Age of menarche and nutritional status of indigenous and non-indigenous adolescents in the Araucania Region of Chile

Background: Early onset of menarche has been linked to prevalence of obesity; however, this may differ for indigenous females. Objective: To analyse the relationship between age of menarche and nutritional status among indigenous and non-indigenous girls. Method: The design of this study was cross-sectional. Date of menarche was determined through interviews, and all responses were confirmed by the girls' mothers. A total of 8504 adolescents were screened for recent menarche. One hundred and thirty-one girls of Mapuche (indigenous) and 143 girls of Chilean-Spanish background were identified and evaluated by anthropometric measurements. Results: Median age of menarche was 150 months, interquartile range (IR) 143-157 in indigenous, and 145.5 months, IR 139-153 in non-indigenous girls (p = 0.04). The indigenous females showed a higher prevalence of overweight (36.4% vs 23.1%), although the frequency of obesity was similar (16.8% vs 16.3%). For indigenous girls, age of menarche was delayed by 2.69 months (confidence intervals (CI) - 0.38 to 5.77). It was observed that girls with overweight experienced age of menarche 7.59 months earlier than those with normal weight, CI -10.78 to -4.41. In the analysis of obesity, the effect on age of menarche was similar, with onset 7.53 months earlier than for the normal weight, CI -11.34 to -3.72. Conclusion: Age of menarche is younger than has been previously reported and occurs earlier in girls with overweight and obesity, while being indigenous was not related.