He believes that a gene or genes are responsible for the extremely high HDL levels, which may have helped the very old people in his studies maintain their sharp minds and clear memories. He says their high HDL levels, which are presumably controlled by genes, might protect them from heart disease; HDL clears fat from coronary arteries, among other things.
Other researchers say that longevity-enabling genes might protect people in much the same manner as caloric restriction, the only treatment or dietary strategy shown experimentally to extend life. Studies with laboratory rats have found that those fed an extremely low-calorie diet live at least 33 percent longer than rats that eat their fill. The restricted animals also seem to avoid ailments connected with aging, such as diabetes, hypertension, cataracts and cancer. Another possibility is that longevity-enabling genes limit the activities of free radicals—unpaired electrons known to corrode human tissue. Medical researchers have suggested that free radicals spur atherosclerosis and Alzheimer’s disease, for instance. “Free radicals are a key mechanism in aging,” Perls says. “I wouldn’t be surprised if something to do with freeradical damage pops up in our genetic studies.”
If Macknight receives funding to pursue the research, he and his associates plan to interview Nova Scotian centenarians about their histories as well as examine them and draw blood samples for genetic analysis. He hopes to work with Perls to compare the Nova Scotians’ genetic material to that from Perls’ New England subjects, with an eye for similarities or differences that might betray the presence of longevity-enabling genes.
Like all students of the extremely old, MacKnight is interested in their habits and practices. “We’re trying to look at frailty,” MacKnight says, “or, what makes some 100-year-old people seem like they’re 60 and some seem like they’re 150. What are the differences between those who live in their own homes and cook their own breakfast and those who are blind and deaf and mostly demented and bed-bound? And can we develop some kind of intervention for people in their 50s and 60s to keep them from becoming frail?”
Not all centenarians—not even all of those in Nova Scotia— seem as young as Betty Cooper. And though it could be that the difference between the frail and the strong is determined largely by genes, researchers say it is also true that some people who reach 100 in fine shape have been especially prudent. Among centenarians, smoking and obesity are rare. Other qualities that are common to many centenarians include staying mentally engaged, having a measure of financial security (though not necessarily wealth) and remaining involved with loved ones. And though healthy nonagenarians and centenarians often say they’ve led physically active lives—“I did a lot of hard labor,” says 90-year-old Arthur Hebb, of Lunenburg County, who eagerly reads the newspaper every day—Perls and other researchers haven’t definitively answered that question.