title: [Thelarche and nutritional status: an epidemiological study of two ethnic groups].
abstract: BACKGROUND
  Improvements in environmental conditions may result in an earlier onset of thelarche. However, its onset is not homogeneous among different population groups.
  
  
  OBJECTIVE
  To assess the relationship between nutritional status, ethnicity and age of thelarche.
  
  
  METHODS
  Cross-sectional study of girls in second through sixth grade, attending 165 schools located in Chile's Araucania region. Of these, 231 girls who presented thelarche (breast button) were selected. The girls' surnames were used to identify their ethnicity: indigenous had three or four last names of Mapuche indigenous origin (n =113), while non-indigenous were those who only had Chilean-Spanish last names (n =118). Weight, height, waist circumference and skinfold thicknesses were measured and socio-economic background information was collected through a home interview.
  
  
  RESULTS
  The median age of thelarche was 10 years and 4 months, regardless of ethnic group. Multivariant models showed that an increase of one z score unit of body mass index (BMI) decreased the median age of thelarche by 5.6 months (CI: -7.24 to -3.90), controlling for the effect of different covariables. A decrease in one z score of height retards the median age of thelarche by 5.5 months (CI: 4.02 to 6.98). Ethnicity did not influence the age of thelarche.
  
  
  CONCLUSIONS
  The age of thelarche found by us is similar to that reported in international studies, it comes earlier as weight increases, is delayed as height decreases and is not related to ethnicity.
authors.affiliation: Departamento de Nutrición, Facultad de Medicina, Universidad de Chile, Santiago de Chile. pbustos@med.uchile.cl
authors.forename: Patricia
authors.initials: P
authors.lastname: Bustos
authors.forename: Hugo
authors.initials: H
authors.lastname: Amigo
authors.forename: Santiago
authors.initials: S
authors.lastname: Muzzo
authors.forename: Ximena
authors.initials: X
authors.lastname: Ossa
mesh_terms: D017668:Age of Onset; D015992:Body Mass Index; D001940:Breast / Q000254:growth & development*; D002648:Child; D002677:Chile / Q000208:ethnology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007199:Indians, South American / Q000208:ethnology / Q000706:statistics & numerical data; D015999:Multivariate Analysis; D009752:Nutritional Status / Q000208:ethnology* / Q000502:physiology; D011629:Puberty, Precocious / Q000208:ethnology* / Q000473:pathology