Stephanie Cosentino of Columbia University in New York and colleagues examined the cross-sectional study included a total of 1,870 individuals -- 1,510 family members and 360 spouse controls -- recruited through the Long Life Family Study.
The main outcome measure was the prevalence of cognitive impairment based on a diagnostic algorithm validated using the National Alzheimer's Coordinating Center data.
The study, published in the journal Neurology, found the cognitive algorithm classified 38.5 percent as having cognitive impairment consistent with Alzheimer's disease.
Long Life Family Study subjects had a slightly but not statistically significant reduced risk of cognitive impairment compared with spouse controls, whereas Long Life Family Study sons and daughters had a reduced risk of cognitive impairment.
"Overall, our results appear to be consistent with a delayed onset of disease in long-lived families, such that individuals who are part of exceptionally long-lived families are protected but not later in life," the researchers concluded.