The more you study, the later you drop - Education and terminal cognitive decline
Graciela Muniz-Terrera is a Senior Investigator Scientist at the MRC Lifelong Health and Ageing Unit at UCL
The terminal decline hypothesis suggests an acceleration of rate of cognitive decline before death, although information about the onset of faster decline is inconsistent and varies by ability examined. The identification of factors that may delay such onset is crucial for policy implementation, as such delay would imply that individuals spend a shorter period of time in the fast declining stages of life. Education is a modifiable risk factor usually considered as a proxy for cognitive reserve that has been shown to be associated with cognitive function and, in a few American studies, has also been shown to be associated with a later onset of preclinical dementia.
I was interested in testing whether education was also associated with later onset of faster decline before death, and whether this hypothesis was valid in a UK study.
With this aim, I used data from a deceased sample of participants on the Cambridge City over 75 Cohort Study, a population –representative longitudinal study of ageing that started in 1985 ( then known as the Hughes Hall Project for Later Life) recruiting individuals aged 75 and over for over 21 years living in the city of Cambridge, UK. These individuals were interviewed at study entry , and then at an average of 2, 7, 9, 11, 13, 17 and 21 years later by trained nurses who assessed their global cognition using the most widely used test of cognitive function, the Mini Mental State Exam.
The mean age at study entry was 81 years old and at death was 88 years old, and women accounted for 65% of the deceased sample. Study participants were asked about the age they left school, which was, on average 14.8 yrs.old.
We found that the onset of terminal decline happened, on average, at 6.2 years before death (SD = 0.2) and that, individuals who left school at an older age had a later onset of faster decline, although the onset was delayed by only 0.4 years for more educated individuals. Also, that rate of decline changed from 0.12 (SD = 0.021) points per year closer to death before the onset of faster decline to 0.91 (SD = 0.06) points per year closer to death after the onset of faster decline.
Our findings are encouraging for future public health interventions that could be implemented to shorten the most deteriorating stage of life.