Effects of dietary caffeine on mood when rested and sleep restricted

Prolonged use of caffeine can lead to physical dependence evidenced by characteristic withdrawal symptoms during abstinence. Debate exists as to whether mood enhancement by caffeine represents a net effect or merely the restoration of abstinence-induced mood decrements. One aim of this study was to determine the net effects on mood of dietary caffeine compared with prolonged abstinence. In addition, the study aimed to determine whether caffeine restores mood degraded by a non-caffeine source, namely, sleep restriction. A double-blind placebo-controlled cross-over design was employed in which 48 male and female volunteers alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while being either rested or sleep restricted. Mood was assessed using a computerized version of the profile of mood states (POMS), giving scores for overall mood and six mood dimensions. Gender had small effects on mood, whereas all mood dimensions were markedly adversely affected by sleep restriction. Caffeine had no significant net enhancing effects on mood when participants were rested, and produced no net restorative effects when mood was degraded by sleep restriction. On the contrary, caffeine-induced decrements in mood were observed during both conditions of rest and sleep restriction.