title: Breastfeeding practice, oral contraceptive use and risk of rheumatoid arthritis among Chinese women: the Guangzhou Biobank Cohort Study.
abstract: OBJECTIVE
  Hormonal and reproductive factors are implicated in the aetiology of RA, but results of previous studies have been mixed. The aim of this cross-sectional study was to assess the relationships between RA, use of oral contraceptives (OCs) and history of breastfeeding in a population of older women from South China.
  
  
  METHODS
  We used baseline data from 7349 women ≥ 50 years of age in the Guangzhou Biobank Cohort. Questionnaires were used to obtain socio-demographic, lifestyle and obstetric history data, including parity, OC use and breastfeeding practices. The main outcome was RA. Women were asked about history of RA and were examined to assess joint swelling. RF levels were measured. The presence of RA was defined in two ways: (i) as reporting physician-diagnosed RA or pain and swelling in at least three joints (including the wrist), and (ii) also having at least one of the following: positive RF, morning stiffness or objective swelling of the small joints of the hands.
  
  
  RESULTS
  Compared with those who had never breastfed, breastfeeding was associated with half the risk of RA. The risk was lower with increasing duration of breastfeeding [adjusted odds ratio (OR) 0.54 (95% CI 0.29, 1.01) for breastfeeding at least 36 months; P for trend = 0.04]. OC use had no relationship with RA.
  
  
  CONCLUSIONS
  Breastfeeding (especially longer duration) but not OC use is associated with a lower risk of RA. This has potentially important implications for future RA disease burden, given the declining rates of breastfeeding and the one-child policy in China. Further research is needed to explain the biological mechanism.
authors.affiliation: Department of Rheumatology, University Hospital Birmingham, Mindelsohn Way, Edgbaston, Birmingham B15 2WB, UK. elizabeth.rankin@uhb.nhs.uk.
authors.forename: Peymane
authors.initials: P
authors.lastname: Adab
authors.forename: Chao Qiang
authors.initials: CQ
authors.lastname: Jiang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Rankin
authors.forename: Yee Wah
authors.initials: YW
authors.lastname: Tsang
authors.forename: Tai Hing
authors.initials: TH
authors.lastname: Lam
authors.forename: Johanna
authors.initials: J
authors.lastname: Barlow
authors.forename: G Neil
authors.initials: GN
authors.lastname: Thomas
authors.forename: Wei Sen
authors.initials: WS
authors.lastname: Zhang
authors.forename: Kar Keung
authors.initials: KK
authors.lastname: Cheng
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000453:epidemiology* / Q000208:ethnology*; D044466:Asian People / Q000208:ethnology*; D001942:Breast Feeding; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D015995:Prevalence; D012307:Risk Factors; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires
chemical_list: D003276:Contraceptives, Oral
keywords: Chinese; breastfeeding; epidemiology; oral contraceptives; rheumatoid arthritis; risk factors