The average age of menarche (the first menstrual period) has been declining among younger generations in the U.S., especially those who belong to racial minorities and lower socioeconomic levels, according to a new study led by researchers at the School of Public Health TH Chan of Harvard. . It also found that the average time it takes for the menstrual cycle to become regular is increasing.
The study will be published May 29 in JAMA Network Open. It is the latest publication from the Apple Women’s Health Study, a longitudinal study of women’s menstrual cycles, gynecological conditions, and overall health conducted by the Harvard Chan School, the National Institute of Environmental Health Sciences, and Apple.
“Our findings may lead to a better understanding of menstrual health across the lifespan and how our living environment affects this critical vital sign,” said co-principal investigator Shruthi Mahalingaiah, assistant professor of environmental, reproductive and health health. women at Harvard Chan School.
While previous studies have shown trends toward earlier menarche over the past five decades, data have been limited on how these trends present within different racial groups and socioeconomic statuses. Furthermore, few studies have had sufficient data to identify trends regarding time to menstrual cycle regularity.
The researchers used the large and diverse data set of the Apple Women’s Health Study to fill this research gap. Participants who enrolled in the study between November 2018 and March 2023 (71,341 total) reported the age at which they first began menstruating and their race and socioeconomic status. The researchers divided the participants into five age groups: born between 1950-1969, 1970-1979, 1980-1989, 1990-1999 and 2000-2005. Ages at menarche were defined as early (under 11 years), very early (under 9 years), and late (16 years or older). A subset of participants (61,932) reported the time it took for their menstrual cycle to become regular and were divided into five categories: up to two years, between three and four years, more than five years, has not become regular, or became regular with the use of hormones. Another subset (9,865) provided their body mass index (BMI) at age of menarche.
The study found that as the year of birth increased (i.e., younger participants), the average age at menarche decreased and the time from menarche to menstrual cycle regularity increased. Among participants born between 1950 and 1969, the average age at menarche was 12.5 years, and the rates of early and very early menarche were 8.6% and 0.6%, respectively. Among participants born between 2000 and 2005, the average age at menarche was 11.9 years, and the rates of early and very early menarche were 15.5% and 1.4%, respectively. In the two groups, the percentage of participants who achieved menstrual cycle regularity within two years after menarche decreased from 76% to 56%. The researchers noted that these trends were present across all sociodemographic groups, but were most pronounced among participants who identified as black, Hispanic, Asian, or mixed race, and who considered themselves to be of low socioeconomic status.
The findings showed that BMI at age at 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 US, could be a contributing factor to earlier menarche. menarche. Other possible factors that could explain the trend include dietary patterns, psychological stress and adverse childhood experiences, and environmental factors such as endocrine-disrupting chemicals and air pollution.
“It is critical to continue investigating early menarche and its drivers,” said corresponding author Zifan Wang, a postdoctoral researcher in the Department of Environmental Health at the Harvard Chan School. “Early menarche is associated with an increased risk of adverse health outcomes, such as cardiovascular disease and cancer. To address these health problems, which our findings show may begin to affect more people, with a disproportionate impact on populations that already are at a disadvantage, we need a lot “More investment in research on menstrual health.”
The authors noted some limitations of the study, including the fact that it relies heavily on retrospective self-reports.
Other Harvard Chan School authors included Gowtham Asokan, Jukka-Pekka Onnela, Michelle Williams, Russ Hauser, and Brent Coull.
The study was made possible by funding from Apple, Inc. and the National Institutes of Health (grant Z01ES103333).