The menstrual cycle usually begins in the early teens, between the ages of 11 and 15, although some girls begin earlier or later. The first menstrual bleeding is called menarche (MEH-nar-kee). The timing of menarche appears to be related to heredity, general health, and altitude (average menarche is earlier in lower altitudes) and occurs during a time of other changes in body size and development. The age of menarche for girls in the United States is almost a year earlier for girls born after 1980 (12.4 years of age) compared to girls born before 1920 (13.3 years of age). Researchers attribute the decrease in age of first menses to the increase in the number of girls who are overweight—16% of girls who are currently 6 to 11 years old are overweight, compared to 4% prior to the 1970s. Fat cells produce a hormone, leptin, which supports reproductive functions and is likely the primary cause of earlier menstruation. Exposure to chemicals in the environment that have estrogenic effects in the body may also be a significant factor (Ginty, 2007).
Differences in the age of menarche are often a concern for young women, especially those who begin earlier or later than the norm. Many young women, and most young men, are still not fully informed about the developments and changes that accompany the onset of menstruation, and that lack of knowledge can result in confusion and apprehension. Menstrual cycles end at menopause, which in most women occurs between the ages of 45 and 55.