Higher Education Delays Dementia Onset but Is Linked to More Rapid Progression

October 29, 2007 — Higher education delays the onset of accelerated cognitive decline, but once it begins, deterioration is more rapid in better-educated individuals, new research suggests. Investigators at the Albert Einstein College of Medicine, Bronx, New York, found that for each additional year of formal education, the rapid accelerated memory decline associated with oncoming dementia was delayed by about 2-1/2 months.
However, once that accelerated decline stopped, individuals with more education had their rate of cognitive decline accelerate 4% faster for each additional year of education.
"Higher levels of education delay the onset of dementia, but once it begins, the accelerated memory loss is more rapid in people with more education. Our study showed that a person with 16 years of formal education would experience a rate of memory decline that is 50% faster than someone with just 4 years of education," principal investigator Charles B. Hall, PhD, said in a statement from the American Academy of Neurology.
The study is published in the October 23 issue of Neurology.
Brain Maintains Function Despite Damage
According to Dr. Hall and colleagues, this is the first study to confirm the long-held hypothesis of "cognitive reserve," which postulates that individuals with more education begin to experience acceleration in cognitive decline closer to the time of diagnosis than those with lower reserve but that their rate of decline is more rapid after the time of acceleration due to increased disease burden.
"This rapid decline may be explained by how people with more education have a greater cognitive reserve, or the brain's ability to maintain function in spite of damage. So while they're often diagnosed with dementia at a later date, once the cognitive reserve is no longer able to compensate for the damage that's occurred, then the symptoms emerge," he said.
To determine the influence of education on rates of memory decline, researchers studied 117 subjects who developed incident dementia during their participation in the Bronx Aging Study, which included 488 healthy, community-dwelling individuals aged 75 to 85 years without baseline dementia enrolled between 1980 and 1983.
Study subjects had detailed cognitive assessments, including the Busche Selective Reminding Test (SRT), which has shown to be a predictor of prevalent and incident dementia, and annual follow-up visits.
Using a change-point model, the investigators estimated the time at which the rate of decline began to accelerate. In addition, using longitudinal study data, they calculated the preacceleration and postacceleration rates of decline.
Such models, the authors explain, consider the date of diagnosis as time zero and look backward in time at cognitive trajectories that precede diagnosis.
"If the cognitive-reserve hypothesis is correct, memory decline will accelerate closer to the time of dementia diagnosis and that decline will be more rapid in persons with more education," they write.
Possible Masking Effect
The median follow-up time before dementia diagnosis was 5.6 years. A total of 61 (52%) of study participants received a clinical diagnosis of probable or possible Alzheimer's disease (AD), 24 (21%) were diagnosed with vascular dementia (VaD), 24 (21%) had a combination of both AD and VaD, and 8 (7%) were diagnosed with other subtypes.
According to the article, of the total study population, 9 participants had 3 or fewer years of formal education, 23 had 4 to 6 years, 37 had 7 to 9 years, and 27 had 10 to 11 years. Of 21 individuals who had completed high school, 2 had some college education, 4 had college degrees, and 7 had both college degrees and at least some postgraduate education.
The investigators found that each additional year of formal education delayed the time of accelerated decline on the SRT by 0.21 years. Postacceleration, the rate of memory decline was increased by 0.10 points per year for each additional year of formal education.
According to the authors, the findings' generalizability may be limited by the fact that the participants were mainly middle class and white. Furthermore, because study subjects were born between 1894 and 1908, their life experiences may not be representative of today's population.
"Nevertheless," they write, "this is the first study to confirm important predictions of the cognitive-reserve hypothesis in persons with preclinical AD. A potential implication is that early signs of dementia may be masked in persons with higher educational achievement."
They add that their future research will examine other measures of cognitive reserve, including IQ and occupational achievement, as well as factors that may preserve cognitive reserve, such as participation in leisure activities.
The study was supported by the National Institute of Aging. The study authors have disclosed no relevant financial relationships.
Neurology. 2007;69:1657-1664.