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Updated: May 25, 2026
06:39
Through-the-Wall Blood Sampling Method to Minimize Sleep Disruption in Clinical Settings
Published on: June 13, 2025
Night shift work and hormone levels in women
Scott Davis1, Dana K Mirick, Chu Chen
1Program In Epidemiology, Division of Public HealthSciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA.
Summary
Night shift work significantly lowers melatonin and raises reproductive hormones, potentially increasing cancer risk. These hormonal changes persist even during off-duty sleep for night shift nurses.
Area of Science:
- Endocrinology
- Occupational Health
- Cancer Epidemiology
Background:
- Night shift work may disrupt melatonin production, a hormone linked to circadian rhythms.
- Disrupted melatonin may increase breast cancer risk by altering reproductive hormone levels.
Purpose of the Study:
- To investigate the association between night shift work and urinary melatonin metabolite (6-sulfatoxymelatonin) levels.
- To examine the relationship between night shift work and urinary reproductive hormone levels (LH, FSH, E1C).
Main Methods:
- Compared 172 night shift nurses with 151 day shift nurses (aged 20-49).
- Collected and analyzed urine samples for 6-sulfatoxymelatonin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrone conjugate (E1C).
- Assessed hormone levels during work and sleep periods.
Main Results:
- Night shift workers showed 62% lower 6-sulfatoxymelatonin and higher FSH (62%) and LH (58%) during daytime sleep compared to day workers during nighttime sleep.
- Reduced 6-sulfatoxymelatonin levels (42%) were observed during off-night sleep in night shift workers.
- During night work, 6-sulfatoxymelatonin was 69% lower, while FSH and LH were higher (35-38%) compared to day workers' nighttime sleep.
Conclusions:
- Night shift work is associated with significantly reduced 6-sulfatoxymelatonin levels during work and sleep.
- Elevated reproductive hormone levels correlate with night shift work and reduced melatonin.
- Shift work may be a risk factor for various cancers beyond breast cancer.
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