1969 Vietnam Selective Service Lottery, which selected the people to be drafted to fight in Vietnam? In that lottery, the 366 birth days in a year were drawn out at random, with the first dates drawn the ones who would be drafted. (You can find out what would have happened to you here – my birthday, 15th May, came out number 130 so it was more likely than not that I would have been called up).

However, while this makes it look as though being sent to Vietnam was pure chance, in practice it was not. This article explores the various strategies you could employ to avoid being drafted into the US infantry, from where most of the casualties came. You could, for example, volunteer for the airforce or navy (whose casualty rate was very low) rather than wait and run the risk of being drafted. Or you could do a deal and volunteer for a range of hard-to-recruit positions that ran no risk of combat.  And if you’d shaped your life by getting a college degree, you could almost always use this to find a safe administrative role, well away from the combat zone. As a result, of the 8.7m Americans who served in the Military, only a third went to Vietnam and, of these, only 12 percent were in combat and less than two percent were killed. So the lottery didn’t have to determine your fate.

And there is one final way in which chance is becoming less important in reaching 100. In 1932, the chances of living to 100 in the UK was around 1 in 20 for women and one in 20 for men. To get there you had to have an awful lot of things going for you. But, with advances in medicine and public health, today’s children have  a 1 in 3 chance of reaching 100.

So, in that sense, today’s children are luckier than their grandparents.