Healthy ageing in the Nun Study: definition and neuropathologic correlates.

BACKGROUND: Although the concept of healthy ageing has stimulated considerable interest, no generally accepted definition has been developed nor has its biological basis been determined. OBJECTIVE: To develop a definition of healthy ageing and investigate its association with longevity and neuropathology. METHODS: Analyses were based on cognitive, physical, and post-mortem assessments from 1991 to 1998 in the Nun Study, a longitudinal study of ageing in participants 75+ years at baseline. We defined three mutually exclusive levels of healthy ageing (excellent, very good, and good) based on measures of global cognitive function, short-term memory, basic and instrumental activities of daily living, and self-rated function. Mortality analyses were based on 636 participants; neuropathologic analyses were restricted to 221 who had died and were autopsied. RESULTS: Only 11% of those meeting criteria for the excellent level of healthy ageing at baseline subsequently died, compared with 24% for the very good, 39% for the good, and 60% for the remaining participants. Survival curves showed significantly greater longevity with higher levels of healthy ageing. The risk of not attaining healthy ageing, adjusted for age, increased two-fold in participants with brain infarcts alone, six-fold in those with Alzheimer neuropathology alone, and more than thirteen-fold in those with both brain infarcts and Alzheimer neuropathology. CONCLUSIONS: The biological validity of our definition of healthy ageing is supported by its strong association with mortality and longevity. Avoiding Alzheimer and stroke neuropathology is critical to the maintenance of healthy ageing, and the presence of both pathologies dramatically decreases the likelihood of healthy ageing.

Early life linguistic ability, late life cognitive function, and neuropathology: findings from the Nun Study.

The relationships between early life variables, cognitive function, and neuropathology were examined in participants in the Nun Study who were between the ages of 75 and 95. Our early life variable was idea density, which is a measure of linguistic ability, derived from autobiographies written at a mean age of 22 years. Six discrete categories of cognitive function, including mild cognitive impairments, were evaluated, using the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) battery of cognitive tests. Neuropathologic data included Braak staging, neurofibrillary tangle and senile plaque counts, brain weight, degree of cerebral atrophy, severity of atherosclerosis, and the presence of brain infarcts. Early-life idea density was significantly related to the categories of late-life cognitive function, including mild cognitive impairments: low idea density was associated with greater impairment. Low idea density also was significantly associated with lower brain weight, higher degree of cerebral atrophy, more severe neurofibrillary pathology, and the likelihood of meeting neuropathologic criteria for Alzheimer's disease.

Alzheimer disease pathology in subjects without dementia in 2 studies of aging: the Nun Study and the Adult Changes in Thought Study.

Individuals with antemortem preservation of cognition who show autopsy evidence of at least moderate Alzheimer disease (AD) pathology suggest the possibility of brain reserve, that is, functional resistance to structural brain damage. This reserve would, however, only be relevant if the pathologic markers correlate well with dementia. Using data from the Nun Study (n = 498) and the Adult Changes in Thought (ACT) Study (n = 323), we show that Braak staging correlates strongly with dementia status. Moreover, participants with severe(Braak stage V-VI) AD pathology who remained not demented represent only 12% (Nun Study) and 8% (ACT study) of nondemented subjects. Comparison of these subjects to those who were demented revealed that the former group was often significantly memory-impaired despite not being classified as demented. Most of these nondemented participants showed only stage V neurofibrillary pathology and frontal tangle counts that were slightly lower than a comparable (Braak stage V) dementia group. In summary, these data indicate that, in individuals with AD-type pathology who do not meet criteria for dementia, neocortical neurofibrillary tangles are somewhat reduced and incipient cognitive decline is present. Our data provide a foundation for helping to define additional factors that may impair, or be protective of, cognition in older adults.

Transitions to mild cognitive impairments, dementia, and death: findings from the Nun Study.

The potential of early interventions for dementia has increased interest in cognitive impairments less severe than dementia. However, predictors of the trajectory from intact cognition to dementia have not yet been clearly identified. The purpose of this study was to determine whether known risk factors for dementia increased the risk of mild cognitive impairments or progression from mild cognitive impairments to dementia. A polytomous logistic regression model was used, with parameters governing transitions within transient states (intact cognition, mild cognitive impairments, global impairment) estimated separately from parameters governing the transition from transient to absorbing state (dementia or death). Analyses were based on seven annual examinations (1991-2002) of 470 Nun Study participants aged > or = 75 years at baseline and living in the United States. Odds of developing dementia increased with age primarily for those with low educational levels. In these women, presence of an apolipoprotein E gene *E4 allele increased the odds more than fourfold by age 95 years. Age, education, and the apolipoprotein E gene were all significantly associated with mild cognitive impairments. Only age, however, was associated with progression to dementia. Thus, risk factors for dementia may operate primarily by predisposing individuals to develop mild cognitive impairments; subsequent progression to dementia then depends on only time and competing mortality.