THIS year, the number of pensioners in the UK exceeded the number of minors for the first time in history. That's remarkable in its own right, but the real "population explosion" has been among the oldest of the old - the centenarians. In fact, this is the fastest-growing demographic in much of the developed world. In the UK, their numbers have increased by a factor of 60 since the early 20th century. And their ranks are set to swell even further, thanks to the ageing baby-boomer generation: by 2030 there will be about a million worldwide.
These trends raise social, ethical and economic dilemmas. Are medical advances artificially prolonging life with little regard for the quality of that life? Old age brings an increased risk of chronic disease, disability and dementia, and if growing numbers of elderly people become dependent on state or familial support, society faces skyrocketing costs and commitments. This is the dark cloud outside the silver lining of increasing longevity. Yet researchers who study the oldest old have made a surprising discovery that presents a less bleak vision of the future than many anticipate.
It is becoming clear that people who break through the 90-plus barrier represent a physical elite, markedly different from the elderly who typically die younger than them. Far from gaining a longer burden of disability, their extra years are often healthy ones. They have a remarkable ability to live through, delay or entirely escape a host of diseases that kill off most of their peers. Supercentenarians - people aged 110 or over - are even better examples of ageing gracefully. "As a demographic group, they basically didn't exist in the 1970s or 80s," says Craig Willcox of the Okinawa Centenarian Study in Japan. "They have some sort of genetic booster rocket and they seem to be functioning better for longer periods of time than centenarians." The average supercentenarian had freely gone about their daily life until the age of 105 or so, some five to 10 years longer even than centenarians, who are themselves the physical equivalent of people eight to 10 years their junior. This isn't just good news for the oldest old and for society in general; it also provides clues about how more of us might achieve a long and healthy old age.
One of the most comprehensive studies comes from Denmark. In 1998, Kaare Christensen at the University of Southern Denmark, in Odense, exploited the country's exemplary registries to contact every single one of the 3600 people born in 1905 who was still alive. Assessing their health over the subsequent decade, he found that the proportion of people who managed to remain independent throughout was constantly around one-third of the total: each individual risked becoming more infirm, but the unhealthiest ones passed away at earlier ages, leaving the strongest behind. In 2005, only 166 of the people in Christensen's sample were alive, but one-third of those were still entirely self-sufficient (Proceedings of the National Academy of Sciences, vol 105, p 13274). This is good news from both personal and societal perspectives, for it means that exceptional longevity does not necessarily lead to exceptional levels of disability.
Christensen's optimistic findings are echoed in studies all over the world. In the US, almost all of the 700-plus people recruited to the New England Centenarian Study (NECS) since it began in 1994 had lived independently until the age of 90, and 40 per cent of supercentenarians in the study could still look after themselves. In the UK, Carol Brayne at the University of Cambridge studied 958 people aged over 90 and found that only one-quarter of them were living in institutions or nursing homes. Likewise, research in China reveals that before their deaths, centenarians and nonagenarians spend fewer days ill and bedridden than younger elderly groups, though the end comes quickly when it finally comes.
Distinctive minds
Of course, people can live independently without being entirely healthy, and it is true that most centenarians suffer from some sort of ailment. These range from osteoarthritis - which is almost universal and often omitted from studies - to simple loneliness. Neurodegenerative diseases are common too, with around 70 to 85 per cent of centenarians suffering from some form of dementia. But dementia in this group follows a different pattern to the general population. It is more likely to be vascular dementia or rare neurodegenerative conditions such as Pick's disease or Lewy body disease.
Alzheimer's disease, the most common form of dementia, is relatively rare among centenarians yet, intriguingly, autopsies reveal that the brains of the oldest old, who had shown no outward sign of dementia, are sometimes riddled with the lesions associated with Alzheimer's disease. The basis of this resilience to Alzheimer's is largely unknown. The simple fact is that many people who become centenarians seem able to tolerate damage that would significantly harm less robust individuals, and although many suffer from dementia as death draws near, most remain mentally agile well into their nineties.