Secular trends in age at menarche and associated determinants in the Valencian population (Spain)

BackgroundMenarche is a critical developmental milestone, with earlier onset associated with adverse long-term health consequences. Despite a reported global decline in age at menarche over the last century, this trend and its determinants remain insufficiently studied in Spain. ObjectiveTo assess secular trends in age at menarche and its determinants in the Valencian Community, Spain. MethodsThis population-based study included 417,260 participants born between 1931 and 2008. First, secular trends in age at menarche were assessed using time-series models across 5-year birth cohorts for the overall population. Then, participants were categorized as either women (born 1931-1985) or girls (born 1990-2008), and Bayesian linear regression models were fitted for each group, adjusting for birth cohort and continent of birth in all models, and additionally for educational level in women and body mass index (BMI) in girls. ResultsMean 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 to Europeans, women born in South/Central America ({beta}[95% CI]: 0.33[0.30, 0.36] years) and Africa (0.52[0.45, 0.58] years) experienced later menarche, while girls from South/Central America experienced earlier onset (-0.18[-0.28, -0.09] years). In girls, lower BMI was associated with later menarche (0.96[0.74, 1.18] years) and higher BMI with earlier onset (-0.53[-0.57, -0.48] years). ConclusionThere was a marked decline in age at menarche in the Valencian Community, with no evidence of leveling off. Key determinants included continent of birth (with cohort-specific effects) and BMI.