title: Menstrual and reproductive factors and gastric cancer risk in a large prospective study of women.
abstract: BACKGROUND
  Gastric cancer incidence rates are consistently lower in women than men in both high and low-risk regions worldwide. Sex hormones, such as progesterone and estrogen, may protect women against gastric cancer.
  
  
  OBJECTIVE
  To investigate the association of menstrual and reproductive factors and gastric cancer risk.
  
  
  METHODS
  These associations were prospectively investigated in 73 442 Shanghai women. After 419 260 person-years of follow-up, 154 women were diagnosed with gastric cancer. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazards models adjusted for age, body mass index, education, income, and cigarette use.
  
  
  RESULTS
  No associations were observed between gastric cancer risk and age of menarche, number of children, breast feeding, or oral contraceptive use. In contrast, associations were observed with age of menopause (HR 0.80 per five-year increase in menopausal age, 95% CI 0.66-0.97), years of fertility (participants with less than 30 years of fertility were at increased risk compared with those with 30-36 years of fertility, HR 1.90, 95% CI 1.25-2.90), years since menopause (HR 1.26 per five years, 95% CI 1.03-1.53), and intrauterine device use (HR for users 1.61, 95% CI 1.08-2.39).
  
  
  CONCLUSIONS
  These results support the hypothesis that female hormones play a protective role in gastric cancer risk.
authors.affiliation: Cancer Prevention Fellowship Program, Division of Cancer Prevention, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA. freedmanne@mail.nih.gov
authors.forename: Neal D
authors.initials: ND
authors.lastname: Freedman
authors.forename: Wong-Ho
authors.initials: WH
authors.lastname: Chow
authors.forename: Yu-Tang
authors.initials: YT
authors.lastname: Gao
authors.forename: Xiao-Ou
authors.initials: XO
authors.lastname: Shu
authors.forename: Bu-Tian
authors.initials: BT
authors.lastname: Ji
authors.forename: Gong
authors.initials: G
authors.lastname: Yang
authors.forename: Jay H
authors.initials: JH
authors.lastname: Lubin
authors.forename: Hong-Lan
authors.initials: HL
authors.lastname: Li
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Rothman
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.forename: Christian C
authors.initials: CC
authors.lastname: Abnet
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D002681:China / Q000453:epidemiology; D004522:Educational Status; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008572:Menarche; D008593:Menopause; D008598:Menstruation; D008875:Middle Aged; D017584:Reproductive History; D012959:Socioeconomic Factors; D013274:Stomach Neoplasms / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control; D013997:Time Factors