[Secular trends in age at menarche in relation to body mass index]

To evaluate the secular trend of menarche according to body mass index (BMI).

Six hundred and eighty five girls (7-18 years) assessed in 2001 were compared with 750 evaluated in 2010. They were grouped by BMI Z-score: (thin + normal) and (overweight + obese). Menarche was reported by status quo and age at menarche estimated by a logit model. We used the Qui-square test, Mann-Whitney test, and Logistic Regression, at a 5% significance level.

Menarche advanced 3.24 months. There was an increase in obesity, and a decrease of the prevalence of normal girls. Menarche was anticipated by 1.44 month in the thin + normal group and by 5.76 months in the overweight + obese group. There was no interaction between the effects determined by the evaluated period and nutritional diagnosis.

Although both the period and BMI influence the menarche, one cannot attribute this advance only to changes in the nutritional profile of the sample. Other factors that were not tested may also contribute to this finding.