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Scientists are as obsessed with the question of why the superold survive and thrive as Ponce de Leon was to find the Fountain of Youth. They want to understand why the Japanese islands of Okinawa are home to the world's largest population of centenarians, with almost 600 of its 1.3 million inhabitants living into their second century many of them active and looking decades younger than their actual years. Like weekend visitors on the summer ferry to Martha's Vineyard, scientists and sociologists clog the boats to Sardinia and Nova Scotia, Canada, to see why those craggy locales harbor outsize clusters of the superold. (Gerontologists are not so beguiled by the Russian Caucasus, where exaggerated longevity claims sparked a series of Dannon yogurt commercials 30 years ago.)
As well as studying these populations intensively to unlock their secrets, scientists have also taken a hard look at the very old in the U.S., most notably in the New England Centenarian Study, led by Dr. Thomas Perls, a geriatrician at Boston University, and in a major study under way at the National Institute on Aging. While the very old are happy to offer homespun explanations for their longevity "I never took a drink"; "I drank a shot of whiskey every day" experts are trying to unravel and understand the biological factors that allow some people to reach 100 while others drop off in their 70s or 80s. Researchers are particularly interested in determining which factors allow up to 30% of those who reach 100 to do so in sufficient mental and physical health: a whopping 90% of centenarians, according to Perls, remain functionally independent up to age 92. "It's not 'the older you get, the sicker you get,' but 'the older you get, the healthier you've been,'" he says. "The advantage of living to 100 is not so much how you are at 100 but how you got there."
It's pretty obvious even to nonscientists that how you get there depends partly on the genes you are born with and partly on lifestyle what and how much you eat, where you live and what types of stress and trauma you experience. How much depends on each factor, though, was unknown until Swedish scientists tackled the problem in 1998. They did it by looking at the only set of people who share genes but not lifestyle: identical twins who were separated at birth and reared apart. If genes were most important, you would expect the twins to die at about the same age. In fact, they don't, and the average difference convinced the scientists that only about 20% to 30% of how long we live is genetically determined. The dominant factor is lifestyle.
"You could have Mercedes-Benz genes," says Dr. Bradley Willcox, of the Pacific Health Research Institute in Honolulu, "but if you never change the oil, you are not going to last as long as a Ford Escort that you take good care of. Those who have healthier genes and live healthier lives those guys really survive for a long time."