Summary: Researchers report different sleep schedules with the same amount of total sleep time impact the teenage brain differently. Those who nap in the afternoon, but sleep less at night, have higher levels of blood glucose than those who sleep longer at night, the study reports.
Source: Duke NUS Medical School.
Many adolescent students sleep less than the recommended duration of 8-10 hours a night. It is unclear; however, whether short night sleep combined with an afternoon nap is as good as having the same amount of sleep continuously during the night without a nap. Researchers at Duke-NUS Medical School have demonstrated for the first time that different sleep schedules with the same total sleep opportunity over 24 hours may have dissimilar effects on cognition and glucose levels. This is the first study to gather experimental evidence on the notion that ‘what may be appropriate sleep for one health goal may not be for another’.
The handful of studies that examined split sleep schedules with normal total sleep duration in working-age adults found that both schedules yield comparable brain performance. However, no study has looked at the impact of such schedules on brain function and glucose levels together, especially when total sleep is shorter than optimal. The latter is important because of links between short sleep and risk for diabetes.
The researchers measured cognitive performance and glucose levels following a standardized load in students, aged 15-19 years, during two simulated school weeks with short sleep on school days and recovery sleep on weekends. On school days, these students received either continuous sleep of 6.5 hours at night or split sleep (night sleep of 5 hours plus a 1.5-hour afternoon nap).
“We undertook this study after students who were advised on good sleep habits asked if they could split up their sleep across the day and night, instead of having a main sleep period at night,” said Prof. Michael Chee, Director of the Centre for Cognitive Neuroscience, Professor of Neuroscience and Behavioral Disorders Programme, Duke-NUS Medical School and one of the study’s senior authors. “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. This finding is remarkable as the measured total sleep duration over 24 hours was actually less in the former group”, Prof. Chee added.
However, for glucose tolerance, the continuous schedule appeared to be better. “While 6.5 hours of night sleep did not affect glucose levels, the split sleep group demonstrated a greater increase in blood glucose levels to the standardized glucose load in both simulated school weeks,” noted Dr. Joshua Gooley, Associate Professor of Neuroscience and Behavioral Disorders Programme, Principal Investigator at the Centre for Cognitive Neuroscience, Duke-NUS Medical School and the senior co-author of this study.
Although further studies are necessary to see if this finding translates to a higher risk of diabetes later in life, the current findings indicate that beyond sleep duration, different sleep schedules can affect different facets of health and function in directions that are not immediately clear.
Professor Patrick Casey, Senior Vice Dean of Research, Duke-NUS Medical School, commented, “Recent sleep surveys show that Singaporeans are among the world’s most sleep deprived people. This is the latest in a series of studies from a team of researchers from the Neuroscience and Behavioural Disorders Programme and Centre for Cognitive Neuroscience that have provided valuable insights into the importance of good sleep.”
Source: Lekshmy Sreekumar – Duke NUS Medical School
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Original Research: Open access research for “Differential Effects of Split and Continuous Sleep on Neurobehavioral Function and Glucose Tolerance in Sleep-Restricted Adolescents” by June C Lo, PhD, Derek C K Twan, BSocSc, Swathy Karamchedu, MBBS; MS, Xuan Kai Lee, BSc, Ju Lynn Ong, PhD, Elaine van Rijn, PhD, Joshua J Gooley, PhD, and Michael W L Chee, MBBS in Sleep. Published February 12 2019.
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.