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 Institute on Aging project that began in 1990 with 678 School Sisters of Notre Dame, produced findings that continue to guide dementia research today, even though every sister who took part has now died.
Their contribution matters now because researchers are still publishing on the data they left behind. In 2025, Alzheimer’s & Dementia, The Journal of the Alzheimer’s Association published a scientific review summarizing decades of findings, calling the project “an iconic longitudinal study of aging and dementia.” With more than 600 brain autopsies completed and a rare archive of early-life records, the study’s influence stretches well beyond the convent walls where it began.
How the Nun Study Began and Why Researchers Chose Catholic Sisters
David Snowdon, Ph.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. He expanded that work into the full Nun Study in 1990, enrolling 678 sisters from SSND communities across the United States. Most participants were between 75 and 102 years old at enrollment. Of the 1,027 eligible sisters, 678, about 66 percent, agreed to take part and committed to annual assessments of memory, language, reasoning, physical health and daily functioning.
The sisters were an unusually valuable research population 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 shared comparable housing, nutrition, health care, income and social networks, variables that normally muddy epidemiological research.
“Normally, it’s hard to pinpoint what causes some people to develop dementia while others remain healthy because people can have very different lifestyles, environments and biology, some smoke, some don’t, some have better access to health care than others, some may be more genetically disposed to disease,” Kyra Clarke, a doctorate student at UT Health San Antonio and one of the review’s authors, said, per EWTN News.
“But Catholic sisters from the same order share the same environment for most of their adult lives, with similar marital histories and daily routines,” she said. “It is difficult to find a community of people with such consistent and comparable lifestyles. This makes it easier to figure out what factors truly increase or decrease the risk of dementia.”
What the Brain Donations Revealed About Alzheimer’s and Dementia
Brain donation was a prerequisite for joining the study. By the end, 98 percent of participants had undergone a brain autopsy, and more than 600 autopsies were completed, one of the largest collections of brain tissue ever assembled for Alzheimer’s research. Neuropathologists conducting the exams were blinded to participants’ cognitive test results, allowing direct comparison between brain changes and thinking and memory abilities recorded during life.
Researchers also drew on medical records, educational transcripts, autobiographies the sisters had written in early adulthood and genetic information from blood or tissue samples. The findings reshaped the field in two ways. Some sisters carried 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 through those autobiographies and school records, was associated with better cognitive outcomes decades later.
Together, those results helped establish the concept of cognitive reserve, the idea that lifelong intellectual engagement may help some people maintain memory and thinking even when their brains show substantial disease. The work also demonstrated that multiple brain diseases frequently coexist in older adults and that those overlapping pathologies raise the likelihood of dementia.
What the Nun Study Found About Nutrition, Folate and Brain Health
The research team also examined how diet and nutrient levels connected to brain aging. Sisters with lower blood folate, known as vitamin B9, tended to show greater brain shrinkage and poorer cognitive performance than those with higher levels. Lower folate concentrations, especially alongside elevated homocysteine, were associated with a higher likelihood of Alzheimer’s disease and cognitive impairment.
The findings did not prove that folic acid prevents dementia. But they suggested that maintaining adequate folate status may be one component of healthy brain aging, a piece of a larger picture that includes education, cognitive stimulation and coexisting health conditions.
“The Nun Study really emphasized that maintaining cognitive health is a lifelong task and emphasized the importance of education and cognitive stimulation in reducing the risk of dementia,” Clarke said.
Why the Nun Study Still Shapes Dementia Research Today
Although no living sisters remain in the study for cognitive assessments, neuropathology work continues. The School Sisters of Notre Dame note on their website that “the sisters involved continue to impact Alzheimer’s research through the gift of their brain donations.” Margaret Flanagan, who directs the ongoing research at UT Health, has personal ties to the congregation, as several family members attended Chicago’s Academy of Our Lady, an SSND-operated school. Researchers still meet regularly with SSND representatives to share updates.
The influence on the wider scientific community has been significant from the start. “The Nun Study has certainly been pioneering,” said Dr. Richard Suzman, chief of demography and population epidemiology at the National Institute on Aging, per The New York Times. “It’s helped change the paradigm about how people think about aging and Alzheimer’s disease.”
Dr. Robert P. Friedland, professor of neurology at Case Western Reserve University, pointed to what made the design so unusual. “I think the Nun Study is very important because it uses information obtained about people before the period of illness,” he said. “So we know from the Nun Study and others that Alzheimer’s disease takes several decades to develop, and the disease has many important effects on 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 an iconic and groundbreaking contribution to dementia research and continuously inspires us to keep pushing towards understanding and treating this debilitating disease,” she said.
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