[Age at menarche and indigenous ancestry: a population study in Chile]

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.

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.

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).

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).

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.