Sleepiness/alertness on a simulated night shift schedule and morningness-eveningness tendency

This study examined the influence of morningness-eveningness on night shift sleepiness in 15 subjects. Sleepiness was assessed during a five-night protocol involving the multiple sleep latency test (MSLT), repeated test of sustained wakefulness (RTSW) and the Stanford Sleepiness Scale (SSS). Daytime sleep was estimated by sleep diaries and wrist actigraphy. The sample was divided by median score on the Horne and Ostberg Morningness-Eveningness Questionnaire. Physiological sleep tendency was significantly worse between 0030 and 0430 hours for the Morning Tendency group than for the Non-Morning Tendency group. The Morning Tendency group reported obtaining less daytime sleep than the Non-Morning Tendency group; however, there was no difference between groups in total daytime sleep estimated by actigraphy. This preliminary study suggests that morning types are sleepier during night shift hours than non-morning types.