title: Reproductive and menstrual factors and colorectal cancer incidence in the Women's Health Initiative Observational Study.
abstract: Reproductive and menstrual factors have been evaluated as surrogates for long-term hormonal exposures in several prospective studies of colorectal cancer, yet findings have been conflicting.
  
  
  
  The relation of reproductive and menstrual factors (self-reported via a reproductive history questionnaire) with incident colorectal cancer was investigated among women enrolled in the Women's Health Initiative Observational Study (WHI-OS), a longitudinal cohort of 93 676 postmenopausal women (aged 50-79 years at enrolment) in which 1149 incident cases of colorectal cancer occurred over a median follow-up of 11.9 years. Multivariable Cox proportional hazards models that included established colorectal cancer risk factors were constructed to examine the association of colorectal cancer incidence with reproductive and menstrual factors.
  
  
  
  Having had two children (vs nulliparous: hazard ratio (HR)=0.80, 95% confidence interval (CI): 0.64-0.99) was inversely associated with colorectal cancer risk. Compared with never users, ever use of oral contraceptives was associated with lower colorectal cancer risk (HR=0.74, 95% CI: 0.63-0.86); however, no relationship was observed for duration of oral contraceptives use (4 years vs 1 year: HR=0.94, 95% CI: 0.67-1.32). None of the remaining reproductive and menstrual factors was associated with colorectal cancer incidence.
  
  
  
  Parity and prior use of oral contraceptives were associated with lower colorectal cancer risk in this cohort of postmenopausal women.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College, London, UK.|Section of Nutrition and Metabolism, International Agency for Research on Cancer, Lyon, France.
authors.forename: Neil
authors.initials: N
authors.lastname: Murphy
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Linzhi
authors.initials: L
authors.lastname: Xu
authors.affiliation: Department of Oncology, Montefiore Medical Center, Bronx, New York, NY, USA.
authors.forename: Alice
authors.initials: A
authors.lastname: Zervoudakis
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Xue
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Kabat
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Rohan
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Wassertheil-Smoller
authors.affiliation: Department of Obstetrics and Gynecology, University of Miami, Miami, FL, USA.
authors.forename: Mary Jo
authors.initials: MJ
authors.lastname: O'Sullivan
authors.affiliation: Mel and Enid Zuckerman College of Public Health, University of Arizona Canyon Ranch Center for Prevention & Health Promotion, Tucson, AZ, USA.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Thomson
authors.affiliation: Department of Preventive Medicine, Stony Brook University, Stony Brook, NY, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Messina
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY, USA.
authors.forename: Howard D
authors.initials: HD
authors.lastname: Strickler
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College, London, UK.|Section of Nutrition and Metabolism, International Agency for Research on Cancer, Lyon, France.
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Gunter
mesh_terms: D000367:Age Factors; D000368:Aged; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D008597:Menstrual Cycle / Q000502:physiology*; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*; D017584:Reproductive History; D012307:Risk Factors; D016387:Women's Health