In this study, cortisol levels among day shift nurses showed normal circadian rhythm despite work stress; however,
night workers demonstrated apparent disruption in the circadian pattern. Our results indicate that 16 h night shift work demonstrated marked circadian misalignment.
Cortisol secretion is known to show a distinct diurnal pattern with the highest level in the morning and lowest at night [5] [8]. Shift workers, particularly night workers, are reported to suffer impaired circadian rhythm of
cortisol release [9]. In this study, cortisol levels of day shift nurses showed normal diurnal fluctuations, but the
kinetic changes observed among night shift nurses indicated that their bodies adjusted to the start of the night
shift as if they were operating in the morning