Summary: Cortisol, commonly called the “stress hormone,” usually falls to its lowest level around midnight so the body can rest and repair. New research, however, shows that nurses working double shifts experience an alarming reversal of this pattern: their midnight cortisol levels are dramatically elevated, signaling an ongoing state of physiological stress when the body should be recovering.
In a study of rotating-shift nurses, salivary cortisol measured at midnight was approximately twice as high in nurses after double shifts compared with single-shift colleagues. The results suggest extended work schedules do more than increase fatigue—they disrupt the circadian rhythm and keep the body in a heightened stress state during hours normally reserved for recovery.
Key Facts
- Normal cortisol rhythm: Cortisol typically peaks in the early morning to support alertness and energy, then declines across the day and reaches a low point around midnight.
- Midnight spike with double shifts: Nurses working double shifts had salivary cortisol levels at midnight about two times higher than nurses working single shifts.
- Circadian disruption: The elevated midnight cortisol indicates a disruption of the circadian rhythm and reflects sustained physiological strain rather than normal short-term alertness.
- Study participants: The research monitored 52 female nurses working rotating shifts, comparing cortisol responses across single and double-shift schedules.
- Health implications: Chronic misalignment of cortisol patterns is linked to long-term risks such as burnout, cardiovascular strain, impaired immune function, and other stress-related health problems.
Source: Wiley
Cortisol helps the body wake up and meet daytime demands, with levels usually highest in the early morning and tapering off as the day progresses. This daily rhythm supports sleep, tissue repair, and cardiovascular recovery at night. The new analysis published in Nursing Open demonstrates that extended work hours can alter this rhythm: salivary cortisol at midnight was markedly higher in nurses after double shifts compared to single shifts.
The study enrolled 52 female nurses on rotating schedules. Saliva samples were collected at three time points—morning (07:30–08:30), afternoon (15:30–16:30), and around midnight (23:00–24:00)—for both single and double-shift conditions. The findings reveal not only higher overall cortisol among double-shift workers but also a significant interaction between time of day and shift type, indicating the pattern of cortisol secretion changes with extended hours.
Corresponding author Fadime Ulupınar, RN, MSc, of Erzurum Technical University in Turkey, explains that the evidence points to extended shifts causing circadian pattern alterations and increased physiological strain in nurses who work prolonged hours.
Key Questions Answered:
A: Cortisol elevation can temporarily boost alertness, but it represents an emergency-style stress response. Nighttime is when blood pressure drops and tissues repair; if cortisol remains high at midnight, the body misses this recovery window. Over time this persistent “wear and tear” increases the risk of physical and mental health problems.
A: The study detected elevated cortisol in nurses actively working double shifts, indicating that the physiological strain can be an immediate effect of prolonged schedules. Repeated exposure to these spikes may lead to more lasting circadian misalignment and chronic health consequences even on days off.
A: Both rotating and double shifts place stress on the internal clock, but they affect it differently. Rotating shifts disrupt the timing of the circadian system, while double shifts extend the duration of stress exposure. A double shift effectively forces the body to remain in a high-cortisol state for much longer, producing more acute physiological strain.
Editorial Notes:
- Edited by a Neuroscience News editor.
- Journal article reviewed in full.
- Additional context provided by editorial staff.
About this stress and circadian rhythm research news
Author: Sara Henning-Stout
Source: Wiley
Contact: Sara Henning-Stout, Wiley
Image: Image credited to Neuroscience News
Original Research: Open access. “The Effect of Single and Double Shift Works on Salivary Cortisol Levels in Nurses” by Fadime Ulupınar, Sibel Meler, and Engin Şebin. Nursing Open. DOI: 10.1002/nop2.70495
Abstract
The Effect of Single and Double Shift Works on Salivary Cortisol Levels in Nurses
Aim
This study aimed to clarify how single versus double-shift work schedules affect salivary cortisol concentrations in nurses, with a focus on circadian pattern changes and physiological strain associated with extended hours.
Design
Researchers used a comparative descriptive design with repeated measures to track cortisol changes over time and across shift types, enabling a direct comparison between single and double-shift effects within the same participants.
Methods
Fifty-two female nurses working rotating shifts participated. Saliva samples were collected at three time windows—morning (07:30–08:30), afternoon (15:30–16:30), and midnight (23:00–24:00)—for both single and double shifts. A repeated-measures two-way ANOVA examined interactions between time of day and shift type.
Results
Analyses showed significant main effects for both time and shift type. Cortisol was highest in the morning and lowest at midnight under normal conditions, but double-shift workers had higher mean cortisol overall. At midnight, cortisol levels in double-shift nurses were nearly double those of single-shift nurses, and a significant interaction between time and shift type confirmed that extended work hours altered the normal daily cortisol profile.
Conclusion
The clear impact of double shifts on cortisol regulation highlights the need for healthcare administrators and policymakers to weigh operational demands against nurses’ physiological well-being and patient safety. Strategies to limit prolonged consecutive work hours or to provide compensatory recovery could reduce chronic stress-related risks.
Patient or Public Contribution
No patient or public contribution to this study.