Sleep and the Hypothalamic-Pituitary-Adrenocortical Activity: Biological Processes Associated with Psychosocial Adjustment During Childhood and Adolescence Inauguraldissertation

Sleep and the hypothalamic-pituitary-adrenocortical (HPA) activity are two biological processes that play a vital role for physical and mental health as well as general well-being. The aim of this cumulative dissertation containing three studies is to complement and extend existing research on the role of sleep and the HPA activity for psychosocial adjustment during childhood and adolescence, as well as in very preterm children and to further extend knowledge on in-home PSG sleep. Taken together, findings showed that less restorative sleep and a shorter sleep duration were associated with poorer psychosocial adjustment during middle childhood and adolescence. A meditational model further showed that less restorative sleep partially accounted for poorer psychosocial adjustment in very preterm children. In adolescence, the association of sleep and psychosocial adjustment was mediated by daytime tiredness and behavioral persistence and furthermore, a delayed school start time was associated with longer sleep duration and less daytime tiredness. Additionally, a blunted HPA activity was related to more externalizing problems. Although very preterm children showed a faster decline in evening cortisol levels compared to full-term children, HPA activity did not mediate the association between prematurity and psychosocial adjustment. Furthermore, findings showed that sleep assessed via in-home PSG remained stable over one and a half years and thus indicated that in-home PSG constitutes a reliable measure of children’s habitual sleep. The present dissertation emphasizes the importance of restorative and sufficient sleep for psychosocial adjustment during middle childhood and adolescents and even more so in very preterm children representing a population of children at risk for poor psychosocial adjustment. SLEEP, HPA ACTIVITY, AND PSYCHOSOCIAL ADJUSTMENT 7