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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Why are there so few people over 115 years of age? (One)

Rapid increases in numbers reaching 100, but no change in record lifespan

My Times column on how the world's oldest people are getting younger:

The two oldest men in the world died recently. Jiroemon Kimura, a 116-year-old, died in June in Japan after becoming the oldest man yet recorded. His successor Salustiano Sanchez, aged 112 and born in Spain, died last week in New York State. That leaves just two men in the world known to be over 110, compared with 58 women (19 of whom are Japanese, 20 American). By contrast there are now half a million people over 100, and the number is growing at 7 per cent a year.

For all the continuing improvements in average life expectancy, the maximum age of human beings seems to be stuck. It’s still very difficult even for women to get to 110 and the number of people who reach 115 seems if anything to be falling. According to Professor Stephen Coles, of the Gerontology Research Group at University of California, Los Angeles, your probability of dying each year shoots up to 50 per cent once you reach 110 and 70 per cent at 115.

Female “supercentenarians” — as 110-plus people are called — are a long way off breaking the record for long life. The record, 122, was set by Jeanne-Louise Calment in 1997, and the oldest living person in the world, Misao Okawa, 115 years and 199 days as of today, would have to live another seven years to overtake that: meaning Ms Calment’s record will stand for at least 23 years. Ms Okawa is the only person over 115 alive today, whereas in 1997 there were four.

Japan has more supercentenarians per head of population than other countries, but not as many as thought a few years ago. After an investigation in 2010, about 300 very old people, claiming monthly pensions through their children, were found to be either missing entirely or dead in their beds for decades. These phantoms included several over 110.

The lack of any increase in people living past 110 is surprising. Demographers are so used to rising average longevity all that they might expect to see more of us pushing the boundaries of extreme old age as well. Instead there is an enormous increase in 100-year-olds and not much change in 110-year-olds.

The smidgin of good news for the pension industry, therefore, is that it seems that human lifespan comes with some sort of a sell-by date. In this respect we are not like some creatures — tortoises, sharks, trees — that would apparently go on for ever but for accidents and illnesses.

Professor Coles has done 11 autopsies on supercentenarians and finds that most die of congestive heart failure secondary to “systemic TTR amyloidosis”, a thickening of the blood. The rest tend to inhale food particles and get pneumonia. It is not really clear why women live longer than men; probably something to do with their having a different cocktail of steroid hormones.

Next time you hear some techno-optimist say that the first person to live to 250, or even 1,000, may already have been born, remind them of these numbers. The only way to get a person past the “Calment limit” of (say) 125 will be some sort of genetic engineering. This might prove to be, if not easy, at least fairly routine — in technical terms. Fiddling with just a few genes in worms, fruit flies and mice has enabled scientists to extend their lifespan, sometimes up to sevenfold. One recent study in Lausanne found a 50 per cent reduction in the activity of just three genes on Chromosome 2 increased mouse lifespan by about 250 days, and kept them healthy longer.

Ethically, however, such a step in human beings is unthinkable, since it would mean altering the genes of an unborn child without asking his or her permission. It is hard to imagine any government allowing such an experiment, with a high probability of unexpected consequences, let alone anybody finding a team of scientists prepared to do it. Plus, ethics aside, it is not easy to see where the demand for such a drastic and expensive step would come from. Who would actually want their next child to live past 125, let alone badly enough to go through with it?

All those people who eat wheat germ or special yoghurt or vitamin supplements in the hope of living for ever are probably wasting their time. So too are those who practise “caloric restriction” on the ground that mice live much longer if nearly starved. Such gaunt folk might get to 100 instead of 90, but they are not going to get to 120 by such means.

Exercise, too, is nice, but it’s not going to help at extreme old age. People who walk fast at 75 are more likely to live beyond 85 than those who walk slowly, but cause and effect goes the wrong way: being likely to live longer makes you a faster walker rather than vice versa.

It’s still possible there might be a pharmaceutical way of extending lifespan. The genes that need altering to get flies and worms to live longer are all part of a nutrient-signalling pathway, and a drug that affects this pathway has been shown to extend lifespan in flies. It’s called rapamycin, after Rapa Nui (Easter Island) where it was first found in soil bacteria. Rapamycin’s molecular targets are similar in people and flies, so it might work in people too. It is already used as an anti-cancer agent.

But the latest news is not encouraging, because rapamycin’s side-effects are unattractive: impaired wound healing, insulin insensitivity, impaired immunity, cataracts and testicular degeneration. Dr Linda Partridge, of the Max Planck Institute for the Biology of Ageing in Cologne, says that separating these side-effects from the benefits, and working out when people have to start taking the drug to get any benefit, is the current focus of work on mice.

In the meantime, those of us who were born before the last decade of the 20th century can mostly forget about seeing the 22nd century: there are now just seven people born in the 19th century known to be still alive. We may live much longer on average than our grandparents, but there’s not much chance of breaking records. Just as well when you think about the implications for pensions, healthcare costs and intergenerational equity.