Decline in age at menarche among Spanish women born from 1925 to 1962.

Background: While the timing of reproductive events varies across populations, a downward trend in age at menarche has nevertheless been reported in most of the developed world over the past century. Given the impact of change in age at menarche on health conditions, this study sought to examine secular trends in age at menarche among women living in Navarre (Northern Spain) who participated in a population-based breast cancer screening programme.

Methods: The study was based on 110545 women born from 1925 to 1962.