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Am J Physiol Endocrinol Metab 292: E253-E261, 2007. First published August 29, 2006; doi:10.1152/ajpendo.00651.2005
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Daytime napping after a night of sleep loss decreases sleepiness, improves performance, and causes beneficial changes in cortisol and interleukin-6 secretion

¹Sleep Research and Treatment Center, Department of Psychiatry; ²Health Evaluation Sciences, Penn State College of Medicine, Hershey, Pennsylvania; ³Reproductive Biology and Medicine Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; and ⁴First Department of Pediatrics and Unit on Endocrinology, Metabolism, and Diabetes, Athens University Medical School, Athens, Greece

Submitted 27 December 2005 ; accepted in final form 28 August 2006

Sleep loss has been associated with increased sleepiness, decreased performance, elevations in inflammatory cytokines, and insulin resistance. Daytime napping has been promoted as a countermeasure to sleep loss. To assess the effects of a 2-h midafternoon nap following a night of sleep loss on postnap sleepiness, performance, cortisol, and IL-6, 41 young healthy individuals (20 men, 21 women) participated in a 7-day sleep deprivation experiment (4 consecutive nights followed by a night of sleep loss and 2 recovery nights). One-half of the subjects were randomly assigned to take a midafternoon nap (1400–1600) the day following the night of total sleep loss. Serial 24-h blood sampling, multiple sleep latency test (MSLT), subjective levels of sleepiness, and psychomotor vigilance task (PVT) were completed on the fourth (predeprivation) and sixth days (postdeprivation). During the nap, subjects had a significant drop in cortisol and IL-6 levels (P < 0.05). After the nap they experienced significantly less sleepiness (MSLT and subjective, P < 0.05) and a smaller improvement on the PVT (P < 0.1). At that time, they had a significant transient increase in their cortisol levels (P < 0.05). In contrast, the levels of IL-6 tended to remain decreased for 8 h (P = 0.1). We conclude that a 2-h midafternoon nap improves alertness, and to a lesser degree performance, and reverses the effects of one night of sleep loss on cortisol and IL-6. The redistribution of cortisol secretion and the prolonged suppression of IL-6 secretion are beneficial, as they improve alertness and performance.

alertness; sleep deprivation; proinflammatory cytokines; hypothalamic-pituitary-adrenal axis; daytime sleep