The cortisol awakening response: predicting self-reported daily stress reactivity

Background and Objectives: The cortisol awakening response (CAR) refers to a phenomenon characterized by a significant increase in cortisol levels following morning awakening. Previous studies have shown that an aberrant CAR is associated with stress-related disorders. However, there is a lack of prospective longitudinal studies examining whether individual differences in the CAR can predict daily stress reactivity.Design and Methods: In a sample of 68 healthy college students (23.5% female, Mage = 18.77, SD = 0.97), saliva samples were collected at 0, 15, 30, and 45 min after awakening on three consecutive days. The participants were then asked to report their daily perceived stress and daily negative affect for a period of 30 days, 18 months later, during the COVID-19-related lockdown in the region.Results: The results indicated that a higher CAR at the beginning of the COVID pandemic was associated with lower levels of daily negative affect assessed 18 months later. Furthermore, the CAR modulated the link between daily perceived stress and negative affect. Specifically, individuals with a higher CAR were more reactive to perceived stress in their daily lives.Conclusions: The present findings provide insights into the psychobiological mechanisms that connect daily stress with mental health.