The title of the post is a copy and paste from the title and first paragraph of the linked academic press release here:
We found that compared to being able to sleep 9 hours a night, having only 6.5 hours to sleep in 24 hours degrades performance and mood. Interestingly, under conditions of sleep restriction, students in the split sleep group exhibited better alertness, vigilance, working memory and mood than their counterparts who slept 6.5 hours continuously.
June C Lo, Derek C K Twan, Swathy Karamchedu, Xuan Kai Lee, Ju Lynn Ong, Elaine van Rijn, Joshua J Gooley, Michael W L Chee.
Differential Effects of Split and Continuous Sleep on Neurobehavioral Function and Glucose Tolerance in Sleep-Restricted Adolescents.
Many adolescents are exposed to sleep restriction on school nights. We assessed how different apportionment of restricted sleep (continuous versus split sleep) influences neurobehavioral function and glucose levels.
Adolescents, aged 15-19 years, were evaluated in a dormitory setting using a parallel-group design. Following 2 baseline nights of 9-h time-in-bed (TIB), participants underwent either 5 nights of continuous 6.5-h TIB (n=29) or 5-h nocturnal TIB with a 1.5-h afternoon nap (n=29). After 2 recovery nights of 9-h TIB, participants were sleep restricted for another 3 nights. Sleep was assessed using polysomnography (PSG). Cognitive performance and mood were evaluated 3 times per day. Oral Glucose Tolerance Tests (OGTT) were conducted on mornings after baseline sleep, recovery sleep, and the third day of each sleep restriction cycle.
The split sleep group had fewer vigilance lapses, better working memory and executive function, faster processing speed, lower level of subjective sleepiness, and more positive mood, even though PSG-verified total sleep time was less than the continuous sleep group. However, vigilance in both sleep-restricted groups was inferior to adolescents in a prior sample given 9-h nocturnal TIB. During both cycles of sleep restriction, blood glucose during the OGTT increased by a greater amount in the split sleep schedule compared with persons receiving 6.5-h continuous sleep.
In adolescents, modest multi-night sleep restriction had divergent negative effects on cognitive performance and glucose levels depending on how the restricted sleep was apportioned. They are best advised to obtain the recommended amount of nocturnal sleep.