Abstract

Dr. Andrew P. Smith PhD*

ABSTRACT

Background: The effects of caffeine on 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 at a low level due to time of day (early morning). The effects of caffeine were assessed by measuring subjective alertness, hedonic tone, anxiety and a symptom checklist. The study also examined whether effects could be attributed to the reversal of caffeine withdrawal. Methods: Three groups of participants were recruited: non-consumers of caffeine (N=23); low consumers (<200mg/day; N=40) and high consumers (>300mg/day; N=33). After overnight caffeine abstinence participants visited the laboratory and rated their mood and current symptoms. They then consumed a fruit juice which had either caffeine (100 mg) or placebo added. Two hours later, they returned to the laboratory and repeated their subjective ratings. They repeated this procedure on five consecutive days. Results: Caffeine was associated with significantly higher alertness. This effect did not change over days. No effects of withdrawal were observed in the baseline ratings. The effect of caffeine on alertness was present in consumers and non-consumers. There were no significant effects of caffeine on hedonic tone, anxiety or a symptom checklist. Conclusion: These results demonstrate that caffeine is beneficial in low arousal situations, in this case when circadian alertness is increasing. This effect was reliable in that it did not change across the five day period. The results could not be attributed to the reversal of caffeine withdrawal, as no effects of withdrawal were present at baseline, and increased alertness after caffeine was observed in non-consumers and withdrawn consumers. The significant effects of caffeine were specific to alertness rather than mood or subjective ratings per se. These results have important implications for real-life situations involving low arousal states and show that caffeine is an effective countermeasure when circadian alertness is low.