Reaching a 100th birthday will soon become a commonplace event. But the centenarians of the new millennium will not be the chronic sick and long-stayers of managers worst nightmares, writes Jenny Bryan

Within the next 12 months, more than 8,000 people in the UK will be able to boast of having reached the venerable age of 100. Turn back the clock just 50 years and scarcely 400 could have made the same claim. Spin the clock hands forward to, say, 2030, and the number will have soared above 50,000.

The days when we could only hope for three-score years and 10 are long gone. Life-expectancy for British women currently stands at nearly 79, and at just over 74 for men. At the beginning of the last century it was less than 50.

Thanks to a sprightly French woman, Jeanne Calment, who died in 1997, the human lifespan (equivalent to the greatest age ever recorded) has extended to 122 years.

The reasons why a small proportion of people live so much longer than everyone else have fascinated researchers for decades.

Countless older people have been wheeled in front of TV cameras in order to reveal the secrets of their longevity, from a daily glass of whisky to a happy marriage.

But cast aside the elixirs of eternal life and there are two common threads - an inherited tendency to longevity and good health through middle and old age when you should be succumbing to heart disease and cancer .

Anyone who gets to 100 is going to be a survivor . They've avoided heart disease, strokes and cancer and, although they're frail, they are just not susceptible to the common risk factors. In effect they've become immortal, explains Professor Shah Ebrahim, who specialises in the epidemiology of ageing in the department of social medicine at Bristol University.

Get past the age of 95, he explains, and you'll probably have a clear run to the royal birthday card. Until that age, an individuals risk of dying within 12 months increases sharply from about 1 per cent at the age of 60 to about 50 per cent in their early nineties. But, at around the age of 95, this risk flattens out. Instead of rising inexorably to 100 per cent it sticks at around 50 per cent.

What finally sends centenarians skywards is usually a minor accident. A fall reduces their mobility, leaving them chair or bed-bound, taking away their appetite, reducing their resistance to infection.

So if we wrapped them in cotton wool when they reach 100, could life's survivors live for ever?

In theory yes, but in reality no, says Professor Ebrahim. One of the reasons people become survivors is that they stay independent and remain mentally and physically stimulated. If we reduce their risk of an accident by stopping them from going shopping or out to the pub, they'll also lose the mobility and the mental stimulation which have kept them going so long.

The good news for healthcare planners in the new millennium is that centenarians are not expensive to run.

The events that trigger their demise are telescoped into a few years rather than filling thick medical files from middle age onwards. Recent US experience showed that, even at 92, people who went on to reach 100 were taking only 1.6 medicines for a mean 2.6 chronic diseases.

1In their early 90s, they averaged 0.3 admissions to hospital a year and, at the time of the study, when all participants were over 100, the most recent admission to hospital was, on average, nearly four years earlier, lasting an average of seven days.

Hardly the sort of long-stay, chronically sick elderly people who worry budget-holders. Nonetheless, some experts are concerned at the lack of appropriate care available to the elderly population from which future centenarians will emerge. Because of our shifting demography , we really do need a revolution in the whole Still going strong: a century and not out of medicine. We all need to become gerontologists, explains Professor Elaine Murphy , chair of East London and the City health authority and former head of psychogeriatrics at Guy s Hospital, London.

She points out that, in the past five years alone, the number of men over 85 attending hospital outpatients has almost doubled and the proportion of hospital beds occupied by the over-75s has jumped from 30 up to 40 per cent.

Hospital services are now geared to fast admission and discharge, something which isn t necessarily suited to the elderly.

Much more ef fort needs to go into creating teams of GPs, nurses, therapists and social workers who can care for the elderly in the community rather than in hospital, says Professor Murphy .

Both she and Professor Ebrahim point to the growing shortage of broad-based, general geriatricians.

The elderly patient who has had a fall and is confused could have all sorts of things wrong with them and we need generalists to deal with the initial presentation. But we are creating so many specialties and sub-specialties that we will end up with no-one to do the basic assessment, says Professor Ebrahim.

The promise of new treatments for dementia is creating one such specialty and drawing bright young talent to a previously neglected area. But for future centenarians who traditionally keep their mental faculties long after others have lost them, the need is for health and social care that can sort out their occasional funny turn and, most importantly , keep them motivated and independent.