SUMMARYThe present study sought to investigate whether a single night of partial sleep deprivation (PSD) would alter fasting insulin sensitivity and cephalic phase insulin release (CPIR) in humans. A rise in circulating insulin in response to food-related sensory stimulation may prepare tissues to break down ingested glucose, e.g. by stimulating rate-limiting glycolytic enzymes. In addition, given insulin's anorexigenic properties once it reaches the brain, the CPIR may serve as an early peripheral satiety signal. Against this background, in the present study 16 men participated in two separate sessions: one night of PSD (4.25 h sleep) versus one night of full sleep (8.5 h sleep). In the morning following each sleep condition, subjects' oral cavities were rinsed with a 1-molar sucrose solution for 45 s, preceded and followed by blood sampling for repeated determination of plasma glucose and serum insulin concentrations (À3, +3, +5, +7, +10 and +20 min). Our main result was that PSD, compared with full sleep, was associated with significantly higher peripheral insulin resistance, as indicated by a higher fasting homeostasis model assessment of insulin resistance index (+16%, P = 0.025). In contrast, no CPIR was observed in any of the two sleep conditions. Our findings indicate that a single night of PSD is already sufficient to impair fasting insulin sensitivity in healthy men. In contrast, brief oral cavity rinsing with sucrose solution did not change serum insulin concentrations, suggesting that a blunted CPIR is an unlikely mechanism through which acute sleep loss causes metabolic perturbations during morning hours in humans. IN TROD UCTI ONIn humans, partial sleep deprivation (PSD) for a duration lasting from 1 day to 1 week has been linked to impaired postprandial glucose disposal (Buxton et al., 2010;Donga et al., 2010;Schmid et al., 2011;Spiegel et al., 1999; also reviewed in Cedernaes et al., 2015a), possibly as a result of insulin resistance (Broussard et al., 2012(Broussard et al., , 2015 and tissuespecific clock disruption (Cedernaes et al., 2015b). In contrast, evidence for the effects of PSD on fasting circulating concentrations of insulin and glucose are less conclusive. For instance, a recent study involving 21 male adolescents revealed that three consecutive nights of PSD (4 h night À1 ) increased fasting insulin resistance-as assessed by the fasting homeostasis model assessment of insulin resistance (HOMA-IR) index (Matthews et al., 1985)-by approximately 59%, compared with values obtained after three nights of unrestricted sleep (Klingenberg et al., 2013). Studies exploring the metabolic effects of one night of PSD in adults did not, however, reveal such fasting insulin resistance-promoting effects of PSD (e.g. Donga et al., 2010). These controversial findings thus warrant further investigation into the acute effects of PSD on fasting insulin resistance in humans.Another aspect of human insulin metabolism that has not been investigated thoroughly in relation to PSD is the cephalic phase insulin ...

The findings suggest that 8-h sleep duration, within the range recommended by the US National Sleep Foundation, may not only help consolidate newly learned procedural and declarative memories, but also ensure full access to both during periods of subjective stress.

Our findings suggest that learning in the evening and subsequent sleep-dependent consolidation of procedural and spatial memories are unaltered in young men living under a fixed short sleep schedule. Future studies are warranted to validate our findings in other groups (e.g. adolescents and older subjects) and after more prolonged chronic sleep loss paradigms.