U.S. girls experiencing their first period (menarche) has decreased, especially among minorities

The average age at which U.S. girls experience menarche, their first menstrual period, has decreased, with certain minorities being more heavily effected

The study led by Harvard T.H. Chan School of Public Health shows that girls experiencing menarche is particularly elevated among racial minorities and those from lower socioeconomic backgrounds.

They also found that the time for menstrual cycles to become regular is increasing.

Menarche age decreasing

Menarche is the first menstrual cycle or first menstrual bleeding in humans. The research part of Apple Women’s Health Study used data from over 71,000 participants collected between November 20218 and March 2023.

Participants reported the age they first began menstruating along with their race and socioeconomic status. They were divided into five age groups, spanning both years from 1950 to 2005.

The study found that the average age at menarche has been decreasing over the years. For those born between 1950 and 1969, the average age was 12.5 years. This decreased to 11.9 years for those born between 2000 and 2005. Early menarche (younger than 11 years old) and very early menarche (younger than 9 years old) rates also increased, from 8.6% and 0.6% in the older cohort to 15.5% and 1.4% in the younger cohort.

The study revealed that the time from menarche to regular menstrual cycles has lengthened. Among participants born from 1950-1969, 76% reached menstrual regularity within two years, compared to just 56% for those born from 2000-2005.

Factors contributing to earlier periods

These trends were observed across all sociodemographic groups but were most notable among Black, Hispanic, Asian, and mixed-race participants, as well as those from lower socioeconomic backgrounds.

Researchers identified several potential factors contributing to these trends. One significant factor is BMI at the age of menarche, with childhood obesity being a known risk factor for early puberty. Other factors include dietary patterns, psychological stress, adverse childhood experiences, and exposure to environmental pollutants such as endocrine-disrupting chemicals.

“Our findings can lead to a better understanding of menstrual health across the lifespan and how our lived environment impacts this critical vital sign,” said co-principal investigator Shruthi Mahalingaiah, an assistant professor at Harvard Chan School.

Early menarche is associated with higher risks of negative health outcomes, such as cardiovascular disease and cancer. Therefor the study highlights the need for further research into the drivers of early menarche and the implications for health, especially among disadvantaged populations.

“Continuing to investigate early menarche and its drivers is critical,” emphasised corresponding author Zifan Wang. “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.”