Centenarians

The characteristics of healthy centenarians suggest that they are not examples of delayed or slow aging. Rather, healthy centenarians have experienced an aging process different from that of the general population. James Vaupel's heterogeneity of frailty hypothesis supports this, showing that very long-lived groups follow different trajectories of aging, compared to short- or average-lived populations. Genetics are likely an important factor in becoming a healthy centenarian. T. T. Perls's group in Boston, among others, has shown that centenarianism clusters in families. Unfortunately, when the association between specific human genes and longevity has been investigated, the results have often been inconsistent. The best candidates are mitochondrial genes; the gene for tyrosine hydroxylase, an enzyme involved in cellular respiration; and possibly the apolipoprotein E, a protein involved in cholesterol metabolism and function. Studies in the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans demonstrate that genes involved in the insulin signaling pathway exert an important effect on longevity.

This may be one of the mechanisms through which caloric restriction promotes longevity. No such effects of the insulin signaling pathway have yet been identified in humans, however. What is shared by these candidate genes is an involvement in gene-environment interactions, allowing an individual to suffer less harm from environmental stressors than others without one of these beneficial genotypes, in keeping with the Inflamm-Aging and Compensatory Adaptation theories. These genes do not seem to slow an aging clock, if such a clock exists in humans. Other investigators wonder if extreme longevity is caused by the absence of genotypes that promote disease; evidence for this is lacking as of 2001.

Women with fewer children seem to live longer. Observational data from humans support this, and studies with nematodes and insects also demonstrate that less fertile individuals live longer. This may be an example of one theory of aging at work, George Williams's Antagonistic Pleiotropy. Antagonistic pleiotropy holds that some genes which may be beneficial (in this case, genes that cause one to be reproductively successful) are harmful later in life, leading to disease or accelerated aging. Conversely, genes that are detrimental early in life (and so make one less successful at reproduction) may be beneficial in late life, promoting longevity. The data from insects support the latter explanation more so than the former.

Good genes are not likely the only reason explaining the achievement of long, healthy lives. A number of childhood factors, including parental literacy, a stable home life, and good childhood health promote longevity. Higher educational achievement and socioeconomic status are beneficial. Not smoking and maintaining a healthy weight are also important.