O033 Is Sleeping and Waking Important for the Cortisol Awakening Response?

INTRODUCTION: The rapid rise in cortisol after waking is known as the cortisol awakening response (CAR). However, as part of its normal circadian rhythm cortisol also rises in the morning independent of awakening. If CAR is a direct response to awakening, it should be eliminated in conditions of sleep deprivation (SD). Given that an atypical CAR is associated with several psychiatric and medical disorders, understanding the factors that influence CAR is of clinical relevance. This study explored cortisol during the normal waking period prior, during, and post-SD. METHODS: N=21 (11F 22.80±4.40y) completed 62h of SD in the laboratory. Salivary cortisol was collected across 5-time-points (07:00h, 07:15h, 07:30h, and 07:45h) on 2-pre-at-home-study days, 4-in-lab-study days, and 2-post-at-home-study days. Mixed-effects ANOVAs tested for fixed effects of day, time, and their interactions on cortisol, and cortisol area under the curve (AUCi, AUCg). RESULTS: SD produced significant effects of time*day (p<0.001). Cortisol levels at +30 and +45min post-awakening were lower on SD days. Cortisol levels on awakening (0mins) did not differ between any study days. There were significant effects of day (p<0.001). AUCi and AUCg were greater on in-laboratory-baseline and recovery days compared to other study days. DISCUSSION: This study found CAR is not present during periods of SD when there is no ‘waking’ from sleep. It showed for the first time that CAR recovers to baseline levels following recovery sleep. While the role of the CAR remains unclear this study identified factors that future research should consider to advance understanding of its purpose.