A new Australian study published in the journal Diabetologia shows that type 2 diabetes (T2D) is linked to a decline in verbal memory and fluency over 5 years in older adults living in the community.
Previous studies have shown that T2D can double the risk of dementia in older people. Yet contrary to earlier research, the new study found that the decrease in brain volume often seen in older people with T2D was not directly linked to cognitive decline during this time period.
Instead, compared with people without T2D, those with T2D had evidence of greater brain atrophy at the beginning of the study.
In the new study, Dr Michele Callisaya and colleagues aimed to investigate whether type 2 diabetes is associated with greater brain atrophy and cognitive decline, and whether the two are linked. It is the first research to compare decline in both cognition and brain atrophy between people with and without T2D together in the same study.
The researchers recruited 705 people, ages 55 to 90, from the Cognition and Diabetes in Older Tasmanians (CDOT) study. There were 348 people with T2D (mean age 68 years) and 357 without (mean age 72 years) who underwent brain MRI (lateral ventricular and total brain volume — measures of brain atrophy) and neuropsychological measures (global function and seven cognitive domains) at three time points over a mean follow-up period of 4.6 years.
The results were adjusted for age, sex, education and vascular risk factors including past or current smoking, heart attack, stroke, high blood pressure, high cholesterol, and body mass index.
The findings reveal significant associations between T2D and greater decline in both verbal memory and verbal fluency.
Although diabetes patients had evidence of greater brain atrophy at the beginning of the study, there was no difference in the rate of brain atrophy between those with and without diabetes over the time course in this study. There was also no evidence that the rate of brain atrophy directly affected the diabetes-cognition relationship.
In people without type 2 diabetes, verbal fluency slightly increased on average each year, whereas it declined in those with type 2 diabetes.
“Such accelerated cognitive decline may contribute to executive difficulties in everyday activities and health behaviors — such as medication compliance — which in turn may poorly influence future vascular health and cognitive decline, and possibly an earlier onset of dementia in those with type 2 diabetes,” write the authors.
“In older community-dwelling people, type 2 diabetes is associated with a decline in verbal memory and fluency over approximately 5 years, but the effect of diabetes on brain atrophy may begin earlier, for example in midlife, given the evidence of greater brain atrophy in people with T2D at the start of the study.”
“If this is the case, both pharmacological and lifestyle interventions to prevent brain atrophy in people with T2D may need to commence before older age,” they say.