To investigate the effects of caffeine on psychomotor vigilance and sleepiness during sleep restriction and following subsequent recovery sleep.
Participants were N=48 healthy good sleepers. All participants underwent 5 nights of sleep satiation [time-in-bed (TIB): 10 hrs], followed by 5 nights of sleep restriction (TIB: 5 hrs), and 3 nights of recovery sleep (TIB: 8 hrs) in a sleep laboratory. Caffeine (200 mg) or placebo was administered in the form of chewing gum at 0800 and 1200 hrs each day during the sleep restriction phase. Participants completed hourly 10-min psychomotor vigilance tests (PVTs) and a modified Maintenance of Wakefulness Test approximately every 4 hours during the sleep restriction and recovery phases.
Caffeine maintained objective alertness compared to placebo across the first three days of sleep restriction, but this effect was no longer evident by the fourth day. A similar pattern of results was found for MWT sleep latencies, such that those in the caffeine group (compared to placebo) did not show maintenance of wakefulness relative to baseline after the second night of restriction. Compared to placebo, participants in the caffeine condition displayed slower return to baseline in alertness and wakefulness across the recovery sleep period. Lastly, the caffeine group showed greater N3 sleep duration during recovery.
Caffeine appears to have limited efficacy for maintaining alertness and wakefulness across 5 days of sleep restriction. Perhaps more importantly, there may be recovery costs associated with caffeine use following conditions of prolonged sleep loss.