The impacts of sleep variability on mental health and cognitive functioning in children, adolescents and young adults

Abstract

There is much evidence suggesting the negative health-related consequences of sleep restriction and poor sleep quality across the life span. However, the effects of variable sleep-wake schedule on daytime functioning remain less clear, especially in the young populations. This thesis aimed to evaluate the impacts of variability in sleep timing and sleep duration on academic performance, mental health and cognitive functioning in children, adolescents and young adults. Chapter 2 consists of a systematic review and meta-analysis of 69 studies examining the associations of weekday-to-weekend sleep discrepancy (i.e., social jetlag and catch-up sleep) on academic performance and health-related outcomes in school-age children and adolescents. There was evidence to support the associations of social jetlag with poor academic performance, substance use and the risk of overweight/obesity. Meanwhile, weekend catch-up sleep was associated with poor academic performance, depressive symptoms and substance use. Chapter 3 reported a community-based cross-sectional study to examine the associations of social jetlag and chronotype with insomnia symptoms as well as emotional and behavioural problems in a sample of 547 school-age children. Evening chronotype and social jetlag were both associated with insomnia symptoms. In addition, evening chronotype was associated with externalising symptoms after controlling for insomnia. In Chapter 4, 122 secondary school students and 115 college students were recruited to undergo a comprehensive assessment of their sleep, mood and cognitive functioning, including a 7-day prospective actigraphic monitoring of sleep-wake pattern, followed by a section of neurobehavioural tests to measure daytime sleepiness, mood and cognitive performance. Greater social jetlag was associated with poorer selective attention and greater catch-up sleep was associated with poorer cognitive flexibility in the secondary school students with insufficient sleep. Greater catch-up sleep was related with higher daytime sleepiness in college students with insufficient sleep. Meanwhile, greater weekend catch-up sleep showed an overall association with lower negative mood in college students. No significant association of day-to-day sleep variability with impaired daytime functioning was found. Chapter 5 presents an experimental study, in which young adults were recruited and instructed to sleep in the laboratory on a variable schedule over 6 consecutive nights, alternating between 6h and 9h of time-in-bed each night with fixed daily rise time. Comprehensive assessments were conducted at baseline (with 7.5h of normal sleep) and during the experimental period with variable sleep schedule, including objective sleep assessments by polysomnography and actigraphy, and a battery of neurobehavioural tests and heart rate variability measures performed in every morning and evening. Results showed a decrement in cognitive performance (sustained attention) as result of the experimentally-induced sleep variability. Decreased sleep quality was observed during the experimental period as evident by increased sleep onset latency and wake after sleep onset. Slow wave sleep, daytime cardiac autonomic control and diurnal secretion of cortisol were less affected by sleep variability. In summary, sleep discrepancy/variability is associated with a constellation of negative health-related outcomes, especially in young people. The interplay between sleep discrepancy/variability and other sleep and circadian features may also impact on daytime functioning in children, adolescents and young adults.