To determine the impact of glycemic control, gender, and other relevant parameters on cognitive function during exposure to different blood glucose levels in patients with insulin-dependent diabetes mellitus (IDDM), we examined neuropsychologic function during experimentally induced periods of hyperglycemia and hypoglycemia.

We studied 20 men and 22 women, aged 18 to 44 years, with IDDM duration of 3 to 14 years and HbA1 values ranging from 5.8% to 18.0% (nondiabetic range 5.4% to 7.4%). We used a controlled experimental setting involving tests of sensory perceptual processing, simple motor abilities, attention, learning and memory, language, and spatial and constructional abilities at plasma glucose levels of 2.2, 5.6, 8.9, 14.4, and 21.1 mmol/L. Patients were blind to the glucose level. Tests used at each glucose level included reaction time (simple and choice), digit vigilance, trail making part B, word recall, digit sequence learning, and verbal fluency.

All aspects of neuropsychologic function were diminished at 2.2 mmol/L when compared with basal levels of performance at 8.9 mmol/L. whereas no alterations were observed at 14.4 or 21.1 mmol/L. Tests involving associative learning, attention, and mental flexibility were the most affected during hypoglycemia. Glycemic control was not correlated with neuropsychologic function at any glucose level. Women demonstrated less of an impairment in neuropsychologic function than men at 2.2 mmol/L.

Cognitive function in IDDM patients was generally well-preserved even at substantially elevated blood glucose levels. Deficits in ail relevant areas of cognitive function occurred during hypoglycemia (2.2 mmol/L). irrespective of prior glycemic control, and women with IDDM were less cognitively impaired than men with IDDM during hypoglycemia.