Which is better for a teen who can’t get the recommended amount of rest: just 6.5 hours of sleep at night, or 5 hours at night plus a nap in the afternoon?
These different sleep schedules may have dissimilar effects on cognition and glucose levels, say researchers.
The handful of studies that have 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 diabetes risk.
The researchers measured cognitive performance and glucose levels in students ages 15 to 19 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,” says Michael Chee, director of the Centre for Cognitive Neuroscience, a professor in the neuroscience and behavioral disorders program at 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,” Chee adds.
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 2 of 3 blood glucose levels to the standardized glucose load in both simulated school weeks,” notes Joshua Gooley, associate professor in the neuroscience and behavioral disorders program, principal investigator at the Centre for Cognitive Neuroscience, and the senior coauthor of the 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.
The findings appear in the journal SLEEP.