A systematic evaluation of the psychological and behavioural effects of the combined consumption of glucose and caffeine and comparison to the effects produced by consuming either substance in isolation

Robertson, Bernadette and Sunram-Lea, Sandra (2019) A systematic evaluation of the psychological and behavioural effects of the combined consumption of glucose and caffeine and comparison to the effects produced by consuming either substance in isolation. PhD thesis, Lancaster University.

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Abstract

Extensive research has found glucose and caffeine to have beneficial effects on cognition and mood. Broadly, glucose has been found to improve memory and caffeine to improve attention and alertness. Relatively little research has investigated the effects of their combined consumption, although to date, similar effects on cognitive performance and mood have been found. The aim of this thesis was to systematically evaluate the behavioural effects of combined consumption of these substances and compare them with the effects of consuming either substance in isolation. Moderating factors, such as cognitive effort, were considered along with the evaluation of neural and neuroendocrine responses. The first study (chapter 2) found evidence of beneficial effects of caffeine, glucose and their combination on memory and mood, with individual effects varying across doses. However, concurrent measurement of the neuroendocrine response found no effects (chapter 3). Investigation into pre-retrieval administration of the substances memory performance (chapter 4) found no effects of any substance, in contrast to the beneficial effects found for pre-learning administration. A parallel assessment of glucose and caffeine on different attentional networks and systems (chapter 5) failed to find any effects on this aspect of cognitive performance. In chapter 6 the effects of the substances on participants who were in a sub-optimal state were examined. The findings were not able to show that effects of the substances can be more clearly elucidated when participants are not performing optimally. The final experimental study (chapter 7) investigated the effects of caffeine and glucose on neurocognitive processes, but no beneficial effects were found. Overall, the findings suggest that the effects of caffeine, glucose and their combination are modulated by dose and domain.