Caffeine, chocolate, performance, and mood

Background: There has been considerable research on the effects of caffeine on performance and mood. This means that it can now be used as a positive control to benchmark the effects of less studied foods and drinks. Chocolate has been less frequently investigated, and the present study examined the effects of caffeine given in coffee and dairy milk chocolate in the same experiment. Methods: A parallel groups design was used to investigate the effects of 60 mg caffeine given in coffee and dairy milk chocolate. Forty-eight participants completed the study, which involved a practice session and two test sessions before and after the caffeine/chocolate manipulations. The test battery involved mood rating and performance tasks measuring a variety of functions (motor, episodic memory, working memory and attention). Participants either carried out the sessions in the morning (10.30 start) or afternoon (15.30 start). Impulsivity scores were recorded before the start of the study. Results: Caffeine was associated with feeling more clumsy but more efficient. The effect of chocolate on mood varied with the time of testing. Those given chocolate in the afternoon felt more friendly, quick-witted and excited than the no chocolate group. This pattern of results was reversed for the morning groups. Chocolate had no effects on the performance tasks. Selective effects of caffeine were observed, with no effect on the motor or episodic memory tasks but the faster performance of the logical reasoning task after caffeine. Interactions between caffeine and impulsivity were found in the search and memory speed and Bakan accuracy analyses. High impulsive participants showed worse performance than low impulsive people in the decaffeinated conditions, and the opposite was found after caffeine. Conclusion: These results demonstrate that, compared to caffeine in coffee, dairy milk chocolate produces few behavioural changes. The effects of caffeine were dependent on the type of task and personality, which confirms earlier research using similar methodology