Rotating shift work and menstrual cycle characteristics.
Lawson-CC; Whelan-EA; Lividoti Hibert-EN; Spiegelman-D; Schernhammer-ES; Rich-Edwards-JW
Epidemiology 2011 May; 22(3):305-312
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.
Sleep-disorders; Physiological-stress; Physiological-function; Physiological-factors; Physiological-effects; Women; Shift-work; Shift-workers; Age-groups
Christina C. Lawson, NIOSH, CDC, 4676 Columbia Parkway, R-15, Cincinnati, OH 45226
Healthcare and Social Assistance
Brigham and Women's Hospital, Inc., Boston, Massachusetts