Decline in Age at Menarche: Results from Two National Surveys of Israeli Youths, 2003 to 2016

Background and Objectives: Since the early 19^th century, a distinct decline in the age at menarche (AAM) has been documented and is thought to have substantial public health implications. Early menstruation is linked to a variety of health problems that appear in adolescence including depression, anxiety, substance abuse and disordered eating. In addition, it is associated with chronic disease later in life and increased all-cause mortality. The goal of this study was to evaluate changes of AAM and its correlates in Israeli girls from 2003 to 2016.

Methods: Data from two national representative surveys (MABAT-Israeli Youth Health and Nutrition Survey) were analyzed and compared. Both surveys were cross-sectional, school-based studies, including students in 7^th-12^th grades. The first (n=3228) was conducted between the years 2003-2004, and the second (n=2535) from 2015-2016. Kaplan-Meier survival analysis was used to estimate the cumulative probability to reach menarche according to age. Cox proportional hazard models were applied to identify independent predictive factors of AAM.

Results: The median AAM declined from 13.0 years (IQR:12.0,14.0) in 2003-2004 to 12.5 years (IQR:12.0,13.0) in 2015-2016. Jewish girls reached menarche earlier than Arabs (p<0.001), but both populations experienced a similar downward trend in the past ~12 years. Higher BMI was associated with a younger AAM, with hazard ratio (HR) for one unit of BMI-z score of 1.19, in both surveys (p<0.001). AAM remained lower in 2015-2016 versus 2003-2004: HR=1.12 (95% CI: 1.06, 1.19), p<0.001, even after adjustment to chronological age, population group, BMI and socioeconomic status.

Conclusions: This study confirms the decline in AAM in Israel. The finding is associated with BMI and population group but also indicates that other factors are likely involved. Further studies are needed to examine the variety of causes of decreased menstrual age and efforts are needed to prevent obesity in children.