Limits on learning: The effect of hypoglycemia and hyperglycemia on cognitive function in adults with IDDM

Glucose is the main fuel for the brain. Alterations in the blood glucose levels can affect cerebral functioning and, in turn, cognitive functioning. More than one million Americans who suffer from insulin-dependent diabetes mellitus (IDDM) are at risk for disruptions in cognitive functioning because both high and low blood glucose levels are associated with IDDM and its treatment. This study investigated the relationship between blood glucose level and cognitive functioning and identifies adults with IDDM who may experience cognitive impairment in short-term memory, sustained attention, and selected attention during glucose fluctuation.; The sample of 42 adults with IDDM from a Joslin Diabetes Center study underwent procedures that experimentally induced hyperglycemia (high blood glucose) and hypoglycemia (low blood glucose). Subjects completed different versions of a battery of neuropsychological tests at baseline, hypoglycemia and hyperglycemia. My study used an innovative analytical approach: using growth modeling techniques to represent individual change in cognitive function over controlled changes in blood glucose level rather than over time. Specifically, I investigated (1) the average pattern of cognitive functioning change during blood glucose fluctuation, (2) whether the blood glucose/cognitive functioning relationship differed across adult subjects with IDDM, and, (3) whether inter-individual differences could be predicted by easily identifiable characteristics such as disease duration, education, level of diabetes control, and gender.; Hypoglycemia interfered with all three cognitive functions, suggesting that IDDM patients should test glucose levels before important learning or evaluation tasks. Men experienced more deterioration in selected and sustained attention than women. Educated individuals did better on challenging tasks but fared worse on a tedious task than those with less education. Longer disease duration was associated with better short-term memory for numbers. In addition, familiarity with a task offered a measure of protection during glucose fluctuations. Thus, extended practice with important skills such as using glucose monitoring equipment may help IDDM patients to treat hypoglycemia early and safely. Academic and health educators as well as IDDM patients should incorporate this information when planning educational programs.