title: [Age at menarche and indigenous ancestry: a population study in Chile].
abstract: BACKGROUND
  The age at menarche may influence decisively health and disease in women. It also indicates the beginning of the reproductive period and, as a consequence, the possibility of biological continuity for the human species. Genetic and environmental determinants define the age of menarche and can explain differences found among different populations.
  
  
  OBJECTIVE
  To determine the age at menarche among adolescents with different levels of indigenous descent (parental indigenous surnames), considering the effect of socioeconomic and demographic factors.
  
  
  METHODS
  An observational study of historic cohorts of 8.624 girls from the Araucanía Region (central-southern Chile) was carried out. Data were collected by health professionals using a previously validated questionnaire. Occurrence of menarche was estimated through survival analysis and compared between groups (according to indigenous parental surnames) adjusted for parents' income and educational level and provenance (rural/urban).
  
  
  RESULTS
  Estimated median age of menarche was 151 months (95% Cl: 150-151). In female with four indigenous surnames, menarche occurred two months later than girls without indigenous surnames and with two indigenous surnames (p < 0,001). In girls whose parents had lowest level of schooling, the difference increased to eight months later (p < 0,005).
  
  
  CONCLUSIONS
  Age at menarche in the group with higher indigenous descent is later even if socio-economic conditions remain stable. Genetic factors might play an important role, however conditions of vulnerability can influence and further delay the onset of reproductive competency.
authors.affiliation: Departamento de Salud Pública, Facultad de Medicina, Universidad de La Frontera, Temuco, Chile. xossa@ufro.cl
authors.forename: Ximena
authors.initials: X
authors.lastname: Ossa
authors.forename: Patricia
authors.initials: P
authors.lastname: Bustos
authors.forename: Sergio
authors.initials: S
authors.lastname: Muñoz
authors.forename: Hugo
authors.initials: H
authors.lastname: Amigo
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D002677:Chile / Q000208:ethnology; D005260:Female; D006801:Humans; D007199:Indians, South American; D008572:Menarche / Q000208:ethnology* / Q000502:physiology; D008597:Menstrual Cycle / Q000208:ethnology* / Q000502:physiology; D008599:Menstruation Disturbances / Q000208:ethnology* / Q000503:physiopathology; D015995:Prevalence; D012424:Rural Population; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires