Self-Reported Sleep Duration, Daytime Sleepiness, and Caffeine Use in Male and Female Morning and Evening Types

Abstract

INTRODUCTION Morningness-eveningness (ME) is defined as the diurnal preference, and it reflects individual differences in the preferred time of activity revealed by general behavioral patterns, including sleep timing. 1 The temporal misalignment between endogenous circadian rhythms and the timing of the sleep-wake cycle has been hypothesized to have a negative influence on sleep. Such a mismatch is mainly found in evening type (ET) subjects, who prefer late bedtimes and wake times, and who in many cases have shortened sleep on weekdays because of the need to wake early for school or work. 2-4 There are several reports that ET subjects have a shorter sleep duration on work days, 2,4,5 and sleep duration becomes shorter as the work times move earlier. 6 In addition to having shorter sleep on weeknights, ET individuals may have other characteristics such as irregular sleep habits and/or an excessive need for sleep that can impact their sleep quality in a negative way. 4 In a previous study of factors that affect sleep quality, 7 evening preference was a better predictor of poor sleep quality than job characteristics such as shift work or life pattern. Furthermore, these differences in sleep habits between ME types are associated with other behaviors that suggest ET individuals have a sleep deficit, including greater caffeine Background and ObjectiveaaPrevious studies in adults have focused on differences in sleep timing with respect to morning and evening (ME) types, or gender difference in the distribution of ME types. We aimed to examine sleep habits and behaviors (daytime sleepi-ness and caffeine consumption) of adult ME types, and to examine whether the factors associated with ME type differed between men and women.