Academic journal article Annual Review of Gerontology & Geriatrics

The Familiality of Exceptional Longevity1

Academic journal article Annual Review of Gerontology & Geriatrics

The Familiality of Exceptional Longevity1

Article excerpt

THE NATURE VERSUS NURTURE DEBATE

There is substantial heterogeneity in how people age. Some individuals age relatively quickly and develop age-related illnesses such as heart disease or stroke in their 40s and 50s; others appear to age very slowly and, if they do develop age-related illnesses, it may be toward the end of their very long lives. Within these two extremes are the majority of people, who, at least in industrialized nations, have an average life expectancy in their late 70s. Much of the variation around this average appears to be due to differences in environment, behavior, and stochastic factors. Twin studies have estimated the heritability of longevity to be from 15% to 35% (Gudmundsson, Gudbjartsson, Frigge, Gulcher, & Stefansson, 2000; Herskind et al., 1996; Ljungquist, Berg, Lanke, McClearn, & Pedersen, 1998). It is noteworthy, though, that the oldest subjects in these studies were in their mid- to late 80s, and very few, if any, lived to extreme old age. Thus, twin studies suggest that approximately 25% of the variation in average life expectancy can be explained by genetic variation, and the remainder (about 75%) by variation in environment (Perls & Terry, 2003).

Another approach to the question of the impact of environment and behavior on life expectancy is to study populations with high average life expectancies and to determine how they are different from other groups. Seventh Day Adventists have the highest mean life expectancy, of 88 years, in the United States. Given that the racial, ethnic, and geographic makeup of followers of this faith is heterogeneous, it appears that much of their increased life expectancy, over that of the general population, appears to be due to the healthy behaviors dictated by their religion: frugal vegetarian diet, regular daily exercise, no tobacco or alcohol use, and substantial time devoted to family and church activities (which might play roles in managing stress). Based on the Seventh Day Adventist data, it would seem that most Americans, if they were to emulate the habits of Adventists, should be able to achieve an average life expectancy of 88 years (Fraser & Shavlik, 2001).

What is the degree of contribution of environment, however, to live substantially beyond 88-for example, to 100 and older? The answer to this question is not known; however, as noted below, there is evidence that the genetic contribution to survival to these older ages increases relative to the environmental contribution.

A number of centenarian studies support the possibility of a substantial familial (genetic and exposure factors in common among family members) component to exceptional longevity. Perls and colleagues (2002) analyzed the pedigrees of 444 centenarian families in the United States that included 2,092 siblings of centenarians. Survival was compared to 1900 birth cohort survival data from the U.S. Social security Administration. As shown in Figure 4.1, female siblings had death rates at all ages that were about one-half the national level; male siblings had a similar advantage at most ages, though diminished somewhat during adolescence and young adulthood. The siblings had an average age of death of 76.7 for females and 70.4 for males compared to 58.3 and 51.5 for their respective birth cohorts. Even after accounting for race and education, the net survival advantage of siblings of centenarians was found to be 16 to 17 years greater than the general population.

Relative survival probabilities for these siblings increased markedly at older ages, reflecting the cumulative effect of their mortality advantage throughout life (see Table 4.1). Compared to the U.S. 1900 birth cohort, male siblings of centenarians were 17 times as likely to attain age 100, while female siblings were 8 times as likely. The analysis of death rates indicates that the siblings' mortality advantage does not grow as they get older. Rather, their relative probability of survival is a cumulative measure and reflects their life-long advantage over the general population born around the same time. …

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