Written by: Catharine Paddock
Medical News Today
24 Oct 2007
A new US study suggests that people with more years of formal education experience the onset of memory decline associated with dementia later, but once it starts it declines more rapidly, compared to people with fewer years of education.
The study is published in the 23rd October issue journal Neurology and is the work of Dr Charles B Hall, from the Albert Einstein College of Medicine in Bronx, New York and colleagues.
Hall said that:
"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."
He and his colleagues found that a person with 16 years of formal education experienced a 50 per cent faster rate of memory decline than someone with only 4 years of education.
The researchers wanted to test something called the cognitive reserve hypothesis. This suggests that people with more years of education have a reserve of cognitive ability that hides (and this can be without the person realising it) the onset of memory decline (for instance they use thinking skills to work out answers to memory tests). This could explain why low education is a well known risk factor for Alzheimer's Disease (AD), a condition that is characterised by accelerated memory decline.
Hall and colleagues followed 488 people in the Bronx Aging Study of whom 117 developed dementia. The participants underwent detailed assessment of their cognitive skills at the start of the study, and also every year during the 6 years of follow up, when they completed a memory test called the Buschke Selective Reminding Test. Their formal education ranged from fewer than 3 years of elementary school to completion of postgraduate education.
The researchers estimated the point at which the rate of cognitive decline began to accelerate (the change point as they called it), and the rates of decline before and after this point.
They found that every additional year of formal education delayed the change point by 0.21 years (2.5 months). After the change point, the rate of memory decline increased by 0.10 points for each year of additional formal education. This translated to a 4 per cent faster rate of decline for each additional year of formal education.
The researchers gave an example. The onset of accelerated memory decline for a college graduate with 16 years of formal education who is diagnosed with dementia at 85 years of age would have started four years earlier, at age 81. But a person with only 4 years of formal education, who is diagnosed at the same age of 85, would have started to experience a slower rate of decline six years before diagnosis, at age 79.
This seemed to reflect previous research findings that showed people with more years of education suffered memory loss more quickly once they were diagnosed with dementia, wrote the researchers.
The researchers concluded that:
"As predicted by the cognitive reserve hypothesis, higher education delays the onset of accelerated cognitive decline; once it begins it is more rapid in persons with more education."
Commenting on the findings, Hall said that:
"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 added.
The researchers wrote that while their study was important because it was the first to test the cognitive reserve hypothesis in people with preclinical dementia, they pointed out that the people in the study were born at the turn of the 20th century and their life experiences and education may not be representative of people currently in education today.
"Education delays accelerated decline on a memory test in persons who develop dementia."
Hall, C. B., Derby, C., LeValley, A., Katz, M. J., Verghese, J., Lipton, R. B.
Neurology 2007 69: 1657-1664