BETHESDA- A long-term study of nuns is providing valuable new clues to the nature of aging and Alzheimer's disease.

The Nun Study, conducted under the auspices of National Institute on Aging, is the largest long-term investigation of a brain donor population ever conducted. The study began in 1990 and includes 3,926 members of the School Sisters of Notre Dame congregation born between 1886 and 1916, the majority of whom joined the order at about age 20. The study protocol involved ongoing assessments of the mental and physical functioning and activities of daily living of the living nuns and autopsy studies of the nuns who died during the study.

Thirty-seven percent of 94 autopsies showed neuropathologically-confirmed Alzheimer's disease. The autopsies revealed that the hallmark pathological changes characteristics of Alzheimer's disease (neurofibrillary plaques and tangles) tended to increase in density among those between ages 75 and 89, and to decrease thereafter.

This is the first study to involve enough people over the age of 85 to allow researchers to determine whether the incidence of Alzheimer's disease continues to rise with age, or levels off at some point. The finding that the prevalence of Alzheimer's disease at death peaks at ages 85 and 89, and declines after age 90 lends support to the notion that Alzheimer's disease is not an inevitable consequence of biologic aging.

"If Alzheimer's is not a disorder of aging, but a distinct disease that only affects a minority of the elderly, then examination of its pathophysiology will improve our understanding of its cause, prevention and treatment. Additional follow-up of the nuns participating in this study will enable us to further test the relationship between brain lesions and behavior in autopsies of younger nuns, and for behavior assessed years before death," says lead investigator Dr. David A. Snowdon at the Sanders-Brown Center on Aging, University of Kentucky, Lexington.

Previous studies of Alzheimer's disease conducted in China and elsewhere have suggested that early education may play a role in preventing or delaying the onset of Alzheimer's disease. The Nun Study research team conducted an analysis of archival information and questionnaire data to evaluate this possibility. The analysis considered the early and mid-life experiences of the nuns; their autobiographies, school transcripts, and health records.

"Because of the relatively homogeneous adult lifestyle of the sisters in the study, our findings are not confounded by factors such as smoking and alcohol use, reproductive history, marital status, living arrangements, income, or social isolation that tend to be found in other adult populations," says Snowdon.

The data suggests that the more highly educated sisters lived about four years longer with better mental and physical functioning than the sisters who had less than a bachelor's degree. In fact, the less educated sisters had twice the mortality rates of the more educated nuns.

"We are substituting education for intellectual capacity," says Snowdon, "and since the nuns' lifestyles are so similar, we concluded that the findings about education were not so much linked to poor circumstances in adult life, as to something that occurred in youth. We now believe that factor is mental capacity--cognitive ability--and that it is a powerful predictor of Alzheimer's disease in later life," he explains.

Snowdon has another working hypothesis, not based on scientific fact but one in which he has faith nonetheless. "The sisters live so long because they pursue an active physical, social and intellectual life," he says. "Over time, they are giving us valuable clues about the biological advantages of their experience."

SOURCE: National Institutes of Health

Transmitted: 95-05-07 22:20:37 EDT

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