Impaired glucose tolerance at midlife predicts worse performance in a test measuring episodic memory after ten years, according to new research published in the journal Diabetes Care.
“Cognitive decline and memory disorders are major health problems in aging societies. Early prevention of memory disorders such as Alzheimer’s disease would be very useful,” said researcher Sini Toppala, a PhD student at the University of Turku in Finland.
“Previous studies have shown that diabetes is associated with decline in cognitive functions. Insulin resistance, a condition where the body is unable to respond sufficiently to the insulin secreted, is also linked to cognitive decline and Alzheimer’s disease. Measuring insulin resistance in clinical practice is challenging, but oral glucose tolerance test is a commonly used test which shows if the person being tested has diabetes or impaired glucose tolerance, both closely related to insulin resistance.”
The researchers examined data from 961 middle-aged individuals who participated in the Finnish population-based Health 2000 Examination Survey and a follow-up study conducted ten years later. Participants completed assessments of memory and other cognitive functions at baseline and during follow-up. They also completed two-hour oral glucose tolerance tests, which are used to screen for type 2 diabetes, gestational diabetes, and prediabetes.
A person is considered to have impaired glucose tolerance when the glucose level in a two-hour glucose tolerance test is elevated, but the diagnostic criteria for diabetes are not met.
The researchers found that heightened two-hour glucose tolerance at baseline was associated with subsequent declines in memory performance at the follow-up. In particular, heightened two-hour glucose tolerance predicted declines in performance of a word-list delayed recall test, a common test of episodic memory that is typically affected early in Alzheimer disease.
“Our study found that higher post-load blood glucose level (glucose measured following glucose drink) in a glucose tolerance test at midlife is associated with weaker performance in a memory test ten years later,” Toppala told PsyPost. “Glucose tolerance testing might be helpful in identifying patients with increased risk for future cognitive decline. Healthy lifestyle at midlife might be beneficial also regarding future cognitive performance.”
The researchers controlled for several known risk factors of memory disorders, such as age, education background, elevated blood pressure, elevated cholesterol level, obesity, type 2 diabetes, and smoking. But the study — like all research — includes some limitations.
“The exact mechanisms underlying the association between disturbances of glucose metabolism and cognitive function are not yet fully understood. Further research is needed,” Toppala said.
The study, “Oral Glucose Tolerance Test Predicts Episodic Memory Decline: A 10-Year Population-Based Follow-up Study“, was authored by Sini Toppala, Laura L. Ekblad, Matti Viitanen, Juha O. Rinne, and Antti Jula.