The quest to live longer is one of humanity's oldest dreams and three isolated communities seem to have stumbled across the answer. So what can they teach us about a longer life?
Something remarkable links the remote Japanese island of Okinawa, the small Sardinian mountain town of Ovodda and Loma Linda in the US. People live longer in these three places than anywhere else on earth.
At an age when the average Briton is predicted to die - 77 years for men and 81 for women - inhabitants of these three places are looking forward to many more years of good health. Often they're still working in jobs as demanding as heart surgery. 
Okinawa has a population of one million and of those 900 are centenarians, four times higher than the average in Britain or America. Even more remarkably, Ovodda is the only region in the world where as many men as women live to be 100 years of age, bucking the global trend.
But what is even more intriguing is that each community is distinct from the others and raises a different theory as to why residents live longer. In all three communities scientists have dedicated themselves to trying to uncover these unique secrets. So what can we learn from the towns where people live the longest?
There is one remarkable scientific fact that sets Okinawans apart from the rest of us, they actually age more slowly than almost anyone else on earth.
"The calendar may say they're 70 but their body says they're 50," says Bradley Willcox, a scientist researching the extraordinary phenomenon. "The most impressive part of it is that a good lot of them are healthy until the very end."
Finding the cause of their exceptional longevity is not simple but the spotlight has fallen on one hormone - DHEA. It's a precursor of both oestrogen and testosterone and produced in the adrenal glands.
While scientists don't know what it does, they do know the hormone decreases with age and levels decline at a much slower rate among the Okinawans.
Explanations for this mostly centre around the dinner table. The Okinawans not only eat more tofu and soya products than any other population in the world, their diet also includes a vast range of different vegetables and fruit all rich in anti-oxidants. Scientists refer to it as a rainbow diet. 
But it's what they don't eat that may be at the heart of their exceptionally long lives.
The Okinawan's most significant cultural tradition is known as hara hachi bu, which translated means eat until you're only 80% full.
In a typical day they only consume around 1,200 calories, about 20% less than most people in the UK. Culturally it is a million miles from attitudes in a lot of Western societies, where all-you-can-eat meal deals are offered in restaurants on most high streets.
Scientists call it caloric restriction, but don't entirely understand why it works. They think it sends a signal to the body that there is going to be a impending famine, sending it into a protective, self-preservation mode.
In stark contrast to Okinawans, the residents of Ovodda don't count calories and meat is very firmly on the menu, while tofu and soya are not.
But this small town of just over 1,700 residents boasts five centenarians and, even more remarkably, as many men live to 100 as women.
The benefits of a Mediterranean diet are well known, but this still does not account for the number in Ovodda and other parts of Sardinia. It's even the case that Sardinians who emigrated at 20, 30 or 40 years of age still manage to reach 100, say researchers.
Over the years Professor Luca Deiana has tested every single Sardinian centenarian and has come up with a surprising theory about why there are so many.
For hundreds of years families in Ovodda have lived in relative isolation from the rest of the world, marrying into each others' families. In fact most people living in the town today are descended from only a few original settlers. 
"Marriage among relatives is not the rule but there are some cases of this taking place," says Professor Deiana.
"From a genetic point of view when this happens there's a higher probability of having genetic diseases, but also of having positive results like centenarians."
In Ovodda, this interbreeding actually seems to have enabled people to live longer. The limited gene pool has provided a unique opportunity to discover specific genes that are associated with long life. Professor Deiana has detected a number of unusual genetic characteristics that seem to link the centenarians of Ovodda.
"One particular gene on the X chromosome seems to be faulty, failing to produce an enzyme known as G6PD. This can often have a negative impact on health, but in Ovodda it may well have had a positive effect."
The role G6PD may play in living longer is now being researched further, but the professor is convinced the genetic elixir of life lies with the families of Ovodda.
In Loma Linda, California, one community is proving anyone can increase their chances of living a longer, healthier life. The extraordinary longevity of residents may not have anything to do with genes.
The community has discovered a secret that's much easier to find than any gene. Its effect is so powerful that it enables them to live longer than anyone else in the US.
For many of those living in Loma Lindo long life is a matter of faith. A significant number of people in the town are Seventh Day Adventist, a religion whose members live between five and 10 years longer than fellow citizens. 
This can be partly explained by the fact Adventists don't drink or smoke and many stick to a vegetarian diet the church advises. But not all members do and even they live significantly longer than average.
"It does certainly raise the question if there's something about spiritual life that also has an impact on longer life," says Dr Gary Fraser, who is researching the community.
"At this moment we don't really know that but there's been one interesting fact that's been known now for 20 or 30 years and that is that people that go to church regularly - whatever faith they have - live longer and there's no question about that."
It seems that regular churchgoers have significantly lower levels of stress hormones and so may be better equipped to cope with the challenges in life, say scientists.
"Religion and connection to something higher than oneself, connection to the sacred, connection to a tight-knit religious community allows you to modulate your reactions and your emotions to believe there is a broader purpose," says Dr Kerry Morton, who is involved in a longer-term study on Adventist health.
