Type 2 diabetes linked to cognitive decline

By establishing a link between cognitive decline and type 2 diabetes in the January 2009 issue of Neuropsychology, researchers at the University of Alberta provided another reason to be concerned about the rising incidence of this disease in adults around the world.

Conducted as part of the Victoria Longitudinal Study that follows three independent samples of initially healthy adults between the ages of 53–90 at three-year intervals, the team of researchers led by Dr Roger Dixon compared cross-sectional data of 41 adults diagnosed with adult-onset Type 2 diabetes to 424 healthy adults.

“Neurocognitive speed tests showed that older diabetes patients are reliably slower than older adult control participants,” explained Dixon, a Canada Research Chair and U of A professor of psychology, via email correspondence with the Gateway.

“Cognitive slowing may be an especially sensitive marker of the effects of diabetes on brain function.”
Diabetes, with its worldwide prevalence doubling from 1995 to 2005, has become a major concern to the medical field, resulting in the Centers for Disease Control and Prevention (CDC) marking the rise as an epidemic. Out of the 12 per cent of Canadians over the age of 60 that are diagnosed with diabetes, an estimated 90 per cent of these incidences are classified as type 2.

Though the exact origin of type 2 diabetes has not been identified, Dixon pointed to some factors that increase the likelihood of developing the disorder.

“Among the key risk factors are increasing age, obesity, and lack of physical activity,” he explained.
Using cognitive neuropsychological tests that measured performance in five domains, Dixon discovered that healthy adults performed significantly better in two domains: executive functioning and neurocognitive speed.

The former involves the ability to monitor and control ongoing cognitive operations, including abstract thinking, planning, and regulation of appropriate and inappropriate behaviour. The latter is a measure of processing speed, a domain that is sensitive to normal aging and early cognitive impairment.

On the other hand, tests of episodic and semantic memory, verbal fluency, reaction time, and perceptual speed did not yield significant differences. These findings suggest that diabetic patients will be able to carry out everyday actions without any noticeable deficits, as long as they are not performing tasks that require higher levels of monitoring and response.

In addition, the researchers noted that the performance gap between the healthy adults and diabetic group did not widen in the older group of participants. This suggests that these declines in cognitive function are early onset symptoms of the disease.

While the results are significant, Dixon notes that there are many questions that still need to be addressed about the effects of diabetes on cognitive function. Though they were able to establish a link between decline in cognitive abilities and the disorder, the reason behind this deficit has yet to be determined.

“At the basic biological level, the specific pathogenic processes that lead to type 2 diabetes require much further research, although several risk factors have been identified. In general, it would appear that vascular health in the brain is part of the network of causes of cognitive decline,” Dixon described.

“This is supported by the findings that vascular diseases are associated with diabetes. They also can have effects on cognition in normal aging and neurodegenerative diseases.”

In the meantime, Dixon explained that certain strategies can be adopted to minimize the effects of type 2 diabetes and improve the cognitive skills that are impacted.

“Older diabetes patients should meticulously follow the recommendations of their personal physician. Careful management of the disease and continued practice of these cognitive skills can help maintain cognitive performance in everyday life,” Dixon advised.

“Physical activity and exercise is often recommended for the disease, and this can have beneficial effects on basic neurocognitive skills.”