An international research team has gathered a database of the oldest people in the world - those who lived beyond their 110th birthday, and while searching for these 'supercentenarians' and trying to find accurate documentation of their age, they also documented the personal histories and wisdom of those who long-lived folks.

The result; a book called "Supercentenarians" and  coordinated by the Max Planck Institute for Demographic Research (MPIDR) in Rostock/Germany.

How long can humans live?  Some age researchers say the question is obsolete, with no upper limit to life expectancy in sight. Records are being broken every year and today there is not only a dramatically increasing number of centenarians, but also more and more men and women who live to 110 years old or older - the supercentenarians.

Finding these supercentenarians was no easy task for the demographers, since they could not rely on standard statistical methods. In each country the scientists designed their own strategy of how to identify probable candidates of the super old, and then prove their age by locating official documents that confirmed their date of birth and date of death  - or current age if still living.

But there were challenges. In the late 19th century, when the supercentenarians were born, many countries didn't have a central birth registry and any original documents may have been lost or ruined. So the scientists needed to search through a massive amount of certificates, census lists, death registers and the paper files of universities and health and security administrations to identify supercentenarians.

"Investigating very old age has always been difficult for demographers," says Heiner Maier from the MPIDR. "Science has been plagued by myths and fairy tales." Most claims of modern day Methuselahs appear promising at first glance, but usually turn out to be unverifiable. Entries in the Guinness Book of World Records aren't reliable either; their validation is often based solely on documents provided by the families of those who reached an advanced age and are not independently confirmed by scientists.

They spent the last ten years searching for people who reached the age of 110 or more. Together they found over 600 supercentenarians (in the USA, Canada, Japan, Australia, France, Italy, Spain, Germany, Switzerland, Belgium, the United Kingdom and in the Nordic countries). Of the 600, nearly 20 lived beyond 115.  The new data was used to create the International Database on Longevity (IDL), http://www.supercentenarians.org.

"The IDL is the first reliable record of scientifically verified data about supercentenarians on an international scope", says Maier. "It is the best existing account of mortality beyond the age of 110."

The findings varied between countries. In the United States 341 supercententarians were eventually found (309 women and 32 men), whereas in the much smaller country of Denmark only two women were verified as being over 110. In some cases going through all of the records would have been logistically impossible. In Germany, for instance, the researchers would have had to sort through records of roughly 8000 Residence Registry Offices. Luckily, however, researchers found a much faster method - they asked the Office of the German President for help. The President keeps a directory of residents older than 100 in order to send birthday congratulations. With the list in hand the researchers easily tracked down 17 supercentenarians.

The record holder in longevity is still the French woman Jeanne Calment, who died in 1997 at the age of 122. The book "Supercentenarians" celebrates her life - how she met the painter Vincent van Gogh when she was 13, how she later allowed herself one glass of port and one cigarette a day, and how she liked good food and wine, including cakes and chocolate, which she ate every day. When the demographers James Vaupel and Bernard Jeune, two of the authors of "Supercentenarians," visited her at age 120, she remarked that the most important thing in her long life was that "I had fun. I am having fun."

Chris Mortensen's long life is also detailed in the book. Born in Denmark, he died at 115 in the United States. Still the record holder as the world's oldest living man, at his advanced age he still smoked cigars, and lived as long as the Dutch woman Hendrikje van Andel-Schipper. Despite being born prematurely with a weight of only three pounds, she nevertheless avoided major life-threatening diseases until her nineties, when she was diagnosed with a breast cancer, and ultimately died of stomach cancer. The African American woman Bettie Wilson who died at the age of 115 even survived a gall bladder surgery at age 114. And Elizabeth Bolden, also an African American woman, who was deeply religious and had ten great-great-great grandchildren, was allegedly completely mentally fit and was able to recount all the major details of her life on her 112th birthday.

What is striking is that many of the super old avoided dementia, at least until shortly before they died. Now researchers want to expand the use of the International Database on Longevity (IDL) and use its data to investigate mortality at advanced age and the reasons for an extra long life. But these reasons are still elusive.

So far the only thing for certain is that being a woman is clearly advantageous, since ninety percent of those celebrating their 115th birthday were women. Having ancestors who lived exceptionally long played as little a role as economic background and half of the supercentenarians had no children. It is unclear, however, whether this evidence will remain constant with future supercentenarians. The search for the secret of super old age has only just begun.