Cortisol Awakening Response and Nighttime Salivary Cortisol Levels in Healthy Working Korean Subjects

PURPOSE Cortisol awakening response (CAR) and nighttime cortisol levels have been used as indices of adrenocortical activity. However, population-based statistical information regarding these indices has not been provided in healthy subjects. This study was carried out to provide basic statistical information regarding these indices. MATERIALS AND METHODS Cortisol levels were measured in saliva samples collected immediately upon awakening (0 min), 30 min after awakening and in the nighttime on two consecutive days in 133 healthy subjects. RESULTS We determined the mean [standard deviation (SD)], median (interquartile range) and 5th-95th percentile range for each measure and auxiliary indices for CAR, i.e., the secreted cortisol concentration within 30 min of awakening (CARscc) and absolute and relative increases in cortisol level within 30 min of awakening (CARi and CARi%, respectively). We also determined these values for auxiliary indices derived from nighttime cortisol level, i.e., the ratio of cortisol level 30 min after awakening (CA(₃₀ min)) to nighttime level (CA(₃₀ min)/NC), as well as absolute and relative decreases in cortisol levels from CA(₃₀ min) to nighttime (DCd and DCd%, respectively). We found no significant differences in cortisol level for any time point or in auxiliary indices between collection days, genders and ages. CONCLUSION The provided descriptive information and statistics on the CAR and nighttime cortisol level will be helpful to medical specialists and researchers involved in hypothalamus- pituitary-adrenal axis assessment.