Caffeine, habitual caffeine consumption, alertness and cognitive performance.

Background: There has been extensive research on the effects of caffeine on behaviour. People differ in the amount of caffeine they regularly consume, and there has been research comparing the effects of caffeine on low and high consumers. This issue was examined here, and the effects of caffeine withdrawal and caffeine (100mg) on alertness and cognitive performance were investigated. Methods: Two groups of caffeine consumers were recruited. The high consumers had an intake of more than 200mg caffeine daily, whereas the low consumers ingested less than 20 mg caffeine daily. A double-blind cross-over design was used with all participants carrying out caffeine and placebo conditions. Each session had the following features. After overnight abstinence, participants carried out a baseline session at 09.00 to examine the possible effects of caffeine withdrawal. During the session, they rated their alertness and performed cognitive vigilance and five-choice serial response tasks. After the baseline session, the participants were given either caffeinated or decaffeinated coffee. A post-drink testing session was carried out one hour later. Results: There were no significant differences between the low and high consumer groups at baseline. Both groups of participants reported significantly greater alertness after caffeine at the start and end of the test session. Caffeine was also associated with significantly more hits in the cognitive vigilance task and more responses in the five-choice serial response task. There were no differences between the two consumer groups in the effects of caffeine. Conclusion: These results demonstrate that caffeine increases alertness and improves sustained attention. These effects were observed for both low and high caffeine consumers. The two groups did not differ at baseline, suggesting that caffeine withdrawal, which would be greater in the higher consumers, had little effect