Understanding the impact of sleep duration on cortisol awakening response during early adulthood

Abstract

Background : The impact of sleep on basal Hypothalamic–Pituitary–Adrenal (HPA)-axis functioning has been well documented. Specifically, decreased sleep quality and quantity are associated with higher basal cortisol levels, one index of HPA-axis functioning. Few studies, however, have examined the impact of sleep quality and quantity on the cortisol awakening response (CAR), or the diurnal peak in cortisol that occurs shortly after awakening. Investigating this association is important given that a higher CAR is associated with an increased risk for mental and physical health problems. Therefore, the current study aims to further examine the relationship between sleep and CAR in order to gain a better understanding of sleep's impact on HPA-axis functioning. Methods : 58 undergraduate students (29 males; mean age = 18.74) were assessed over two consecutive mornings. Each morning, participants completed a daily sleep diary to assess self-reported sleep quality and total sleep time (TST) from the previous night. Saliva samples were used to obtain morning cortisol levels. Participants were asked to provide four saliva samples by spitting into salivettes. The first sample was obtained immediately after awakening. The following three samples were obtained at 30, 45, and 60 minutes after the first sample. Participants repeated this procedure on Day 2. Results : Multilevel growth curve modeling was used in order to examine the impact of sleep quality and quantity on CAR. Results from the current study demonstrate that TST, or the total minutes slept during the preceding night on each day was significantly associated with both the intercept and slope of the model. More specifically, lower TST was associated with lower cortisol levels at awakening (t=5.40, p<0.0001), but a steeper post-awakening cortisol slope (t= − 2.55, p=0.01). After accounting for TST, however, sleep quality did not significantly predict any parameters in the model. Conclusions : Contrary to prior research that has reported no or a small association between sleep duration and CAR, our study shows that participants with shorter sleep duration have lower cortisol levels at awakening and a faster rate of cortisol increase following awakening. Thus, these findings suggest that the amount a person sleeps may directly impact their diurnal cortisol pattern the subsequent morning.

Keywords

• HPA axis
• cortisol
• sleep
• college students