Compensating Fatigue by Caffeine

Caffeine is said to have, non-specific arousal enhancing effects and specific cognitive effects (Van der Stelt & Snel, 1993, 1998). If true, especially in states of fatigue the energising effects of caffeine should be found more prominently. The antihypnoid or fatigue compensating effects of moderate amounts of caffeine, appear to be caused predominantly by the blocking of inhibitory adenosine receptors which are found diffusely distributed in the brain. It implies that effects of caffeine will be seen as increases of cortical arousal. Indeed, caffeine has been found to induce increased cortical arousal, manifested as increasein frequency in the EEG. Also, after ingesting caffeine doses up to 250 mg caffeine, subjects report a decrease of fatigue, sleepiness or drowsiness, increased alertness or more vigour (e.g. Koopmans & Van Boxtel, 1988; Reyner & Horne, 1997). Bonnet and Arand (1992) used caffeine to develop a physiological arousal model of chronic insomnia in a group of healthy adults. The subjects received three times daily 400 mg caffeine for 7 nights and days. In addition to a reduced sleep efficiency, sleepiness during day time, as measured with the MSLT, was significantly increased (cf. Koopmans & Van Boxtel, 1988). Obviously, arousing effects of caffeine at night may cause increased sleepiness during daytime.