Peak Cortisol Level in Shift Work Disorder
In patients with shift work disorder, there is no reliable peak cortisol level as the normal circadian rhythm of cortisol secretion is disrupted, making late night salivary cortisol (LNSC) testing inappropriate for these individuals. 1
Normal Cortisol Rhythm vs. Shift Work Disruption
- In healthy individuals with normal day-night cycles, cortisol typically peaks in the morning after waking up and declines throughout the day, reaching its lowest levels during nighttime sleep 2
- Shift work disorder disrupts the normal sleep/wake cycle, causing desynchronization of natural biological rhythms including cortisol secretion 3
- The normal circadian nadir of cortisol secretion is lost in shift workers, particularly those working night shifts 1
Cortisol Patterns in Shift Workers
- Night shift workers show blunted cortisol profiles during both night work periods and days off 4
- Female hospital employees on night shifts demonstrate altered cortisol profiles with lower levels when higher levels would typically be necessary for work activities, and higher levels at bedtime after a night shift 2
- Morning-oriented chronotypes experience larger cortisol output during night shifts, reflecting greater circadian misalignment between biological and working rhythms 5
Testing Considerations
- Late night salivary cortisol (LNSC) testing should not be performed in patients with disruption of the normal day/night cycle, such as night-shift workers 1
- The dexamethasone suppression test (DST) is the preferred diagnostic test for evaluating cortisol status in shift workers and patients with disrupted circadian rhythm due to uneven sleep schedules 1
- Cortisol awakening response (CAR) is significantly smaller after day sleep (following night shifts) than after night sleep (following day shifts) 6
Adaptation and Recovery Patterns
- Personnel typically adapt to night shift within a week regardless of schedule, but recovery from night shift takes longer time 3
- After consecutive night shifts, cortisol rhythms may not be completely readapted to normal values after one week at home 3
- Individuals with larger cortisol output during night shifts also display higher cortisol secretion on non-working days, suggesting persistent disruption of the HPA axis 5
Clinical Implications
- Chronotype (morning vs. evening orientation) affects cortisol secretion patterns in shift workers and should be considered when evaluating cortisol status 5
- Dysfunctional coping styles at work are associated with altered cortisol output during night shifts 5
- For shift workers requiring cortisol evaluation, the timing of sample collection should be adjusted according to their work pattern rather than standard time-based protocols 1