Type 2 diabetes is a chronic condition that affects the body's insulin production and blood sugar levels. New research, however, suggests that the scope of this condition may be broader than previously thought, as scientists find a link between type 2 diabetes and cognitive decline over 5 years.

Michele Callisaya, from the University of Tasmania in Hobart, Australia, led the new research. Callisaya and her colleagues set out to investigate if there was an association between type 2 diabetes, on the one hand, and brain atrophy and cognitive decline, on the other.

Moreover, in case the researchers found such a connection, they wanted to discover whether there was a causal relationship underlying it.

The researchers recruited 705 people aged between 55 and 90 years from the so-called Cognition and Diabetes in Older Tasmanians study and took measures of the participants' brains and cognition.

To the authors' knowledge, this is the first study to compare both cognition and brain size among people with and without type 2 diabetes. The results appear in Diabetologia, the journal of the European Association for the Study of Diabetes.

Type 2 diabetes tied with cognitive decline

Of the total number of participants, 348 had type 2 diabetes, and 357 did not have the condition. Callisaya and colleagues used MRI scans to examine the ventricular and total brain volume, which are both markers of brain atrophy.

The researchers also measured global cognitive function and cognitive function across seven domains at three different time points over 4.6 years.

Callisaya and colleagues adjusted the results for "age, sex, education, and vascular risk factors," including smoking, cardiovascular events, such as heart attack, stroke, or hypertension, as well as high cholesterol and body mass index (BMI).

The analysis revealed strong associations between type 2 diabetes and cognitive decline—that is, a decline in verbal memory and verbal fluency.

The researchers also applied a "test of mediation" to see if "brain atrophy explained associations between type 2 diabetes and cognitive decline." However, they found no evidence that the rate at which the brain atrophied had any impact on the association between diabetes and cognitive function.

Furthermore, the analysis found no difference in the rate at which the brain shrunk between people with and people without diabetes, even though people with diabetes did have greater brain atrophy at the start of the study.

Why cognitive decline may lead to dementia

Finally, whereas people without diabetes showed a slight increase in verbal fluency over the course of the study, those with diabetes showed a decline.

"Such accelerated cognitive decline," write the authors, "may contribute to executive difficulties in everyday activities and health behaviors—such as medication compliance."

Such poor adherence to treatments, for instance, may in turn "poorly influence future vascular health and cognitive decline, and possibly an earlier onset of dementia in those with type 2 diabetes," suggest the authors.

Currently, 1 in 3 seniors in the US "dies with Alzheimer's or another dementia," according to the Alzheimer's Association, and almost 6 million people are currently living with the condition.

Callisaya and her colleagues conclude:

"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."

"If this is the case," they continue, "both pharmacological and lifestyle interventions to prevent brain atrophy in people with T2D may need to commence before older age."