Secular Trend in Age at Menarche and Associated Determinants in the Valencian Population (Spain).

OBJECTIVE: To assess secular trend in age at menarche spanning nearly eight decades and to explore variations in these patterns according to selected sociodemographic and anthropometric determinants in the Valencian Community, Spain. MATERIALS AND METHODS: This population-based study included 417 260 participants born between 1931 and 2008. First, secular trend in age at menarche were assessed using time-series models across 5-year birth cohorts for the overall population. Then, 5-year birth cohorts were combined into two groups based on the data availability for the determinant analyses: an earlier-born group (1941-1975), whose age at menarche was reported retrospectively in adulthood, and a later-born group (1991-2005), whose age at menarche was collected during childhood and/or adolescence. Bayesian linear regression models were fitted for each group, adjusting for 5-year birth cohort and continent of birth in all models, and additionally for educational level in the earlier-born group and body mass index (BMI) in the later-born group. RESULTS: Mean age at menarche decreased by 1.9 years, from 13.1 to 11.1, between the 1931-1935 and 2006-2008 birth cohorts, with a steeper decline after 1975. Compared with European-born participants, those born in South/Central America (β [95% CI]: 0.33 [0.30, 0.36] years) and Africa (0.52 [0.45, 0.58] years) experienced later menarche in the earlier-born group, whereas those born in South/Central America experienced earlier menarche in the later-born group (-0.18 [-0.28, -0.09] years). In the later-born group, lower BMI was associated with later menarche (0.96 [0.74, 1.18] years) whereas higher BMI with earlier onset (-0.53 [-0.57, -0.48] years). CONCLUSION: There was a marked decline in age at menarche in the Valencian Community. Factors associated with age at menarche included continent of birth (with cohort-specific effects) and BMI.