Dissecting the impact of sleep and stress on the cortisol awakening response in young adults.

Cortisol rises precipitously upon awakening, in what has been called the cortisol awakening response (CAR). Atypical CARs have been linked to a number of negative health outcomes. Yet, our understanding of the possible mechanisms creating these associations remains unclear. Both stress and sleep can influence CAR, and may potentially explain its links to health. However, these factors also impact each other, and their influence on CAR has rarely been studied simultaneously. In order to differentiate their effects, this study examined the impact of daily life hassles, anticipatory stress, and subjectively reported sleep on CAR among 58 college students. Self-reported stress and sleep, as well as salivary cortisol (collected during the first hour after awakening) were obtained across two consecutive days. Total sleep time predicted CAR magnitude, but daily hassles and anticipatory stress did not after accounting for the effect of sleep. Lower total sleep time was associated with lower awakening cortisol and greater CAR. These results provide further evidence for the impact of sleep insufficiency on CAR, and suggest future efforts to use CAR as a stress biomarker should take the impact of sleep into consideration. Published by Elsevier Ltd.