ADA: Cognitive Function Preserved with Tight Glucose Control

WASHINGTON, June 12 - Concerns that hypoglycemia from tight glucose control could lead to impaired cognitive function can be laid to rest, researchers reported here.

In a long-term follow-up of more than 1,000 patients with type 1 diabetes who were part of the cohort of the landmark Diabetes Control and Complications Trial (DCCT), investigators found no changes over time in any of eight cognitive domains that had been monitored.

"Now we know that patients don't have to worry about damaging their mental abilities as they work to significantly decrease their risks of developing diabetic retinopathy, neuropathy, nephropathy, and cardiovascular disease," reported Alan M. Jacobson, M.D., of the Joslin Diabetes Center in Boston at the American Diabetes Association meeting.

The DCCT, which ended in 1993, followed patients with type 1 diabetes for a decade, ending in 1993. The trial conclusively demonstrated the benefits of tight glucose control for preventing diabetes-associated complications.

In that trial, patients who managed to maintain glucose at a near-normal physiologic level had a threefold risk for severe hypoglycemia, leading to fears that frequent episodes of hypoglycemia and its attendant consequences (confusion, irrational behavior, convulsions, and loss of consciousness) could have a deleterious effect on cognitive function as patients aged.

In the current study, which is part of the DCCT follow-up called Epidemiology of Diabetes Interventions and Complications Study (EDIC), investigators looked at data on 1,059 of the participants in the DCCT, or about 75% of the original cohort.

Of these patients, 537 received intensive insulin therapy with either an insulin pump or three or more daily insulin injections, while 522 continued with what was at the time conventional therapy of one or two insulin shots per day.

During the DCCT the patients were evaluated with a battery of neuropsychological tests looking at cognitive abilities in eight domains, including problem solving, learning, short-term memory, delayed recall, spatial information, attention, psychomotor efficiency and psychomotor speed.

The authors used a stricter definition of hypoglycemic event, limiting it to episodes of diabetic coma or seizure, In the original trial the definition included any event that required the assistance of another person.

During the 6.5 year follow-up period of the current study, 652 patients reported no hypoglycemic events resulting in coma or seizure, 348 reported having one to five events, and 59 patients reported having more than five events.

When the patients were followed with the same neuropsychological tests for the current study, the researchers saw no change in regard to hypoglycemia over baseline in any of the eight domains after adjusting for age, gender, years of education, length of followup and number of cognitive tests taken. The findings were true for patients in both the intensive and conventional glucose control groups.

When they looked at HbA1c levels, however, they found that higher levels (indicating less-tight glucose control) were associated with modest declines in motor speed and psychomotor efficiency in the conventional treatment group, but not significant changes in any of the other domains, and that there was a significant difference in this measure favoring the intensive glucose control group.

The overall findings should be reassuring to patients who are zealous about controlling their blood glucose levels, Dr. Jacobson said.

"While acute episodes of hypoglycemia can impair thinking and can even be life-threatening, patients with type 1 diabetes do not have to worry that such episodes will impair their long-term abilities to perceive, reason, and remember," he said.