title: Childbearing, breastfeeding, other reproductive factors and the subsequent risk of hospitalization for gallbladder disease.
abstract: BACKGROUND
  While parous women are known to be at an increased risk of gallbladder disease, little is known about the effects of other reproductive factors such as breastfeeding, age at menarche and age at menopause.
  
  
  METHODS
  The Million Women Study is a prospective cohort study of 1.3 million middle-aged women in England and Scotland recruited from 1996 to 2001. Participants were followed-up by record-linkage for a mean of 6.1 years for admissions to hospital. The adjusted relative risk of hospital admission for cholelithiasis, cholecystitis or cholecystectomy according to parity, breastfeeding, age at menarche and age at menopause was examined.
  
  
  RESULTS
  During follow-up of 1 289 029 eligible women, 25 111 were admitted to hospital for gallbladder disease, of whom 21 735 (87%) had a cholecystectomy. The hospital admission rate over 5 years for gallbladder disease was 1.6/100 women and for cholecystectomy was 1.4/100 women. The adjusted relative risk of gallbladder disease increased with increasing parity by 8% (95% CI 7-9%, P < 0.0001) for each birth. Among women of a given parity, breastfeeding reduced the risk of gallbladder disease, the relative risk decreasing by 7% (95% CI 5-10%, P < 0.0001) per year of breastfeeding. Women's age of menarche and age at menopause did not alter the risk of gallbladder disease (P = 0.4 and P = 0.3, respectively for linear trend).
  
  
  CONCLUSIONS
  Hospitalization for gallbladder disease is common in middle-aged women. The risk increases the more children a woman has had, but decreases the longer she breastfeeds. The increased risk of gallbladder disease associated with having children can be offset by breastfeeding.
authors.affiliation: Cancer Epidemiology Unit, University of Oxford, Richard Doll Building, Roosevelt Drive, Oxford OX3 7LF, UK. bette.liu@ceu.ox.ac.uk
authors.forename: Bette
authors.initials: B
authors.lastname: Liu
authors.forename: Valerie
authors.initials: V
authors.lastname: Beral
authors.forename: Angela
authors.initials: A
authors.lastname: Balkwill
mesh_terms: D000367:Age Factors; D001942:Breast Feeding / Q000706:statistics & numerical data*; D004739:England / Q000453:epidemiology; D005260:Female; D005705:Gallbladder Diseases / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008572:Menarche; D008593:Menopause; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D011446:Prospective Studies; D017584:Reproductive History; D018570:Risk Assessment / Q000379:methods; D012606:Scotland / Q000453:epidemiology