Recent evidence suggests that the cortisol awakening response (CAR) on any single day is determined by a combination of trait and state factors; however, the nature of such state associations remains largely unexplored. In this study we examined day-to-day changes in the CAR and their covariance with simultaneous changes in sleep-related variables, alcohol consumption, and motility levels. We employed a novel approach to this field of research in the form of a detailed case study of a 27-year-old healthy male (TS) over 50 measurement days, occurring at 3-day intervals. On each measurement day, salivary free cortisol was determined at 0, 15, 30, and 45 min post-awakening and sleep-related variables, alcohol consumption on the previous evening, and post-awakening motility were measured.
Our findings show considerable day-to-day variability in the CAR, particularly the dynamic increase, which averaged 17.2 nmol/l and ranged from 3.6 to 39.0 nmol/l (max–min values). We also report a strong relationship between changes in awakening time and changes in the first waking sample (explaining ∼38% of its variability) such that later awakening was associated with a higher first waking sample. This relationship was found to be stronger on days when awakening time was earlier in the morning than on days when it was later. Our findings also provide a preliminary indication for an inverse association between alcohol consumption on the evening before a sampling day and the dynamic of the AUCI, while no associations between sleep quality, post-awakening motility levels, and mode of awakening and measures of the CAR were found.