The effect of IQ level on the degree of cognitive deterioration experienced during acute hypoglycemia in normal humans

Acute hypoglycemia provokes a deterioration in cognitive function both in normal individuals and patients with Type 1 diabetes. A large interindividual variation is observed in the magnitude of the cognitive dysfunction observed during hypoglycemia, the reasons for which are not apparent. This study examines whether IQ level exerts a differential effect on the impairment of cognitive performance induced during acute hypoglycemia. Twenty-four nondiabetic participants were divided into high and average IQ groups according to their results on the Alice Heim 4 test and the National Adult Reading Test. Cognitive function was assessed during hypoglycemia using the following cognitive test battery: Paced Auditory Serial Addition Test (PASAT), Rapid Visual Information Processing (RVIP), Trail-Making B (TMB), Digit Symbol Substitution Test (DSST), and Four-Choice Reaction Time (CRT). In Condition A (the placebo condition), the participants' blood glucose was maintained at 4.5 mmol/1 throughout. On two occasions (Conditions B and C), the blood glucose was stabilized at 4.5 mmol/1 for 30 min, lowered to 2.5 mmol/1 (hypoglycemia) for 60 min, and restored to 4.5 mmol/1 for 30 min. Under each condition, the cognitive test battery was performed immediately after stabilization of blood glucose at 4.5 mmol/1, and the battery was repeated as follows: Condition A—after a further 40 min of euglycemia; Condition B—after 5 min of hypoglycemia; Condition C—after 40 min of hypoglycemia. Multivariate analysis of variance demonstrated a detoriation in cognitive performance as a result of hypoglycemia irrespective of IQ group ( p< .005). Acute hypoglycemia induced a significant deterioration in cognitive function in all tests except TMB ( p< .05). No overall effect of IQ on deterioration in cognitive performance could be ascertained, although univariate analysis of variance revealed an IQ effect on two of the test: The avergae IQ group deteriorated significantly less than the higher IQ group during hypoglycemia in the 4-s PASAT task ( p = .03) and tended to have higher false alarm rates in the RVIP ( p = .06). In conclusion, individuals with a higher IQ do not appear to be protected from tge adverse effects of acute hypoglycemia on cognitive function.