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Epidemiology:
doi: 10.1097/EDE.0b013e3182130016
Reproduction: Original Article

Rotating Shift Work and Menstrual Cycle Characteristics

Lawson, Christina C.a; Whelan, Elizabeth A.a; Lividoti Hibert, Eileen N.b; Spiegelman, Donnac,d; Schernhammer, Eva S.b; Rich-Edwards, Janet W.c,e

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Abstract

Background: Shift workers who experience sleep disturbances and exposure to light at night could be at increased risk for alterations in physiologic functions that are circadian in nature.

Methods: We investigated rotating shift work and menstrual cycle patterns in the Nurses' Health Study II using cross-sectional data collected in 1993 from 71,077 nurses aged 28–45 years who were having menstrual periods and were not using oral contraceptives. Log-binomial regression was used to estimate relative risks (RRs) and 95% confidence intervals (CIs).

Results: Eight percent of participants reported working rotating night shifts for 1–9 months, 4% for 10–19 months, and 7% for 20+ months during the previous 2 years. Irregular cycles (>7 days variability) were reported by 10% of participants. Seventy percent of women reported menstrual cycles of 26–31 days, 1% less than 21 days, 16% 21–25 days, 11% 32–39 days, and 1% 40+ days. Women with 20+ months of rotating shift work were more likely to have irregular cycles (adjusted RR = 1.23 [CI = 1.14–1.33]); they were also more likely to have cycle length <21 days (1.27 [0.99–1.62]) or 40+ days (1.49 [1.19–1.87]) (both compared with 26–31 days). For irregular patterns and for 40+ day cycles, there was evidence of a dose response with increasing months of rotating shift work. Moderately short (21–25 days) or long (32–39 days) cycle lengths were not associated with rotating shift work.

Conclusions: Shift work was modestly associated with menstrual function, with possible implications for fertility and other cycle-related aspects of women's health.

© 2011 Lippincott Williams & Wilkins, Inc.

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