Cognitive functioning is susceptible to the level of blood glucose

Rationale: It is traditionally assumed that under normal conditions the brain is well supplied with glucose, its basic fuel. However, given the limited stores of glucose in the brain and its dependence on a continual peripheral supply of glucose, it was considered whether the availability of glucose, and the ability to efficiently utilise glucose, affects cognitive functioning. Objective: There is increasing evidence that the provision of blood glucose influences memory. To date, the impact of blood glucose on non-memory task performance has received little attention. The present study investigated whether the performance of non-memory tasks was susceptible to the level of blood glucose. Two studies are reported in which the influence of a glucose containing drink on six cognitive tests was considered. Results: The consumption of a glucose containing drink resulted in faster performance on the Porteus Maze and greater Verbal Fluency. Higher levels of blood glucose on arrival at the laboratory were associated with better performance on the Water Jars test. With both the Porteus Maze and Block Design tests, after taking a glucose drink, poor performance was associated with blood glucose that remained at higher levels. Conclusion: It was suggested that we should consider two physiological mechanisms, firstly, that an equilibrium develops between plasma and brain glucose, such that those with higher levels of blood glucose could be expected to have higher levels of brain glucose and secondly, whether there are individual differences in the efficiency with which glucose is taken from the blood; those with poor glucose control perform some cognitive tasks more poorly.