Cortisol awakening response and nighttime salivary cortisol levels in healthy working Korean subjects

Abstract

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.

Fig. 1

Cortisol levels immediately upon awakening (A), 30 min after awakening (B), and at nighttime (C). Cortisol levels were determined from saliva samples collected immediately upon, 30 min after awakening and at nighttime from 133 healthy subjects over two consecutive days. The data at each time point was pooled for the two consecutive days. Boxes represent the interquartile range (IQR), whiskers represent the 5th-95th percentile range, and outliers are represented by closed circles. Horizontal lines and the cross symbol within the boxes represent the median and mean cortisol values, respectively.