Centenarians

The bulk of centenarians are women. At any age women have a greater life expectancy than men, and by the time one reaches one hundred, the sex ratio is four women to one man. The one place where this does not seem to be the case is the island of Sardinia, where the ratio is two women to one man. This finding is not yet explained, though the fact that Sardinia has had a relatively closed gene pool for thousands of years raises the possibility that Sardinians carry a sex-specific gene that promotes longevity. Among supercentenarians the sex ratio is five women to one man.

Figure 2 Percentage of centenarians functioning independently over the course of the previous 10 years in their lives. SOURCE: Hitt, R.; Young-Xu, Y.; Silver, M.; Perls, T. ``Centenarians: The Older You Get, The Healthier You Have Been.'' Lancet 354 (1999): 652.

Many centenarians continue to function independently. In the New England Centenarian Study, 40 percent of centenarians were completely independent, and close to 90 percent had been independent ten years earlier, at an average age of ninety-two (see figure 2). In the Italian Centenarian Studies, with close to four hundred subjects, about 25 percent were in perfect health. Another 30 percent were in relatively good health. Interestingly, males who live this long do very well compared to females, making up 30 percent of those in perfect health but only 15 percent of those in poor health.

Centenarians escape many of the common diseases associated with aging. Cancer, heart disease, and diabetes are all less common in centenarians than in seventy- or eighty-year-olds. One important aging-related disease is dementia. The incidence and prevalence of dementia increase exponentially with aging but, as with other diseases, many centenarians do not suffer from dementia. Between 40 percent and 60 percent of subjects in studies from Europe, the United States, and Japan were diagnosed with dementia. The others were cognitively normal. When brain tissue from centenarians without dementia is examined, it often does not show any of the changes typically associated with Alzheimer's disease or stroke. These data show that common aging-related diseases are not inevitable, and it is possible to live into very late life and remain well. Serenity may be a personality characteristic of centenarians. Several of the studies found that many of their subjects were easygoing and relaxed.

The metabolic state of centenarians is paradoxical. Several groups have found that healthy, functional centenarians have metabolic characteristics that are commonly associated with disease, such as unfavorable cholesterol profiles, with high concentrations of harmful substances such as triglycerides and low-density lipoprotein cholesterol (LDL-C) and low concentrations of the beneficial high-density lipoprotein cholesterol (HDL-C). They also have high levels of proinflammatory cytokines such as interleukin-6, and high levels of prothrombotic substances. Several theories try to explain these paradoxical findings. Among them is Claudio Franceschi and colleagues' Inflamm-Aging. Inflamm-Aging hypothesizes that aging is due to environmental stresses, particularly inflammatory ones, and that people who live very long, healthy lives may have one, or both, of two characteristics. Either they avoid these stresses, which is unlikely, or, more likely, they have a particular mix of genes (their genotype) that is robust and can minimize the negative effects of the inflammation. A similar theory is François Schächter's Compensatory Adaptation, which suggests that centenarians have a genotype which allows them to better resist internal or external stresses that would cause disease in an individual with a less favorable genotype.