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The aim of the present study was to examine the effects of breakfast and caffeine on performance, mood and cardiovascular functioning in the late morning and after lunch. Forty-eight subjects were tested at 07.45 and subjects then assigned to one of the four conditions formed by combining caffeine and breakfast conditions. Subjects in the caffeine condition were given a dose of 4 mg/kg, the caffeine manipulation being double blind. At 11.15 subjects were given another coffee (subjects remained in the same caffeine condition) and had lunch at 12.30. Performance was examined prior to lunch (11.30) and after lunch (14.00). Effects of breakfast on recognition memory (lower false alarm rate) and logical reasoning (reduced accuracy) were found in the late morning but not after lunch. However, a semantic processing task was performed more slowly by the breakfast group after lunch. Caffeine improved performance on a sustained attention task, the logical reasoning task and semantic memory task. Subjects given caffeine also reported greater alertness and feelings of well-being, whereas the effects of breakfast on mood changed from the late morning to early afternoon. Few interactions between breakfast and caffeine conditions were obtained.

An experiment was carried out to examine the effects of coffee on performance and alertness in the day and at night. The results showed that caffeinated coffee had a beneficial effect on alertness and improved performance on a variety of tasks in both day and night sessions. The effects were often very large. For example, at night, consumption of caffeinated coffee produced comparable alertness ratings to the day-time ratings given when juice was drunk. In contrast to the effects of caffeinated coffee, the difference between the decaffeinated coffee and juice were small and variable. Overall, these results clearly demonstrate the beneficial effects of consuming caffeinated coffee, and show that this effect is comparable in the day and night.

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