The study included 117 people who developed dementia out of an original cohort of 488 people. Researchers followed the participants for an average of six years using annual cognitive tests. Study participants ranged in formal education levels of less than three years of elementary school to people with postgraduate education.
The study found for each additional year of formal education, the rapid accelerated memory decline associated with oncoming dementia was delayed by about two-and-a-half months. However, once that accelerated decline stopped, the people with more education saw their rate of cognitive decline accelerate four percent faster for each additional year of education. Past research had shown that people with more education had more rapid memory loss after diagnosis of dementia.
"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," said study author Charles B. Hall, PhD, with Albert Einstein College of Medicine in Bronx, New York. "Our study showed that a person with 16 years of formal education would experience a rate of memory decline that is 50 percent faster than someone with just four years of education."
For example, a college graduate with 16 years of education whose dementia is diagnosed at age 85 would have started to experience accelerated memory decline nearly four years earlier at age 81. While a person with just four years of education who was also diagnosed at age 85 would have begun to experience a less rapid rate of decline around age 79, six years before diagnosis.
"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," said Hall. "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."
Hall says this is the first study to confirm important predictions of the effects of cognitive reserve in people with preclinical dementia. He also notes the study is limited since the participants were born between 1894 and 1908 and their life experiences and education may not represent that of people entering the study age range today.