A man's risk of dying was six times higher than normal in the year following the death of a spouse or partner. Photo / 123RF
Assuming there's such a thing as a battle of the sexes, then women have won it hands down by the time they get to 100.
In almost every country, most centenarians are female. On average, they outnumber men by four or five to one.
Males may be stronger. They may be taller. They may be better at hand-to-hand combat, more likely to earn better wages and are far more numerous in the boardroom. But when all is said and done, they do appear to be the weaker sex.
So why do so few of them make a century? And what have women got - beyond the obvious - that leaves the male sex trailing in their wake? There's no single answer, of course, but there are many surprising reasons why so many of the 14,570 centenarians in Britain are women.
Three decades ago, the view was that men's lifestyle was to blame. Young men took more risks on the road, did more dangerous jobs, got into more fights, and were more likely to go to war. This could lead to life-shortening trauma or death.
Also, men smoked and drank more and subsequently built up health problems that killed them in greater numbers after their mid-50s. But were these the only reasons that women began to outnumber men really significantly around retirement age?
In the Eighties, British physician and geneticist Sir Cyril Clarke suggested another theory: once men start drawing their pensions, they tend to adopt an unhealthy lifestyle.
They run to fat because they start sitting around, watching TV and eating too much. And they're not only less active physically but also mentally.
Three decades ago, the view was that men's lifestyle was to blame. Young men took more risks on the road, did more dangerous jobs, got into more fights, and were more likely to go to war. This could lead to life-shortening trauma or death.
Also, men smoked and drank more and subsequently built up health problems that killed them in greater numbers after their mid-50s. But were these the only reasons that women began to outnumber men really significantly around retirement age?
In the Eighties, British physician and geneticist Sir Cyril Clarke suggested another theory: once men start drawing their pensions, they tend to adopt an unhealthy lifestyle.
They run to fat because they start sitting around, watching TV and eating too much. And they're not only less active physically but also mentally.
They're also more prone to perinatal brain damage, cerebral palsy and congenital deformities.
In addition, girls develop faster in the womb, so a newborn girl can be the physiological equivalent of a four to six-week-old boy. Later, they walk and talk before boys.
It gets worse. Boys are about 25 per cent more likely to die in the first year of life. Even if they survive, they're three to four times more at risk than girls of finding their development hindered by hyperactivity, autism, Tourette's syndrome, stammering or being slow at picking up reading.
At least there's one area in which boys are ahead: they're much quicker to expose themselves to danger.
By the time they reach their mid-teens, a "testosterone storm" takes control, as hormone levels peak. This, says longevity researcher Tom Perls, "can induce some pretty dangerous behaviour among young men. They don't wear their seatbelts; they drink too much alcohol; they can be aggressive with weapons and so on."
But there may be another reason for this volatile behaviour. Some scientists put it down to slower development of the frontal lobes of the male brain, which deal with responsibility and evaluating risk.
Men are also three times more likely to take illegal drugs than women, according to official figures for England and Wales. Plus they're three times more likely to kill themselves; between 2001 and 2011, more than 38,600 males over the age of 15 committed suicide.
The upshot of all this is that, between the ages of 15 and 30, the death rate for males is more than twice that of females. So, by age 30, women are already starting to outnumber men.
That trend continues throughout the rest of their lives, with fewer women than men dying at almost all ages.
The workplace is more dangerous for men. From 2013-14, 20 times as many men as women were killed at work. Men also tend to get exposed more to hazardous substances that can damage their long-term health. But it's from the age of 55 or 60 that the gap starts to widen.
That's when the unhealthy lifestyle of some men starts to take its toll, particularly through heart disease and strokes.
While these killers claim men in significant numbers in their 50s and 60s, women don't usually fall victim for at least another ten years. Yet, if something's worrying her, a woman is more likely to go to a doctor than a man and get the condition treated.
Dr Marianne Legato, director of America's Foundation for Gender-specific Medicine, says: "Men often deny illness. They minimise symptoms because they don't want to go to a doctor and find out something is wrong."
Women are not only more pragmatic, but they often nurse and support each other when they're ill - looking after other women's children, laughing and crying together, and boosting each other's confidence. So they're much more social in the way they cope with stress or things going wrong in their lives.
Men, on the other hand, are more likely to have a "fight or flight" mentality - reacting to problems with aggression or withdrawal, both of which can negatively affect their health. This difference alone, say scientists, is a significant part of the reason why women generally live longer than men - and are more likely to become centenarians.
For instance, a massive study concluded in 2010 that having plenty of friends reduced our chances of dying early, while being lonely was as harmful as smoking 15 cigarettes a day, and twice as dangerous as obesity.
Having intimate friendships also helped women deal with loss. This is plainly crucial if you want to live to 100, because you're likely to outlive your spouse, siblings, friends, maybe children and even grandchildren.
Many elderly men fail to cultivate social networks. A Dunfermline study of more than 100 retired males found that 60 per cent said they missed their workmates, and three-quarters said they'd made no new friends.
