Diurnal preference, sleep habits, circadian sleep propensity and melatonin rhythm in healthy human subjects

After 24-h sleep deprivation, 33 healthy you ng subjects entered the 10/20 min ultra-shore sleep-wake schedule for 26 h. Melatonin rhythm was hourly assessed simultaneously. Results indicated that morning preference was significantly correlated with habitual sleep onset (r = -0.41, P = 0.04), habitual sleep offset (r = -0.52, P = 0.002), melatonin peak time (r = -0.36, P = 0.04), and sleep propensity onset time (r = -0.36, P = 0.04). The intervals between habitual sleep mid-point and melatonin peak time and between habitual sleep mid-point and sleep propensity onset time were significantly longer in morning-preference subjects than in evening-preference subjects (P < 0.05). These findings suggest that the variance of diurnal preference may be related to differences in phase relations between habitual sleep timing and the circadian pacemaker. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.