title: Breast-feeding and mental and motor development at 51/2 years.
abstract: OBJECTIVE
  Breast-feeding is associated with better child development outcomes, but uncertainty remains primarily due to the close relationship between breast-feeding and socioeconomic status. This study assesses the issue in a low socioeconomic status sample where breast-feeding was close to universal.
  
  
  METHODS
  Seven hundred eighty-four Chilean children were followed longitudinally from infancy. All but four were initially breastfed, 40% nursed beyond 12 months, and infant growth was normal. Child development was assessed at 5(1/2) years by a cognitive, language, and motor test battery. The duration of breast-feeding as the sole milk source was analyzed as a continuous variable, adjusting for a comprehensive set of background factors.
  
  
  RESULTS
  The relationship between breast-feeding and most 5(1/2)-year developmental outcomes was nonlinear, with poorer outcome for periods of breast-feeding as the sole milk source for <2 months or >8 months--statistically significant for language, motor, and one comprehensive cognitive test, with a suggestive trend for IQ.
  
  
  CONCLUSIONS
  The observed nonlinear relationships showed that breast-feeding as the sole milk source for <2 months or >8 months, compared with 2-8 months, was associated with poorer development in this sample. The latter finding requires replication in other samples where long breast-feeding is common and socioeconomic status is relatively homogeneous.
authors.affiliation: Center for Human Growth and Development, University of Michigan, Ann Arbor, 48109, USA.
authors.forename: Katy M
authors.initials: KM
authors.lastname: Clark
authors.forename: Marcela
authors.initials: M
authors.lastname: Castillo
authors.forename: Agustin
authors.initials: A
authors.lastname: Calatroni
authors.forename: Tomas
authors.initials: T
authors.lastname: Walter
authors.forename: Marisol
authors.initials: M
authors.lastname: Cayazzo
authors.forename: Paulina
authors.initials: P
authors.lastname: Pino
authors.forename: Betsy
authors.initials: B
authors.lastname: Lozoff
mesh_terms: D000704:Analysis of Variance; D001942:Breast Feeding; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D003071:Cognition / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007361:Intelligence Tests; D008137:Longitudinal Studies; D008297:Male; D008606:Mental Processes / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D018570:Risk Assessment; D012959:Socioeconomic Factors; D013997:Time Factors