Objectives This study aims to investigate the correlation between cortisol awakening response (CAR) and sleep quality, mental stress, fatigue, workload and health status in a period of 28 days.

Materials and Methods A total of 28 subjects participated in this study. The saliva was collected by cotton-based Salivette at awakening, 30 min after awakening, and bedtime for a period of 4 weeks. The saliva cortisol was measured by LC-MS-MS. Four parameters were used to present CAR, 30 min post-awakening cortisol, CAR denoting rise from awakening to 30 min post-awakening (slope), AUC for CAR, and full AUC (= AUC for CAR + AUC for late decline). The outcomes variables included sleep quality measured by Pittsburgh sleep quality index (PSQI) questionnaire, and self-rated workload, mental stress, fatigue, and health score for each day.

Results CAR were correlated with fatigue score and stress score, but not with sleep quality (PSQI), workload and health score. Regarding parameters of CAR, AUC for CAR and full AUC are better than CAR slope and 30 min post-awakening to correlate with fatigue and stress. AUC for CAR and full AUC may represent the degree of mental stress and fatigue in the previous day.

Discussion We have found single day CAR and 4 week CAR were correlated with mental stress. But how to design a study to elaborate whether CAR can predict the occurrence of cardiovascular diseases (Karoshi) needs further to be solved. Solution for variation of CAR day-to-day and pick-up the day of most stressful are urgent.