ORIGINAL ARTICLE
Night work and differential effects on diurnal rhythms of cortisol, melatonin, and testosterone among permanent night-working men
1
The National Research Centre for the Working Environment, Copenhagen, Denmark.
2
Department of Public Health, Section of Social Medicine, University of Copenhagen, Centre for Health and Society, Copenhagen, Denmark.
3
Appleton Institute for Behavioural Science, Central Queensland University, Wayville SA, Australia
4
Department of Public Health, Erasmus University Medical Center, Rotterdam, The Netherlands
5
Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
Submission date: 2026-03-11
Final revision date: 2026-06-03
Acceptance date: 2026-09-09
Online publication date: 2026-10-13
Corresponding author
Anne Helene Garde
The National Research Centre for the Working Environment, Lersø Parkallé 105, 2100 Copenhagen, Denmark.
The National Research Centre for the Working Environment, Lersø Parkallé 105, 2100 Copenhagen, Denmark.
KEYWORDS
night workdiurnal rhythmcortisolmelatonintestosteronecircadian rhythmendocrine systemnight shift worknight workerpermanent night work
ABSTRACT
Objective(s):
Night work-induced circadian misalignment is associated with an increased risk of adverse health effects. It has been suggested that permanent night workers can entrain to being awake at night and therefore do not experience substantial circadian disruption in relation to night work. The aim of this study was to investigate the effects of night work on diurnal rhythms of cortisol, melatonin, and testosterone among permanent night workers.
Methods:
Twenty-three men with permanent night work participated in this observational field study. They collected saliva every 4 hours over a 24-hour period for assessment of diurnal rhythms (mesor, amplitude and acrophase) on three days: the 2nd and 4th consecutive night shifts, and a day off. Within-person regression analyses with repeated measures adjusted for age were used to evaluate differences between the 2nd and 4th night shifts and between night shifts taken together versus days off.
Results:
There were no statistically significant differences between diurnal rhythms on the 2nd and 4th consecutive night shifts. We observed differences in levels (mesor and amplitude) of cortisol and melatonin on night shifts compared to days off with the highest levels during work days. The timing (acrophase) of testosterone, but not cortisol and melatonin, differed between night shifts and days off. Thus, observed differences between the various hormonal diurnal rhythms to night work indicate internal desynchronization.
Conclusion(s):
Studies of how diurnal rhythms of multiple biological systems are affected by night work and the link to health effects are warranted to further elucidate the mechanisms linking night work to adverse health effects.
Night work-induced circadian misalignment is associated with an increased risk of adverse health effects. It has been suggested that permanent night workers can entrain to being awake at night and therefore do not experience substantial circadian disruption in relation to night work. The aim of this study was to investigate the effects of night work on diurnal rhythms of cortisol, melatonin, and testosterone among permanent night workers.
Methods:
Twenty-three men with permanent night work participated in this observational field study. They collected saliva every 4 hours over a 24-hour period for assessment of diurnal rhythms (mesor, amplitude and acrophase) on three days: the 2nd and 4th consecutive night shifts, and a day off. Within-person regression analyses with repeated measures adjusted for age were used to evaluate differences between the 2nd and 4th night shifts and between night shifts taken together versus days off.
Results:
There were no statistically significant differences between diurnal rhythms on the 2nd and 4th consecutive night shifts. We observed differences in levels (mesor and amplitude) of cortisol and melatonin on night shifts compared to days off with the highest levels during work days. The timing (acrophase) of testosterone, but not cortisol and melatonin, differed between night shifts and days off. Thus, observed differences between the various hormonal diurnal rhythms to night work indicate internal desynchronization.
Conclusion(s):
Studies of how diurnal rhythms of multiple biological systems are affected by night work and the link to health effects are warranted to further elucidate the mechanisms linking night work to adverse health effects.
ACKNOWLEDGEMENTS
We would like to thank all the participants. We would also like to thank Jonas Gjerluf Stentebjerg Christensen, Marie Aarrebo Jensen, Anne Abildtrup, Ulla Tegner and Simon Pelle Jensen for their skilled contribution to the statistical analyses, data collection and analyses of cortisol, melatonin and testosterone. Vivi Schlünssen is acknowledged for her role as medical supervisor and fruitful discussions in the data collection.
FUNDING
The study was funded by The Danish Working Environment Research Fund (grant 10-2011-09 and 23-2017-09), the Danish Cardiovascular Academy (Novo Nordisk Foundation grant NNF17SA0031406), and the Danish Heart Foundation.
CONFLICT OF INTEREST
None
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