Effects of caffeine and glucose, alone and combined, on cognitive performance.

Objective: To study the effects of consuming caffeine and glucose, alone and combined, on cognitive performance.

Methods: Seventy-two healthy subjects (36 women; age range 18-25) were tested early in the morning, having fasted overnight. Using a double-blind, randomised design, subjects received one of the following beverages: water (150 ml); water plus 75 mg of caffeine; water plus 75 g of glucose; water plus and 75 mg of caffeine and 75 g of glucose. Attention, manual dexterity, visuo-spatial and frontal functions, memory (immediate, consolidation and working) and subjective state were all assessed.

Results: The combination of caffeine and glucose had beneficial effects on attention (sequential reaction time tasks) and on learning and consolidation of verbal memory, effects not being observed when either substance was administered alone. Caffeine only showed improvement in simple reaction time and glucose in simple and one sequential reaction time tasks and in the manual dexterity assembly task.

Conclusions: The results indicate that the synergistic effects of caffeine and glucose can benefit sustained attention and verbal memory, even with adequate levels of activation of the subjects. However, further studies are required, controlling for different levels of cognitive effort and also considering measurements of neural activity.