Night Shift Work and Hormone Levels in Women

Feb 9, 2012Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology

How working night shifts is linked to hormone levels in women

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Abstract

6-Sulfatoxymelatonin levels were 62% lower in night shift-working women during daytime sleep compared to day shift-working women during nighttime sleep.

Night shift workers exhibited higher levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by 58% and 62%, respectively, during daytime sleep.
Nighttime sleep on off-nights for night shift workers was associated with 42% lower 6-sulfatoxymelatonin levels compared to day shift workers.
During night work, 6-sulfatoxymelatonin levels were approximately 69% lower in night shift workers compared to day shift workers at night.
No significant differences in estrone conjugate (E1C) levels were found between night and day shift workers.
Overall, night shift work is linked to reduced melatonin levels and increased reproductive hormone levels.

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BACKGROUND: Night shift work may disrupt the normal nocturnal rise in melatonin, resulting in increased breast cancer risk, possibly through increased reproductive hormone levels. We investigated whether night shift work is associated with decreased levels of urinary 6-sulfatoxymelatonin, the primary metabolite of melatonin, and increased urinary reproductive hormone levels.

METHODS: Participants were 172 night shift and 151 day shift-working nurses, aged 20-49 years, with regular menstrual cycles. Urine samples were collected throughout work and sleep periods and assayed for 6-sulfatoxymelatonin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrone conjugate (E1C).

RESULTS: 6-Sulfatoxymelatonin levels were 62% lower and FSH and LH were 62% and 58% higher, respectively, in night shift-working women during daytime sleep than in day shift-working women during nighttime sleep (P ≤ 0.0001). Nighttime sleep on off-nights was associated with 42% lower 6-sulfatoxymelatonin levels among the night shift workers, relative to the day shift workers (P < 0.0001); no significant differences in LH or FSH were observed. 6-Sulfatoxymelatonin levels during night work were approximately 69% lower and FSH and LH were 35% and 38% higher, compared with day shift workers during nighttime sleep. No differences in E1C levels between night and day shift workers were observed. Within night shift workers, 6-sulfatoxymelatonin levels were lower and reproductive hormone levels were higher during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.05).

CONCLUSIONS: These results indicate that night shift workers have substantially reduced 6-sulfatoxymelatonin levels during night work and daytime sleep and that levels remain low even when a night shift worker sleeps at night.

IMPACT: Shift work could be an important risk factor for many other cancers in addition to breast cancer.

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Night Shift Work and Hormone Levels in Women

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