Menarche at an Earlier Age: Results from Two National Surveys of Israeli Youth, 2003 and 2016

Study Objective: To assess emergent changes in the age at menarche and investigate associated factors in Israeli adolescents in 2003 and 2016. Design: Cross-sectional study. Setting: Two national representative school-based surveys (first and second “Mabat Youth”). Participants: Both surveys included female students in 7th-12th grades (ages 11-19 years). The first (N = 3328) was conducted between the years 2003 and 2004, and the second (N = 2535) from 2015 to 2016. Interventions: The survey questionnaire was self-administered and anthropometric measurements were performed by trained personnel. Main Outcome Measures: The current age at menarche in Israeli girls was determined and independent factors (demographic, clinical, and lifestyle) examined. Changes that occurred since the past national survey more than a decade ago were documented. Results: The estimated median age at menarche declined from 13.0 (interquartile range, 12.0-14.0) years in 2003-2004 to 12.5 (interquartile range, 12.0-13.0) years in 2015-2016 (P < .0001). Jewish girls reached menarche earlier than Arab girls, but both populations experienced a similar downward trend in the past approximately 14 years. Greater body mass index, higher socioeconomic status, and immigrant status were associated with younger menarche onset (P < .001). Age at menarche remained lower in 2015-2016 vs 2003-2004, even after adjustment for these potential confounders, with a high hazard ratio (HR), which decreased as a function of survival time (t): HR_t = 15.417 × 0.813^t. Conclusion: This study confirms the decline in age at menarche in Israel. Findings were associated with body mass index and population group but also indicated that other factors are likely involved.