For more than three decades, a group of Catholic sisters quietly reshaped what scientists understand about aging, memory loss and Alzheimer's disease. The Nun Study, a National Aging project that began in 1990 with 678 Sisters of Notre Dame, produced results that continue to guide dementia research today, even though every sister who participated has died.
Their contribution is important now because researchers are still publishing the information they left behind. By 2025, Alzheimer's & Dementia, The Journal of the Alzheimer's Association published a scientific review summarizing decades of findings, calling the project “the landmark long-term study of aging and dementia.” With more than 600 brain autopsies completed and an extraordinary archive of early life records, the research's impact extends far beyond the walls of the monasteries where it began.
How the Nun Study Began and Why Researchers Choose Catholic Sisters
David SnowdonPh.D., launched a pilot in 1986 with the School Sisters of Notre Dame (SSND) to look at the relationship between education and aging-related disorders. She expanded that project into a comprehensive Nun Study in 1990, enrolling 678 sisters from SSND communities across America. Most of the participants were between the ages of 75 and 102 at enrollment. Of the 1,027 eligible sisters, 678, about 66 percent, agreed to participate and commit to annual tests of memory, language, thinking, physical health and daily functioning.
The sisters were unusually important researchers because their adult lives looked so similar. About 85 percent had earned at least a bachelor's degree, and 89 percent had worked as teachers. They share comparable housing, nutrition, health care, income and social networks, variables that often include muddled disease research.
“In general, it is difficult to identify what causes some people to develop dementia while others remain healthy because people can have a very different lifestyle, environment and biology, some smoke, some don't smoke, some have received better health care than others, some may have a better genetic influence on diseases,” Kyra Clarkea medical student at UT Health San Antonio and one of the authors of the review, said, via EWTN News.
“But Catholic sisters from the same order share the same place in most of their adult lives, with the same marriage history and daily routines,” he said. “It is difficult to find a population of people who live in a consistent and comparable way. This makes it easier to find out which factors increase or decrease the risk of dementia.”
Brain Contributions to Alzheimer's and Dementia Revealed
Brain donation was a requirement to join the study. Ultimately, 98 percent of the participants had brain autopsies, and more than 600 autopsies were completed, one of the largest collections of brain tissue ever assembled for Alzheimer's research. Neuropathologists conducting the experiments were blinded to the participants' cognitive test results, allowing direct comparisons between brain changes and cognitive and memory abilities recorded during life.
The researchers also drew on medical records, academic transcripts, autobiographies the sisters had written when they were young and genetic information from blood or tissue samples. The results changed the field in two ways. Some sisters had extensive Alzheimer's-related changes in their brains, including amyloid plaques and neurofibrillary tangles, yet never developed dementia in life. And early-life cognitive ability, as measured by those autobiographies and school records, was associated with better cognitive outcomes decades later.
Together, those results helped establish the concept of memory retention, the idea that lifelong cognitive engagement may help some people retain memory and thinking even when their brains show serious disease. The work also showed that multiple brain diseases are common in older adults and that those overlapping diseases raise the possibility of dementia.
Findings from the Nun Study on Healthy Eating, Folate and Brain Health
The research team also examined how dietary and nutrient levels are linked to brain aging. Sisters with low blood folate, known as vitamin B9, tend to show greater brain shrinkage and poorer cognitive function than those with higher levels. Low folate concentrations, especially along with high homocysteine , were associated with a higher likelihood of developing Alzheimer's disease and cognitive impairment.
The findings did not prove that folic acid prevents dementia. But they suggest that maintaining adequate folate status may be one part of healthy brain aging, a piece of a bigger picture that includes education, cognitive stimulation and existing health conditions.
“Nun's research really emphasized that maintaining mental health is a lifelong task and emphasized the importance of education and mental stimulation in reducing the risk of dementia,” Clarke said.
Why Nun Research Is Still Shaping Dementia Research Today
Although there are no living sisters left in the study for psychiatric diagnosis, work on neuropathy continues. The School Sisters of Notre Dame notes on their website that “the sisters involved continue to impact Alzheimer's research through their brain donation.” Margaret Flanaganwho directs ongoing research at UT Health, has a personal connection to the church, as several family members attended Chicago's Academy of Our Lady, a school run by SSND. Researchers still meet regularly with SSND representatives to share updates.
Influence on the wider scientific community was important from the beginning. “The Nun Course has certainly been pioneering,” he said Dr. Richard Suzmanchief of demography and population epidemiology at the National Institute on Aging, per The New York Times. “It helped change the way people think about aging and Alzheimer's disease.”
Dr. Robert P. Friedlandprofessor of neuroscience at Case Western Reserve University, pointed out what makes this design so unusual. “I think the Nun Study is very important because it uses data from people before the onset of illness,” he said. “So we know from the research of Nun and others that Alzheimer's disease takes decades to develop, and this disease has many important consequences in all aspects of a person's life.”
For Clarke and her colleagues, the sisters' willingness to open their lives, and ultimately their brains, to science remains the heart of the project.
“Their kindness and generosity made the Nun Study a significant and fundamental contribution to dementia research and continues to inspire us to continue our pursuit of understanding and treating this debilitating disease,” she said.
