Some degree of human longevity is genetic rather than the result of environment and lifestyle choice; researchers have guessed that perhaps 25% of variations are genetic, but this is hardly a firm number. It appears to be the case that survival at extreme old age is more influenced by genetic variations than it is in early old age, for example. Given that some predisposition to longevity is thus inherited, it isn't surprising to find that risk levels for specific conditions of aging also correlate with familial longevity:
Based on comparisons of people in their 90s, their spouses, siblings, children and their children's spouses, researchers found that the offspring of people with exceptional longevity were about 40 percent less likely than peers to be cognitively impaired between ages 65 and 79. "It's not necessarily that these individuals never become cognitively impaired, but what it seems like is that there is a delayed onset of cognitive impairment."
For the new study, the researchers used data on cognitive impairment from 1,870 people who are part of the Long Life Family Study, which includes volunteer participants in New York, Massachusetts, Pennsylvania and Denmark. The study included 1,510 people with a family history of longevity and 360 of their spouses, but for this study, researchers used information on just the volunteers who were 89 years old or older when they were recruited.
Overall, the researchers found that about 6 percent of the volunteers' children were cognitively impaired between ages 65 and 79 years old, compared to 13 percent of their spouses and about 11 percent of their cousins. Among the study's long-lived older generation, participants were just as likely to be cognitively impaired by about age 90 as their siblings or spouses. "These families seem relatively protected, but once they reach extreme old age - say after 90 (years old) - their rates of cognitive impairment become comparable."