Chronotype-related sleep loss is associated with reduced amplitude in circadian rhythm and higher fragmentation of REM sleep in young health adults (Preprint)

BACKGROUND In modern society, the midpoint and duration of sleep on workdays are primarily determined by the alarm clock. Early work, especially in late chronotypes, can lead to sleep timing misalignment and reduced sleep quality on workdays. This might be one of the reasons for high incidence of sleep disorders. However, very little is known about sleep architecture under real life conditions. OBJECTIVE Our study aims to elucidate relationships between objective measures of sleep timing, circadian rhythms of sleep stages, and composition of sleep under real life conditions to better understand the discrepancy of sleep quality between workdays and days off. METHODS Participants were fitted with Fitbit Inspire trackers for 3 month and completed a questionnaire including items on sleep disturbance and tiredness on waking as a measure of low sleep quality. Objective measures of sleep timing and sleep architecture were derived from Fitbit sleep data. Objective measures of sleep timing included midpoint of sleep and sleep duration. Social jet lag and sleep loss were calculated based on the respective discrepancies between workdays and free days. Objective measures of sleep architecture included amount, proportion and fragmentation of sleep stages. In addition, phase and amplitude of circadian rhythms of the sleep stages were analysed. Correlations between the variables were calculated as a measure of the direction of relationships. RESULTS On free days, midpoint of sleep, which is a chronotype measure, was later, sleep duration was longer, and sleep quality was higher than on workdays. Consequently, chronotype correlated positively with social jet lag and sleep loss. Lower sleep quality on free days, i.e. under conditions primarily determined by the internal clock, correlated positively with sleep disturbances. Sleep loss correlated negatively with circadian rhythm stability and positively with fragmentation of REM sleep on free days. Furthermore, circadian rhythm stability of REM sleep correlated positively with the proportion of deep sleep and negatively with fragmentation of REM sleep. Sleep quality on free days, and sleep disturbance correlated negatively with proportion and positively with fragmentation of REM sleep. In summary, chronotype-related sleep loss is negatively correlated with lower robustness of circadian rhythm, lower proportion and higher fragmentation of REM sleep, which in turn are related to a general poor quality of low sleep. CONCLUSIONS Our data suggest that chronotype-induced sleep loss leads to an internal misalignment of sleep stage timing and sleep architecture, resulting in general lower quality of sleep and a higher susceptibility for sleep disturbance. This study suggests that individualized working hours could improve public health, which is of high relevance given the special opportunities arising from the conversion of many workplaces to home office caused by the Covid-19 pandemic. CLINICALTRIAL https://ethikpool.medizin.hhu.de/, registration number: 2019-3786