title: Rotating shift work and menstrual cycle characteristics.
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.
authors.affiliation: National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, OH 45226, USA. clawson@cdc.gov
authors.forename: Christina C
authors.initials: CC
authors.lastname: Lawson
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Whelan
authors.forename: Eileen N
authors.initials: EN
authors.lastname: Lividoti Hibert
authors.forename: Donna
authors.initials: D
authors.lastname: Spiegelman
authors.forename: Eva S
authors.initials: ES
authors.lastname: Schernhammer
authors.forename: Janet W
authors.initials: JW
authors.lastname: Rich-Edwards
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000367:Age Factors; D021081:Chronobiology Disorders / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D015994:Incidence; D016014:Linear Models; D008597:Menstrual Cycle / Q000502:physiology*; D008599:Menstruation Disturbances / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology; D008875:Middle Aged; D015999:Multivariate Analysis; D009726:Nurses / Q000706:statistics & numerical data*; D011379:Prognosis; D018570:Risk Assessment; D011795:Surveys and Questionnaires; D014940:Work Schedule Tolerance