Five-hour sleep restriction for 7 days increases subjective sleepiness

We investigated the effects of a 5-h sleep restriction for 7 d on subjective sleepiness in an ambulatory condition by comparing them with baseline conditions consisting of an 8-h sleep for 7 consecutive days. Subjects were 13 healthy male students (mean age 21.1 yr). Each subject was required to get 8 h of sleep (baseline, from 2300 to 0700) for 7 d, and 5 h of sleep (sleep restriction, from 0100 to 0600) for 7 d in an ambulatory condition. The order of the two sleep schedules was randomly assigned. Subjective sleepiness was assessed by a Visual Analog Scale (VAS) every 3 h at 0900, 1200, 1500, 1800, and 2100 for 7 successive days during each sleep schedule. The VAS score during sleep restriction gradually increased up to the 5th day and then reached a plateau. The patterns of time-course changes in the VAS score were similar to those at baseline. The VAS scores showed a peak at 0900, taking a dip at 1200, and then gradually increasing toward 2100. The mean VAS score of the last three days of the 5-h sleep restriction was significantly higher than that at baseline (p<0.001). A 5-h sleep restriction for 7 d in an ambulatory condition increased subjective sleepiness up to the 5th day and then reached a plateau. The patterns of the time-course changes in sleepiness of 5-h sleep restriction per day did not differ from that at baseline.