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As it has been suggested that blood glucose might play a role in the action of some cognitive enhancing drugs, the influence of glucose containing drinks on human memory was examined. In a double-blind study the influence was examined of a drink containing 50 g glucose, or a placebo, on the ability to recall a word list. There was a significant correlation between blood glucose values and the number of words recalled. Those whose blood glucose levels were increasing remembered significantly more words than those whose blood glucose levels were falling. No relationship was found between blood glucose and performance on a test of spatial memory. In a second study blood glucose levels were raised for 2 h by taking a series of glucose-containing drinks. The number of words recalled from a word list correlated significantly with blood glucose levels but not with recall of a Wechsler story. The glucose-induced improvement in memory did not occur only in those whose blood glucose levels were initially low; rather it occurred irrespective of initial blood glucose level.

This study was undertaken to determine whether the internal clock contributes to the hormone and metabolic responses following food, in an experiment designed to dissociate internal clock effects from other factors.

Although previous studies have demonstrated enhanced mood and memory in humans following the consumption of glucose drinks, the effect of increasing blood glucose levels on other tasks has not received the same attention. In the present study, inspection time was unaffected by glucose drinks and blood glucose levels. However, increasing blood glucose levels resulted in faster decision times when reaction time was measured. It is concluded that speed of processing is faster when the availability of glucose to the brain is increased. The possibility that the glucose-induced improvements in reaction time reflect an increased synthesis of acetylcholine is discussed.

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