Caffeine and long hours of work: effects on alertness and simple reaction time

Abstract

Background: The effects of caffeine on cognition and alertness are well-documented. One established effect of caffeine is that it restores function when the person has a low level of alertness. This topic was examined here, with alertness being reduced by prolonged work. The effects of caffeine were assessed by two measures known to be sensitive to fatigue, namely subjective alertness and simple reaction time. The study also examined whether effects could be attributed to the reversal of caffeine withdrawal and whether decaffeinated coffee also had beneficial effects. Methods: Each participant carried out three twelve-hour sessions (from 9.00 to 21.00). The first eight hours were constant and involved four test batteries and consumption of water at the breaks. On one of the days, participants were given caffeinated coffee (3mg/kg) after eight hours, followed by another test battery, another dose of caffeine at ten hours, followed by the final test session. On the other days, volunteers were given juice or decaffeinated coffee. Twenty-four students (12 male) took part in the study. Results: The results showed that caffeine was associated with higher alertness scores and faster simple reaction times. The effects of caffeine increased from the first dose to the second. There were no differences between the decaffeinated coffee and the juice conditions. Conclusion: These results demonstrate that caffeine is beneficial in low arousal situations. The results could not be attributed to the reversal of caffeine withdrawal as effects were still observed following a prior dose of caffeine. Decaffeinated coffee had no significant effects. These results have important implications for real-life situations involving prolonged work and show that caffeine is an effective countermeasure to fatigue.