Ian Mannix
Editor-in-Chief, Cosmos
A big study has shown that the average age for US girls to experience their first period is now under 12 years old.
The research, published today in JAMA Network Open, builds on previous studies showing that menstruation in the US and other western countries is occurring at a younger age.
The founder and managing director of Australian period product charity, Share the Dignity, Rochelle Courtenay, says its an important survey.
“When we did our 2021 Bloody Big Survey research we were surprised to find that 8.5% of girls were 10 or younger when they got their first period, but had no comparative data in other countries to see if this was normal or not. We have just completed our Bloody Big Survey again, and with over 150,000 responses we are interested to see whether the percentage of girls getting their period younger has increased or decreased when we release our report in August.”
Among participants of the latest US survey, those who were born from 1950 to 1969, the average age at menarche (the first menstrual period) was 12.5 years, and the rates of early and very early menarche were 8.6% and 0.6%, respectively.
In survey respondents born from 2000 to 2005, the average age of menarche was 11.9 years, and the rates of early and very early menarche were 15.5% and 1.4%, respectively.
And across the 2 groups, (1950 and 2000) the percentage of participants who reached menstrual cycle regularity within 2 years of menarche decreased from 76% to 56%.
In a release coinciding with the publication of the paper, the authors write: “Participants who enrolled in the study between November 2018 and March 2023—71,341 in total—self-reported the age at which they first began menstruating and their race and socioeconomic status.”
The researchers divided the participants into 5 age brackets: born between 1950-1969, 1970-1979, 1980-1989, 1990-1999, and 2000-2005. Ages of menarche were defined as early (younger than 11 years old), very early (younger than 9), and late (ages 16 and above).
A subset of participants (61,932) self-reported the time it took for their menstrual cycle to become regular and were divided into 5 categories: up to 2 years, between 3 and 4 years, longer than 5 years, hasn’t become regular, or became regular with use of hormones.
Another subset (9,865) provided their body mass index (BMI) at their age of menarche.
The trends in age of menarche and menstrual cycle regularity were present among all sociodemographic groups but were most pronounced among the participants who identified as Black, Hispanic, Asian, or mixed race, and who rated themselves as belonging to a low socioeconomic status.
The researchers say they don’t know why the age is declining, but they speculate that it could be from a number of factors:
“The findings showed that BMI at age of menarche could explain part of the trend toward periods starting earlier—in other words, that childhood obesity, a risk factor for early puberty and a growing epidemic in the U.S., could be a contributing factor to earlier menarche.
“Other possible factors that might explain the trend include dietary patterns, psychological stress and adverse childhood experiences, and environmental factors such as endocrine-disrupting chemicals and air pollution.”
“Continuing to investigate early menarche and its drivers is critical,” said corresponding author of the US study, Zifan Wang, postdoctoral research fellow in the Harvard University Chan School’s Department of Environmental Health.
“Early menarche is associated with higher risk of adverse health outcomes, such as cardiovascular disease and cancer. To address these health concerns—which our findings suggest may begin to impact more people, with disproportionate impact on already disadvantaged populations—we need much more investment in menstrual health research.”
Shruthi Mahalingaiah, assistant professor of environmental, reproductive, and women’s health at Harvard Chan School says: “Our findings can lead to a better understanding of menstrual health across the lifespan and how our lived environment impacts this critical vital sign.”
The authors noted some limitations to the study, including that it relies heavily on retrospective self-reporting.
Courtenay says: “I think they are interesting findings, there are so many moving pieces that have the potential to affect the age someone gets their first period so I would love to see more research in this space.”
Read also: do women’s periods sync?
