Night shift work in nurses was associated with significantly lower urinary cortisol (p=0.0012) and 6-sulfatoxymelatonin (p<0.0001) excretion compared to day shift work, with no phase adaptation.
Observational (n=19)
Does night shift work disrupt the circadian periodicity of urinary cortisol and melatonin in healthy female nurses compared to day shift work?
Night shift work in nurses is associated with disrupted circadian rhythms, characterized by lower excretion of cortisol and melatonin, which may have long-term health implications.
p-value: p=0.0012
Objective: To study the degree of disruption of the circadian periodicity of urinary cortisol and melatonin in nurses working on either day or night shifts. Methods: Nineteen young adult healthy women holding only one job participated in this study. The night workers (n=12) worked 12h night shift (19:00-07:00) followed by 36h off, having one extra off day twice a month, resulting in three consecutive free nights. Day workers (n=7) worked 6 days a week 6 hours per shift, 6 worked during the afternoon shift (13:00 to 19:00) and one worked at morning shift (07:00-13:00), all having one free day per week. Participants wore an actigraph to monitor activity-rest times and filled out a daily log to register perceived sleep quality. Nurses were classified as more tolerant (n=8) and less tolerant (n=4) to night work, being considered less tolerant ones those who exhibited at least two of these parameters: fatigue, sleep disturbances, sleepiness, insomnia, minor psychic disorders, and reduced availability of free time off work. Urine was collected during waking hours in two different times of four consecutive days to measure 6-sulphatoxymelatonin (6SOHMel) and cortisol. The data were analyzed by the single cosinor for each subject during each study period and for the days on night shift and the days off. Each group during each of the examined time spans was analyzed by ANOVA and cosinor. Results and Discussion: Day workers and night workers on working days and on days off showed a circadian rhythm for cortisol excretion (acrophase between 12:00 and 13:30). ANOVA indicated lower cortisol excretion in the night workers on the day of work (day workers vs. night workers at work, p=0.0012) with recovery on the days of rest (night workers at work vs. off work, p=0.04l2). The sum of all cortisol values was lower in the less tolerant night workers than more tolerant ones (p=0.0473). Examining separately days on night work and days off, the lower values appear to be due to lower values on work days, although in the separate groups statistical significance was only marginal (p=0.054). In the day workers, a circadian variation for 6SOHMel excretion was confirmed by ANOVA, but not by cosinor (p=0.101) with an acrophase around 08:16. The night workers showed a circadian rhythm validated by cosinor on nights workers (p=0.001) and on days of rest (p=0.002) with acrophases at a 08:04 and 08:08 respectively, corresponding to the morning urine collection. The circadian mean was significantly lower than the day workers in the days of work (p<0.0001) and remained so in the days off work (p<0.0001). The sum of all 6SOHMel values was lower in the less tolerant workers than more tolerant ones (p=0.0426). Conclusion: Night workers with alternating days off, have no phase adaptation of cortisol or melatonin to the night shift. Suppression of melatonin in shiftworkers is thought to be one of the mechanisms leading to an increased cancer incidence. Subjects with lower tolerance of shift work show lower cortisol and 6SOHMel excretion, but this needs to be better evaluated. Support: CAPES, CNPq, the Health Partners Research Foundation, Grant # 99-130, Fogarty International Center, Mount Sinai School of Medicine, NY, USA. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil
Borges et al. (Thu,) conducted a observational in Shift work (n=19). Night shift work vs. Day shift work was evaluated on Urinary cortisol and 6-sulfatoxymelatonin excretion (p=0.0012). Night shift work in nurses was associated with significantly lower urinary cortisol (p=0.0012) and 6-sulfatoxymelatonin (p<0.0001) excretion compared to day shift work, with no phase adaptation.