Researchers suspect that, as the ultimate survivors, centenarians have the potential to help scientists uncover biological secrets such as the key to disease-free aging; settle debates like whether there is a natural limit to the human lifespan; and even yield new therapies for such chronic ailments as heart disease, cancer and dementia, which also afflict those much younger.
Many researchers believe that centenarians are an exclusively modern phenomenon, according to Jean-Marie Robine, a demographer, epidemiologist and senior fellow at the National Institute of Health and Medical Research in France. He, Bernard Jeune and James Vaupel (both from the Max Planck Institute at Odense University in Denmark) have posited that there were no true centenarians before 1800. Every pre-1800 case of supposed centenarianism they have investigated has turned out to be either provably false or impossible to confirm, Robine said.
Robine observed that the rising population of centenarians in France--from an estimated 200 in 1950 to a peak of 10,000 today--are proving that old notions of longevity are wrong. The new observed length of life contradicts a commonly believed idea, first espoused in 1749 by George-Louis Leclerc, the Comte de Buffon, that there is a natural limit to the human lifespan.
"If we believe that there were no centenarians before 1800, the lifespans that we are seeing today, such as Mme. Jeanne Calment who lived to age 122, are even more surprising," Robine said. "If you go back into literature about human longevity, you find that the maximum is 110 and 112, and the authors keep increasing the number. After Jeanne Calment lived to 122, for two or three years no one proposed a new figure. Now you can see that there are new propositions of 125 and 130 as the maximum, but there is still no scientific basis to these propositions."
NEW ENGLAND STUDY
As the lid blows off the human lifespan, notes Harvard Medical School geriatrician Thomas T. Perls, evidence grows that some of our most axiomatic assumptions about aging are flawed and that aging and disease, although often related, are clearly separate phenomena. Perls, Harvard geriatric neuropsychologist Margery Hutter Silver and I coauthored Living to 100: Lessons in Living to Your Maximum Potential at Any Age (New York City: Basic Books, 1999).
In their New England Centenarian Study, Perls and Silver conducted detailed testing of centenarians' mental and physical status. The onset of illnesses classically associated with aging, such as heart disease, cancer and dementia, appeared to be significantly delayed--appearing only in their 90s--among those who eventually celebrated their 100th birthdays. Some centenarians, they observed, reach 100 without suffering any aging-associated diseases, and may die in accidents or from infectious diseases without showing any symptoms of Alzheimer's disease.
"When I was in medical school," Perls commented, "one message was constantly drummed into us: 'The older you get, the sicker you get.' What we've found from observing centenarians is 'The older you get, the healthier you've been.' Centenarians are a model of relatively disease-free aging and offer a route to understanding how we can age with significantly less disease burden."
By studying the siblings and families of centenarians, Perls has determined that extreme longevity--and the tendency to remain disease-free for the majority of one's life--is probably controlled by just a very few genes, perhaps less than 10. He and other Boston researchers, including Lewis Kunkel of Children's Hospital and Eric Lander of the Whitehead Institute, are currently searching for these genes, and results may be available soon.
"The presence of just a small number of genes having a great influence on aging means that there could be effective ways to control aging," Perls said. "Just as we began learning how to delay or avoid heart disease two or three decades ago, we could be at the point of learning similar lessons about aging."
Nir Barzilai, an associate professor of medicine at Albert Einstein College of Medicine, New York City, hopes to have similar results from his study of centenarian Ashkenazi Jews in this country and Israel. Barzilai and Perls hope that finding the genes that control aging may result in the development of drugs or practices that will delay aging and the diseases commonly associated with it.
"Many people think I'm looking for the Fountain of Youth, and that's precisely what I'm not doing," Barzilai stressed. "I have no intention of maximizing humans' lifespans as some other research studies do with worms. The point is to try to find how these genes protect individuals from disease and see if we can use [this knowledge] to help other people."
John F. Lauerman is a health writer based in Brookline, Mass., and coauthor of Living to 100 (see above). For more information about the book and its authors' "life expectancy calculator" visit www.livingto100.com.
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