Instead, they depended heavily on their spouses for emotional support. And, as one scientist remarked: "When a man loses his primary female partner, he's in trouble."
Longevity researcher Tom Perls agrees. If a man's wife survives to old age alongside him, he says, his chances of living to 100 will improve significantly.
But, he says, "the loss of a wife is usually too high a hurdle for men to clear". On the other hand, a woman who's lost her husband is 'usually able to continue the race independently'.
In fact, a man's risk of dying was six times higher than normal in the year following the death of a spouse or partner, according to investigators at London's Cass Business School.
For women, the risk of dying only doubled. So there are plenty of differences in lifestyle that may explain why so many more women make it to 100.
But is there something more - something that occurs in adulthood - which gives men a disadvantage?
Professor David Goldspink, at Liverpool John Moores University, spent two years studying 250 healthy volunteers aged 18-80.
He found the male heart declines in power by 20-25 per cent between the ages of 18 and 70, while the female heart carries on merrily.
The reason? As they age, men lose about a third of the muscle in the walls of their hearts, while women lose hardly any.
Other researchers looked again at the male sex hormone testosterone - this time in older men. And they realised that it increased levels of harmful cholesterol and raised the risk of heart disease or stroke.
By contrast, the female hormone oestrogen lowers harmful cholesterol and raises "good" cholesterol levels.
Evidence is also emerging to suggest that male immune systems are weaker. The inflammation that raises our temperature when we're unwell is the body's first line of defence against infection, because heat can often kill off the invading agent. But humans carry an enzyme that can block the inflammation process.
Experiments on mice seemed to show that the female sex hormone oestrogen prevents this enzyme from interfering with inflammation. Hence females have a more powerful inflammatory response - which means they have a stronger immune system.
And that's not all. Research in Tokyo found that "T-cells" - which protect us from infection - decline faster in men than in women. Two other types of cell in the body's defence armoury become more numerous as we get older - but the increase is bigger in women.
Japanese scientists concluded that these findings were "consistent with the fact that women live longer than men".
In the UK, researchers at Imperial College of Medicine came to a similar conclusion. Moreover, they discovered that from 1993-1998, more men than women died from influenza and pneumonia.
The bad news for men kept coming: an American study of 12,000 men and women revealed that the more muscular men were, and the more sexual partners they'd had, the weaker their immune systems tended to be.
However, women have a slower metabolism than men, and scientists became convinced that this extended their lifespan. Even women's monthly periods seemed to confer an advantage.
This is because premenopausal women have about 20 per cent less blood in their bodies than men, which lowers the amount of iron in the body - a mineral that helps to form free radicals, which can damage healthy cells.
Such findings concur with studies in Finland and the U.S. which concluded men who made frequent blood donations had greater resistance to free radicals than other males. Deep in our cells, there are also other microscopic differences between the sexes.
Men have an X and a Y chromosome, whereas women have two X chromosomes.
In recent years, interest has grown in the role of women's second X chromosome, with suggestions that its genes increasingly kick in to take over from damaged ones on the other chromosome. If this is true, it represents another considerable advantage for women.
Animal studies appear to bear this out. Nearly all female mammals have two X chromosomes - and tend to outlive males. Female macaque monkeys, for instance, live about eight years longer, while female sperm whales live an average 30 years longer than males.
Then there are telomeres, the sections of DNA that protect the ends of chromosomes from decay. Those belonging to men are shorter and degrade more quickly - which may lead to men ageing faster.
So, as female centenarians proliferate, are we destined to become an ever more female-dominated society? Not exactly - despite all the disadvantages of their sex, men are slowly gaining on women in the longevity stakes.
This is partly because the decline in heavy industries has reduced the risk to men, and partly because men are now doing more exercise.
But possibly the most important factor is that women are starting to behave more like men. And not in a good way.
Women are drinking more, smoking more, and marrying later than they used to. The number of women dying of liver cirrhosis has risen 37 per cent in ten years, while between 1970 and 2009, the rate at which they've been affected by lung cancer has increased by 72 per cent - while men's has dropped by more than half.
Then there's the issue of obesity.
Of course, both men and women suffer - but being grossly overweight seems to be more damaging for females. An obese woman is 12.7 times more likely to develop type 2 diabetes than one of normal weight. For a man, the additional risk is only 5.2.
Even so, the number of female centenarians is likely to increase every year for the foreseeable future. Official statistics suggest that by 2034, the gap will have narrowed to just two women centenarians for every man.
At least men can console themselves with the fact 100-year-old males are generally healthier than centenarian women.
Fewer get dementia or suffer from chronic conditions such as arthritis, osteoporosis and auto-immune disorders. So, perhaps men may be having the last laugh after all.
Secrets Of The Centenarians: What Is It Like To Live For A Century And Which Of Us Will Survive To Find Out? by John Withington is published by Reaktion Books, price $41.99. To pre-order a copy visit www.mightyape.co.nz.
The average age of patients in the study was just 38, highlighting risks for younger adults.