Lawson, ChristinaWhelan, ElizabethHibert, Eileen N. LividotiSpiegelman, DonnaSchernhammer, EvaRich-Edwards, Janet2019-09-212011Lawson, Christina C., Elizabeth A. Whelan, Eileen N. Lividoti Hibert, Donna Spiegelman, Eva S. Schernhammer, and Janet W. Rich-Edwards. 2011. “Rotating Shift Work and Menstrual Cycle Characteristics.” Epidemiology 22 (3): 305–12. https://doi.org/10.1097/ede.0b013e3182130016.1044-39831531-5487http://nrs.harvard.edu/urn-3:HUL.InstRepos:41384819Background: 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.en-USJournal Article2019-09-2110.1097/EDE.0b013e3182130016