"Centenarians tend to be independent, assertive, funny, and gregarious," says Boston University Medical School geriatrician Thomas T. Perls, who at 43 has probably met more people over the age of 100 than anybody else. "They also seem to manage stress very well, which makes sense, since we know that not handling stress predisposes you to cardiovascular disease and high blood pressure."

During a fellowship in geriatrics at Harvard Medical School in the early 1990s, Perls took care of 40 patients at Boston's Hebrew Rehabilitation Center for the Aged. Two of his healthiest patients, who looked as if they were in their seventies, were actually over 100 years old. "They were in really terrific shape," he says. "It was so different from what I expected! This sparked my interest."

As a result, Perls founded the New England Centenarian Study in 1994, becoming one of only a few researchers studying the very old at that time. He started out by looking for people over 100 in eight towns around Boston, using census records, voter registration files, and the media. Later, he expanded the study by adding centenarians from all over the United States. Now it includes 1,600 centenarians and 500 of their children. About 20 percent of the centenarian women in his study had given birth after the age of 40, Perls found, compared to a national average of only 3 percent of mothers. "It showed that these women were aging very slowly," he says.

He also studied the centenarians' siblings and concluded that their chances of living to their early nineties were four times greater than average. More recently, Perls examined the centenarians' children. At the age of 70, he found, they had a 24 percent reduction in mortality compared to the general population, as well as about a 60 percent reduction in the risk of heart disease, hypertension, and diabetes.

More than 90 percent of the centenarians had been in good health and completely independent until their early to mid-90s, Perls says. "They lived the vast majority of their lives with good function," he emphasizes. "So it's not a matter of 'the older you get, the sicker you get' but rather 'the older you get, the healthier you've been.' This is a different way of thinking about aging."

By the time people reach the century mark, however, the healthy ones are in the minority. "We found that 25 percent of the centenarians were doing well, but the remaining 75 percent had mild to severe impairment," Perls reports. "In the end, they die of cardiovascular disease or something that's related to frailty, such as pneumonia."

This fits in well with the theories of Leonard Hayflick, of the University of California, San Francisco, who showed in 1961 that there are limits to the number of times a normal human cell can divide. Even under the most favorable conditions, he said, noncancerous human cells die after about 50 cell divisions (this is now called the "Hayflick limit"). Eliminating the leading causes of death in old age—cardiovascular diseases, stroke, and cancer—"will only result in an increase of about 15 years in human life expectancy," Hayflick declared in the November 9, 2000, issue of Nature. Although these 15 years would be a great gift, assuming that people remained healthy during that time, nothing could stop "the inevitable increase in errors and disorders in the cells of vital organs" that results from age, he pointed out. Even the cells' repair processes would become disordered, leading to extreme vulnerability and death.

Then would it be a good thing for more people to live to 100? "Absolutely," says Perls. "Centenarians are sentinels of the health of older people. Our goal is not to get a bunch of individuals to be 120 or 130, but to discover which genes are most protective and then use this information to get a majority of people living almost all their lives in good health, as centenarians generally do."

—Maya Pines

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Reprinted from the HHMI Bulletin,
Spring 2004, pages 12-17.
©2004 Howard Hughes Medical Institute