As the year of birth increases, the average age of menarche decreases, particularly among racial and ethnic minorities and people with low socioeconomic status.
- The average age at which menstruation begins has declined from 12.5 years in 1950 to 1969 to 11.9 years between 2000 and 2005, according to a new study.
- These trends were more pronounced among participants who identified as black, Hispanic, Asian or mixed race, and who considered themselves to be of low socioeconomic status.
- According to the authors, “childhood obesity, a risk factor for early puberty and a growing epidemic in the United States, may be a contributing factor to earlier menstruation.”
“Early menarche is associated with adverse health outcomes, such as cardiovascular disease and cancer. Yet this trend has been observed in the United States, but data remain limited on differences by sociodemographic factors and body mass index (BMI). Additionally, time to menarche and menstrual cycle regularity are other understudied characteristics,” reported scientists from the Harvard TH Chan School of Public Health (USA). That is why they conducted a study published in the journal JAMA Network Open.
71,341 women reported the age of their first period
For this work, they used the Apple Women’s Health Study dataset. A total of 71,341 American women born between 1950 and 2005 enrolled in the research between November 2018 and March 2023. They reported the age at which they started menstruating, as well as their ethnicity and socioeconomic status. Ages at menarche were defined as early (under 11 years), very early (under 9 years), and late (16 years and older). A subset of volunteers (61,932 women) reported the time it took for their menstrual cycle to become regular and was divided into five categories: up to two years, three to four years, more than five years, did not become regular, or became regular with hormone use. Another subgroup (9,865 women) reported their body mass index (BMI) at the age of menarche.
Among women born between 1950 and 1969, the age of first menstruation was 12.5 years.
The age at menarche was 12.5 years from 1950 to 1969, and the rates of early and very early menarche were 8.6% and 0.6%, respectively. Among women born between 2000 and 2005, the mean age at menarche was 11.9 years, and the rates of early and very early menarche were 15.5% and 1.4%, respectively. In both groups, the percentage of participants who had a regular menstrual cycle within two years of menarche decreased from 76% to 56%. “The magnitude of the trend toward earlier menstruation was greater among volunteers who identified as Asian, black, Hispanic, Asian or mixed race, and who considered themselves to be of low socioeconomic status,” can be read in the results of the study.
BMI: “Childhood obesity could be a contributing factor to earlier periods”
According to the authors, body mass index at the age of menarche may partly explain the trend toward earlier onset of menstruation. “In other words, childhood obesity, a risk factor for early puberty and a growing epidemic in the United States, could be a contributing factor to earlier periods.” Other potential factors, such as dietary habits, psychological stress, adverse childhood experiences, endocrine disruptors and air pollution, may also explain this trend.