How to live for ever

JEANNE CALMENT (pictured), who lived for 122 years and 164 days (longer than any other person), said the secret to her longevity was a diet rich in olive oil, port wine and chocolate. She smoked until the age of 117. Alexander Imich, who was the oldest living man (111) until he died in June, did not have a secret. 

Asked how he lived so long, he replied, "I don’t know, I simply didn’t die earlier." Scientists are looking for more plausible and definitive reasons why some people live much longer than others. Many think the genes of centenarians like Calment and Imich hold the key. And some believe that their research might one day provide a positive answer to the question that has fascinated man since at least the time of Herodotus: is it possible for humans to live for ever?

There are a number of biological components involved in the process of ageing. These cause the body to slowly degrade at the cellular level. Old age is also a leading risk factor for many common illnesses, such as cancer and heart disease. Tackling ageing, therefore, is seen as a way to combat many diseases at once. This is the motivation behind Google's anti-ageing startup called Calico, which was founded last year and is led by Art Levinson, the former head of Genentech, a pioneer of the biotechnology industry. Craig Venter, a geneticist who was instrumental in the sequencing of the human genome, created a similar company earlier this year. The primary goal of these and other efforts is not necessarily to extend humans' lifespan, but rather their healthspan, or the number of years lived in good health. Many scientists, though, believe that any effort to slow or stop the progression of age-related diseases must deal with the cellular damage involved in ageing—so longer life is an inevitable and welcome byproduct.

These newer outfits and much anti-ageing research over the past decade have focused on genes. The chances of a person living to 80 are based mostly on behaviour—don't smoke, eat well and exercise—but the chances of living beyond that are based largely on genetics. So scientists are looking for the "protective genes" that slow cellular decline and ward off diseases in people like Calment and Imich. If researchers can find them it is hoped that pharmaceutical firms might create drugs that mimic their effects in people otherwise likely to achieve normal lifespans. That might only get them to Calment's age, which some scientists believe is the absolute limit of human longevity. Others think that to go further the body must be treated like a machine in need of regular repair and replacement parts. Regenerative medicine offers some hope in this regard. 

Scientists are using stem cells to grow human replacement parts, like tissues and organs. In theory, a person could keep going back to the shop for new parts, so long as his brain remained intact. Scientists even talk about treating diseases that ravage the brain, like Alzheimer's and Parkinson's, with replacement nerve cells.

Optimists, like Aubrey de Grey, a provocative anti-ageing researcher in England, believe that technology will allow people alive today to live well beyond Calmet's 122 years. Most others believe that such progress is some way off. A more realistic hope is that anti-ageing research will lead to lower health-care costs. One of the characteristics of the very old is that they tend to be healthy right up until their deaths. 

They therefore cost health-care systems less than most old people, especially those suffering from chronic diseases. Scientists talk of a "longevity dividend" that might be achieved by compressing the period of ill health at the end of life for everyone. This would at least address the paradox of the quest for eternal life: people want to live for ever, but they don't want to grow old.