The study, published in the June issue of the Journal of Clinical and Experimental Neuropsychology, provides important new evidence that either more years of formal education or better early brain development may help delay dementia in later life. The findings were drawn from the Nun Study, a longitudinal study of aging and Alzheimer's disease.
The study's first author James Mortimer, PhD, director of the USF Institute on Aging, reported that Catholic sisters who completed 16 or more years of formal education or whose head circumference was in the upper two-thirds were four times less likely to be demented than those with both smaller head circumferences and lower education. Head circumference has been shown in previous studies to be a good indicator of the volume or size of the brain.
"We did not find an association between education or head circumference and the presence of severe brain abnormalities characteristic of Alzheimer's disease pathology. This suggests that having higher education or a larger brain does not decrease the chances of Alzheimer's brain abnormalities, but rather allows the brain to function at a higher level despite the presence of these abnormalities," said Dr. Mortimer, a professor of epidemiology and biostatistics.
"Larger brain size and more education provide extra reserve that allows one to function normally in the presence of a brain disease like Alzheimer's, similar to the way a larger and better constructed dam is able to prevent a flood from occurring during a major storm.
"Head circumference is completely determined by age 12, at which time maximum brain size is attained. However, because education is a lifelong process, it is possible that elderly people can delay or even prevent the onset of dementia by keeping their brains active," Dr. Mortimer said. It is not yet known when in the life course formal education needs to occur for this protection to exist, he added.
The research team assessed 294 Catholic sisters for whom data on head circumference were available every year for 10 years. The nuns were tested for their cognitive abilities and completion of daily living tasks, and 111 were diagnosed with dementia. Sixty participants died and their autopsied brains were evaluated to assess the severity of brain abnormalities associated with AD.
The Nun Study, begun in 1992, has followed 678 Catholic sisters, initially 75 to 102 years of age, who are evaluated yearly and who have agreed to brain donation at the time of death. Supported by the National Institute on Aging, it is one of the first large autopsy studies to include normal as well as demented participants. The Nun Study is directed by Dr. David Snowdon of the University of Kentucky. Dr. Snowdon and Dr. William Markesbery, Director of the Sanders-Brown Center on Aging, are co-authors of the current study.
Journal of Clinical and Experimental Neuropsychology