Secular trend in age at menarche for South Korean women born between 1920 and 1986: The Ansan Study

Background: There is strong evidence of a downward secular trend in age at menarche in Europe and the USA during the last century and in Japan and China during the past few decades. However, no study on this trend in age at menarche has been reported in South Korea. Aim: To measure the trend in age at menarche in South Korea during the past few decades and the association of height with this trend. Subjects and methods: A total of 1061 South Korean women born between 1920 and 1986 were randomly recruited from Ansan Cohort Study samples and separate schoolgirl samples, and subjected to this analysis. The data on age at menarche were collected by the retrospective method. Height was measured at time studied and assumed to be relatively constant since age at menarche. Women were grouped with respect to decade of birth and mean age at menarche was determined. The secular trends in annual age at menarche and in height were analysed by the 3-year moving average. Results: Mean menarcheal age decreased from 16.8 to 12.7 years during the past 67 years, corresponding to -0.64 years per decade. Height increased from 149.23 to 161.75 cm during the same period, showing an inverse relationship in the change of trend between height and mean age at menarche. Conclusion: Our data suggest that the downward secular trend in age at menarche may reflect the secular change in physical growth in South Korean women during the past 67 years.