Reciprocal relations between objectively measured sleep patterns and diurnal cortisol rhythms in late adolescence

Purpose: To examine how hours of sleep and wake times relate to between-person differences and day-to-day changes in diurnal cortisol rhythms in late adolescence. Methods: Older adolescents (N = 119) provided six cortisol samples (wakeup, +30 minutes, +2 hours, +8 hours, +12 hours, and bedtime) on each of three consecutive days while wearing an actigraph. We examined how average (across 3 days) and day-to-day changes in hours of sleep and wake times related to diurnal cortisol patterns. Results: On average, more hours of sleep related to steeper decline in cortisol across the days. Day-to-day analyses revealed that the hours of sleep of the previous night predicted steeper diurnal slopes the next day, whereas greater waking cortisol levels and steeper slopes predicted more hours of sleep and a later wake time the next day. Conclusion: Our results suggest a bidirectional relationship between sleep and hypothalamic-pituitary-adrenal axis activity.