The alerting effects of caffeine, bright light and face washing after a short daytime nap

Objective: The present study examined whether the combination of a short daytime nap with caffeine, bright light and face washing was effective against mid-afternoon sleepiness. Methods: Ten young healthy adults participated in 5 experimental conditions; those experiments were—Nap only: taking a 20 min nap; Caffeine+Nap: taking 200 mg of caffeine followed by a nap; Nap+Bright-light: being exposed to 2000 lx of bright light for 1 min immediately after napping; Nap+Face-washing: washing their faces immediately after napping; and No-Nap: taking a rest without sleep. These naps were taken at 12:40 hours. The subjects engaged in computer tasks for 15 min before napping and for 1 h after napping. Results: Caffeine+Nap was the most effective for subjective sleepiness and performance level; its effects lasted throughout 1 h after napping. Nap+Bright-light was comparable with Caffeine+Nap, except for performance level. Nap+Face-washing showed mild and transient effects, however, it suppressed subjective sleepiness immediately after napping. Conclusions: The effects of a short nap against mid-afternoon sleepiness could be enhanced by combining caffeine intake, exposure to bright light, or face washing. Significance: The present study would provide effective countermeasures against mid-afternoon sleepiness and sleepiness related accidents.