title: Early life factors and adult-onset rheumatoid arthritis.
abstract: OBJECTIVE
  Early life factors have been associated with risk of developing autoimmune disease in adulthood. We investigated the association of preterm birth and being breastfed with the incidence of rheumatoid arthritis (RA) in 2 large prospective cohorts.
  
  
  METHODS
  We studied participants from the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHSII) who provided information on perinatal factors. The NHS (n = 121,701) and NHSII (n = 116,608) are large prospective cohorts of women followed since 1976 and 1989, respectively. Incident RA was confirmed using the American College of Rheumatology criteria and a medical record review. Cox models were used to estimate the hazard ratio of RA associated with being born preterm and being breastfed and its duration, adjusting for potential confounders. Random effects metaanalytic methods were used to compute combined estimates from the 2 cohorts.
  
  
  RESULTS
  We found no statistically significant association between preterm birth and incident RA [relative risk (RR) = 1.1, 95% CI 0.8, 1.5]. Being breastfed was not associated with increased incidence of RA (RR = 1.0, 95% CI 0.7, 1.4), regardless of the duration of breastfeeding.
  
  
  CONCLUSIONS
  In these cohorts of women, neither being preterm birth nor being breastfed was associated with the onset of RA.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA. julia.simard@post.harvard.edu
authors.forename: Julia F
authors.initials: JF
authors.lastname: Simard
authors.forename: Karen H
authors.initials: KH
authors.lastname: Costenbader
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Hernán
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Liang
authors.forename: Murray A
authors.initials: MA
authors.lastname: Mittleman
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Karlson
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000209:etiology* / Q000503:physiopathology; D001724:Birth Weight; D001942:Breast Feeding; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D047928:Premature Birth; D016016:Proportional Hazards Models; D012307:Risk Factors