The Oldest Old
Scientific American
The Oldest Old
People in their late nineties or older are often healthier and more robust than those 20 years younger. Traditional views of aging may need rethinking.
January 1995 Volume 272 Number 1 Pages 70-75
By Thomas T. Perls
In medical school I was taught that the incidence of chronic, disabling disorders, particularly Alzheimer’s disease, increases inexorably with age. I therefore expected that people older than 95 years, often called the oldest old, would be my most debilitated patients. Yet when I became a fellow in geriatrics, I was surprised to find that the oldest old were often the most healthy and agile of the senior people under my care. In fact, the morning I was scheduled to interview a 100-year-old man as part of a research project, he told me I would have to delay my visit. He had seen 19 American presidents take office, and he would be busy that morning voting for the next one.
Such encounters made me wonder if the prevailing view of aging as advancing infirmity was partly wrong. Could it be that many people in their upper nineties enjoy good health and that the oldest old constitute a special–and long-misunderstood–population? Since then, the centenarians I have met have, with few exceptions, reported that their nineties were essentially problem free. As nonagenarians, many were employed, sexually active and enjoyed the outdoors and the arts. They basically carried on as if age were not an issue. And accumulating evidence indicates that a significant portion of the oldest old are indeed healthier than many people in their eighties or early nineties. The common idea that advancing age inevitably leads to extreme deterioration does, indeed, seem to require revision.
Estimated costs of caring for the oldest old in the future might need modification as well. The centenarian population grew by 160 percent in the U.S. during the 1980s. Many demographers predict that 20 million to 40 million people will be aged 85 or older in the year 2040, and 500,000 to four million will be centenarians in 2050. The economic burden of caring for people older than 85 could be vast, especially if a huge percentage of them need special care. Yet it may well be that health bills for the oldest old will be lower than previously expected.
Some of the first evidence supporting my suspicions came from a study on Alzheimer’s disease that I conducted with my mentor, Lewis A. Lipsitz of the Hebrew Rehabilitation Center for Aged in Boston. Surveys have reported that this disorder devastates the mind and ultimately kills about 40 percent of those aged 85 and older. Some investigators believe that close to 50 percent of 90-year-olds have Alzheimer’s disease and that up to 70 percent of centenarians are affected. Yet many of the studies on which these conclusions are based did not include subjects older than 93 years, which casts some doubt on these projections. In 1991 Lipsitz and I undertook a pilot study to see if the occurrence of Alzheimer’s disease at the center, a chronic care hospital, matched the predictions for centenarians. We found that of the 12 residents in their hundreds, only four seemed to have Alzheimer’s disease. This low figure–only 25 percent–was particularly striking considering that residents of such facilities are more likely to be impaired than are their counterparts in the community.
Selective Survival
Our finding suggested that, at least cognitively, the oldest old were indeed in better shape than has usually been assumed. What, we wondered, could explain their good condition? We suspect that the answer to this riddle is that, for whatever reason, some people are particularly resistant to acquiring the disorders that disable and kill most people before age 90. Because of this resistance, they not only outlive others, they do so relatively free of infirmities. In other words, in a kind of survival-of-the-fittest phenomenon, these individuals seem to be selected for long-term survival because they possess traits that enable them to avoid or delay the diseases that commonly accompany aging.
The concept of selective survival was applied, somewhat more narrowly, by demographers in the 1970s to older African-American populations. Researchers reported that although the death rates for blacks were higher than for white Americans up to age 75, the trend reversed after that age. Then, in what some called a crossover phenomenon, whites were more likely to die at a given age than were their African-American counterparts. They speculated that blacks tended to die earlier because many of them were economically disadvantaged and had less access to health care services. Therefore, those who survived represented an unusually vigorous group, able to overcome obstacles that defeated others. Their vigor, in turn, later gave them a survival advantage over the majority of white Americans of similar age.
This selective survival hypothesis may also clarify various other once puzzling findings demonstrating unusually good cognitive and physical health in the oldest old. It seems that men who survive into their late nineties become less and less likely to develop Alzheimer’s disease with each passing year. Moreover, the average man in his late nineties has a more intact mind than the average man in his eighties. These patterns probably emerge because men who are susceptible to Alzheimer’s disease generally die of the condition in their eighties or early nineties. These trends would be explained if the group of men who reach their late nineties consist almost exclusively of individuals who are not susceptible to Alzheimer’s disease and who therefore retain their cognitive abilities indefinitely.
