Variability in cortisol awakening response related to sleep efficiency and its relationship with trait anxiety and psychological resilience

The relationship between the cortisol awakening response (CAR) and individual mental health remains debated. To address this, the present study introduces CAR variability across multiple days as a novel indicator, aiming to resolve inconsistencies in prior findings often caused by situational factors affecting the traditional mean CAR measure. We investigate the association between CAR variability and both trait anxiety and psychological resilience. In Experiment 1, we reduced CAR variability by minimizing sleep efficiency variation under natural sleep conditions, finding a significant positive correlation between CAR variability and trait anxiety scores. This suggests that lower CAR variability in stable conditions correlates with lower trait anxiety. In Experiment 2, CAR variability was increased through total sleep deprivation, revealing a significant positive correlation between CAR variability and psychological resilience. This indicates that greater CAR variability in dynamic conditions corresponds with higher psychological resilience. In contrast, CAR mean levels across both experiments showed no significant associations with either trait anxiety or psychological resilience. These findings suggest that, beyond mean CAR levels, CAR variability may serve as a more effective physiological indicator of mental health. Considering CAR variability across multiple days is crucial for understanding how individuals adapt to daily life stressors and challenges, providing new perspectives and potential avenues for promoting mental health and developing effective intervention strategies.