Examining multiple sleep behaviors and diurnal patterns of salivary cortisol and alpha-amylase: within- and between-person associations
Sleep is essential for physical and psychological health. Sleep has also been linked to the daily patterns of key stress-responsive physiological systems, specifically the hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). Extant research examining sleep and diurnal patterns of cortisol, the primary end product of the HPA axis, is inconsistent. Moreover, it is not clear how specific aspects of sleep behavior (e.g., sleep duration, sleep quality, sleep variability) are related to specific components of diurnal cortisol rhythms. Salivary alpha-amylase (sAA) has been recognized as a surrogate marker of ANS activity, but limited research has explored relations between sleep and sAA diurnal rhythms. The current study utilized a modified ecological momentary assessment protocol to examine within- and between-person relations between multiple facets of sleep behavior using multiple methods (e.g., subjective report, actigraphy) and salivary cortisol and sAA. First year college students (N = 76) provided saliva samples and diary entries five times per day over the course of three days. Sleep was assessed via questionnaire, through daily diaries, and monitored objectively using actigraphy over a four day period. Between-person results revealed that shorter average sleep duration and greater sleep variability was related to lower levels of waking cortisol and flatter diurnal slopes across the day. Within-person results revealed that on nights when individuals slept for shorter durations than usual they also had lower levels of waking cortisol the next day. Sleep was not related to the cortisol awakening response (CAR) or diurnal patterns of sAA, in either between-person or within-person analyses. However, typical sleep behaviors measured via questionnaire were related to waking levels of sAA. Overall, this study provides a greater understanding of how multiple components of sleep, measured in naturalistic environments, is related to cortisol and sAA diurnal rhythms, and how day-to-day, within-person changes in sleep duration contribute to daily variations in cortisol.