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What is the nun study?
Later Adulthood (60 and Older)
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The nun study is a fascinating examination of aging and Alzheimer’s disease conducted in a convent for retired nuns in Mankato, Minnesota. Religious orders make marvelous settings for epidemiological research studies (studies of health and disease patterns in whole populations) because of the relatively uniform lifestyle found in these environments. With many potentially complicating variables held constant, such as smoking, alcohol use, quality of health care, and income, it is much easier to have confidence in the research results.
David Snowdon, the study’s lead researcher, began the study in 1991 with a population of 678 nuns. He administered tests of cognitive function and health status. Remarkably, the convent had preserved the essays the nuns wrote upon entering the convent in their teens or early twenties. Finally, the nuns gave their permission for their brains to be autopsied after death. This is critical, as the only way to definitively diagnose Alzheimer’s disease is through brain autopsy.
Although the study is ongoing, several noteworthy findings have already been published. For one, essays written in the nuns’ adolescence and early adulthood gave clues as to who was more likely to develop Alzheimer’s disease later on. The nuns who used more complex grammar and ideas and more positive emotion words were less likely to develop Alzheimer’s disease 60 years later. More educated nuns also had a lower chance of developing Alzheimer’s. From this data alone, however, we cannot distinguish between cause and effect. Do the essays reflect the earliest manifestations of Alzheimer’s or good habits that ultimately protect against the disease?
The autopsy data give clues to this $64,000 question. Although the degree of brain damage due to neurofibrillary tangles and amyloid plaques did correlate with the degree of cognitive decline, it was not a 100 percent correlation. In other words, there were nuns with considerable amounts of brain damage who showed little to no dementia. In fact, 58 percent of the nuns with mild and 32 percent of those with moderate brain pathology did not show memory impairment.
The researchers concluded that there was something known as cognitive reserve that protected against functional deterioration in the face of brain disease. They believed that various factors contributed to cognitive reserve by promoting richer neuronal networks (or enhanced communication between brain cells) and greater cerebrovascular health. Such factors seem to include education, positive mood, mental stimulation, and healthy diet (specifically the vitamin folate). Cerebrovascular health is very important because the presence of strokes dramatically reduced the cognitive performance of nuns with Alzheimer’s disease.