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Background Long-standing concern about the effects of type 1 diabetes on cognitive ability has increased with the use of therapies designed to bring glucose levels close to the nondiabetic range and the attendant increased risk of severe hypoglycemia.
Methods A total of 1144 patients with type 1 diabetes enrolled in the Diabetes Control and Complications Trial (DCCT) and its follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) study were examined on entry to the DCCT (at mean age 27 years) and a mean of 18 years later with the same comprehensive battery of cognitive tests. Glycated hemoglobin levels were measured and the frequency of severe hypoglycemic events leading to coma or seizures was recorded during the follow-up period. We assessed the effects of original DCCT treatment-group assignment, mean glycated hemoglobin values, and frequency of hypoglycemic events on measures of cognitive ability, with adjustment for age at baseline, sex, years of education, length of follow-up, visual acuity, self-reported sensory loss due to peripheral neuropathy, and (to control for the effects of practice) the number of cognitive tests taken in the interval since the start of the DCCT.
Results Forty percent of the cohort reported having had at least one hypoglycemic coma or seizure. Neither frequency of severe hypoglycemia nor previous treatment-group assignment was associated with decline in any cognitive domain. Higher glycated hemoglobin values were associated with moderate declines in motor speed (P=0.001) and psychomotor efficiency (P<0.001), but no other cognitive domain was affected.
Conclusions No evidence of substantial long-term declines in cognitive function was found in a large group of patients with type 1 diabetes who were carefully followed for an average of 18 years, despite relatively high rates of recurrent severe hypoglycemia. (ClinicalTrials.gov number, NCT00360893
[ClinicalTrials.gov]
.)
Source Information
The members of the writing committee — Alan M. Jacobson, M.D., and Gail Musen, Ph.D., Joslin Diabetes Center and Harvard Medical School, Boston; Christopher M. Ryan, Ph.D., and Nancy Silvers, R.N., University of Pittsburgh School of Medicine, Pittsburgh; Patricia Cleary, M.S., and Barbara Waberski, M.S., George Washington University, Rockville, MD; Amanda Burwood, B.S., and Katie Weinger, Ed.D., Joslin Diabetes Center, Boston; Meg Bayless, R.N., University of Iowa College of Medicine, Iowa City; William Dahms, M.D. (deceased), Case Western Reserve University, Cleveland; and Judith Harth, R.N., University of Western Ontario Schulich School of Medicine, London, ON, Canada — and the DCCT/EDIC Study Research Group assume responsibility for the overall content and integrity of the article.
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