['Sleep loss has repeatedly been suggested to affect glucose metabolism adversely, raising the question as to the impact of subtle forms of sleep loss.', 'The aim of the study was to assess the effects of a single night of sleep restriction to 4.5 h on endocrine parameters of glucose metabolism.', 'We conducted crossover, balanced experiments including two conditions, i.e. one night of 4.5 h and one night of 7 h of sleep.', 'In 10 healthy men, circulating concentrations of insulin, C-peptide, epinephrine, norepinephrine, GH, ACTH, cortisol, and glucagon were measured after sleep and sleep restriction, respectively, during basal rest and a subsequent stepwise hypoglycemic clamp.', 'Mild sleep restriction induced a robust reduction in basal plasma glucagon levels that persisted throughout the hypoglycemic clamp (P < 0.03). Basal glucose, insulin, and C-peptide levels were unaffected by sleep restriction. Also, basal and hypoglycemia-stimulated concentrations of epinephrine, norepinephrine, and GH were unchanged after sleep restriction. Concentrations of ACTH (P < 0.05) and cortisol (P < 0.001) were reduced after sleep loss during baseline and at the start of hypoglycemia, but reached roughly comparable levels in both conditions at the end of the clamp (ACTH, P > 0.06; cortisol, P > 0.93).'] Does mild sleep restriction acutely reduce plasma glucagon levels in healthy men?