title: Oral contraceptive use and colorectal cancer in the Nurses' Health Study I and II.
abstract: BACKGROUND
  It remains unclear if oral contraceptive (OC) use is associated with the incidence of colorectal cancer. Few studies have examined this association by duration of OC use, time since last OC use, and different cancer subsites.
  
  
  METHODS
  Among 88,691 participants of the Nurses' Health Study I (NHSI) and 93,080 participants of the Nurses' Health Study II (NHSII), we assessed OC use every 2 years between 1976 and 2010 and categorized it as ever use, duration of use, and time since last use. We included incident colorectal cancer cases through 2010 (NHSI: age at diagnosis = 36-88, N = 1,764; NHSII: age at diagnosis = 33-64, N = 206). Multivariable hazard ratios and 95% confidence intervals were estimated using Cox proportional hazards regression models.
  
  
  RESULTS
  Ever OC use was not associated with colorectal cancer in NHSI [1.01 (0.91, 1.12)] nor NHSII [1.03 (0.69, 1.53)]. In NHSII, when compared with never-users, longer durations (5+ years) of OC use were inversely associated with the risk of colon cancers (Ptrend = 0.02) but the number of endpoints was limited. No other colorectal cancer subsites were associated with OC durations or times since last OC use in either cohort.
  
  
  CONCLUSIONS
  In two large prospective cohorts, we found little evidence that OC use may be protective for colorectal cancer, except potentially with longer durations of use among younger women.
  
  
  CONCLUSIONS
  Our results do not support the previous initial studies that reported an inverse association of recent OC use with colorectal cancer but instead support newer, larger studies demonstrating no such association.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Division of Adolescent and Young Adult Medicine, Boston Children's Hospital, Boston, Massachusetts. Department of Pediatrics, Harvard Medical School, Boston, Massachusetts. bcharlton@mail.harvard.edu.
authors.forename: Brittany M
authors.initials: BM
authors.lastname: Charlton
authors.affiliation: Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Kana
authors.initials: K
authors.lastname: Wu
authors.affiliation: Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Xuehong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Edward L
authors.initials: EL
authors.lastname: Giovannucci
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fuchs
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts. Division of Reproductive Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Stacey A
authors.initials: SA
authors.lastname: Missmer
authors.affiliation: Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Bernard
authors.initials: B
authors.lastname: Rosner
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts. Division of Biostatistics and Epidemiology, School of Public Health and Health Sciences, University of Massachusetts, Boston, Massachusetts.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hankinson
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts. Obstetrics and Gynecology Epidemiology Center, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Karin B
authors.initials: KB
authors.lastname: Michels
mesh_terms: D000328:Adult; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D003276:Contraceptives, Oral; D005260:Female; D006801:Humans; D008875:Middle Aged; D009726:Nurses; D011446:Prospective Studies
chemical_list: D003276:Contraceptives, Oral