Type 2 diabetes may slow mental processing speed

NEW YORK (Reuters Health) - New research shows that among the mental abilities that are affected by type 2 diabetes, the speed at which the brain processes information appears to be the most severely impaired, particularly in patients with undiagnosed disease.

Findings from several studies have linked type 2 diabetes with cognitive dysfunction. However, it was unclear which cognitive processes were most affected and how undiagnosed diabetes and abnormal blood glucose (sugar) levels influenced cognitive performance.

To investigate, researchers analyzed data from 1,917 elderly men and women enrolled in the AGES Reykjavik Study - a large population-based study that ran from 2002 to 2006. The AGES study explored genetic and other risk factors for a variety of age-related conditions including cognitive impairment.

The study subjects, who did not have dementia, included 955 nondiabetic individuals, 744 with impaired fasting glucose (a precursor to full blown diabetes), 163 with diagnosed diabetes, and 55 with undiagnosed diabetes.

A battery of brain function tests revealed that patients with diagnosed diabetes had significantly slower mental processing speed, compared to nondiabetic subjects, Dr. Jane S. Saczynski, from the University of Massachusetts Medical School, Worcester, and colleagues report in the American Journal of Epidemiology.

Memory performance and "executive function" -- the ability to plan, schedule, and multi-task -- were comparable in the two groups, except for those who had diabetes for 15 years or longer, for whom significantly poorer executive function was also observed.

For those with undiagnosed diabetes, both processing speed and memory performance were significantly worse relative to their non-diabetic peers.

For patients with impaired fasting glucose (pre-diabetes), cognitive performance in all three areas was on par with that seen in nondiabetic subjects.

"Given the increasing prevalence of type 2 diabetes in older adults and the complexity of disease management in these high-risk individuals, future treatment protocols should be developed with the cognitive status of patients with type 2 diabetes in mind," the research team concludes.

SOURCE: American Journal of Epidemiology, November 15, 2008.