The University of Alberta study, published in the journal Neuropsychology, also found that mental deterioration was no less in younger diabetics than in an older group, suggesting the damage is done early in the disease and remains stable thereafter.

"The good news is that, at this point, the cognitive slowing would not be notable in most older diabetes patients' everyday life activities," said Roger Dixon, a cognition and aging researcher and the report's co-author.

"It may be noticed, however, if the patient is involved in technical psychomotor tasks (such as video games) requiring quick and accurate responses or monitoring," he said in a Times of London report.

"The bad news is that this slowing may indicate the 'leading edge' of progressive cognitive decline occurring with diabetes, and it will likely get worse without careful disease management," he said.

Dixon urged people with serious cases of type 2 diabetes to be screened for cognitive changes to make sure they get the right medication and advice on diet or mental training.

Type 2 diabetes is a chronic, lifelong disease marked by high blood sugar. It begins when the body does not respond correctly to insulin, a hormone released by the pancreas.

Ninety percent of the estimated 23.6 million people in the United States diagnosed with diabetes have type 2.