Why More Girls Are Starting Puberty Earlier — Scientists Reveal the Surprising Cause

The age at which girls in the United States experience their first menstruation, known as menarche, is decreasing compared to past generations. This trend is especially evident among racial minority groups and individuals from lower-income backgrounds. The shift has raised concerns and led researchers to investigate the underlying causes behind this change.

The Changing Timeline of Menstruation in Girls

Over the past few decades, there has been a notable and concerning shift in the age at which girls begin menstruating. Increasingly, girls are experiencing menarche—the onset of their first period—at younger ages, and it is taking longer for their menstrual cycles to become regular. This trend raises significant public health concerns, as early and irregular menstruation can signal broader issues affecting the health and well-being of women and girls, with possible long-term consequences.

To better understand this phenomenon, researchers analyzed data from the Apple Women’s Health Study, which included 71,341 participants who self-reported details such as their age at menarche, race, and socioeconomic status. Participants were grouped into five birth cohorts spanning from 1950 to 2005, and their menarche was categorized as very early (before age 9), early (before age 11), or late (age 16 or older).

A portion of participants also provided information on how long it took for their menstrual cycles to become regular. Findings revealed a significant decline in the proportion of girls whose cycles regulated within two years of their first period. In addition, another subset reported their Body Mass Index (BMI) at the time of menarche, allowing researchers to examine potential correlations between BMI and menstrual trends.

This comprehensive analysis offers important insights into the evolving patterns of menarche in the United States and highlights the need for further investigation into the social, environmental, and biological factors contributing to these changes.

Insights from the Research

The study identified a clear link between participants’ birth years and the age at which they experienced menarche. Specifically, younger generations showed a decline in the average age of their first period compared to older cohorts, indicating that girls today are beginning menstruation earlier than those in past decades. Additionally, the time it took for menstrual cycles to become regular increased in more recent birth groups. In other words, not only are girls starting their periods at younger ages, but it is also taking them longer to establish a regular cycle.

A particularly notable finding was the increase in both early and very early menarche among girls born between 2000 and 2005. While these patterns were evident across all sociodemographic groups, they were most pronounced among racially diverse and lower-income participants.

Unpacking the Reasons for Early Onset of Menstruation

The study identified several factors that appear to influence the age at which girls begin menstruating. These include dietary habits, psychological stress, exposure to childhood trauma, and environmental influences such as endocrine-disrupting chemicals and air pollution. Among these, Body Mass Index (BMI) stood out as the most significant factor. Higher BMI at the time of menarche was strongly linked to earlier onset, with childhood obesity emerging as a key contributor to premature puberty.

Beyond the timing of menarche, these factors may also affect other aspects of menstrual health—such as how long it takes for cycles to become regular, the intensity or discomfort of periods, and even the age of menopause. These impacts carry serious implications for the overall health and lifespan of women and girls.

The Health Implications of Early Menses

Beyond simply extending the number of years a woman experiences monthly periods, early menarche has serious implications for long-term health. It is linked to a higher risk of several major health conditions, including breast, ovarian, and endometrial cancers. In addition, women who begin menstruating at an earlier age are more likely to develop cardiovascular issues, such as heart disease and stroke.

Fertility can also be affected. Early onset of menstruation is associated with an increased risk of developing polycystic ovary syndrome (PCOS), a hormonal disorder that can lead to infertility and various metabolic and reproductive complications.

One of the primary reasons early menarche is tied to a greater cancer risk is prolonged exposure to estrogen. Estrogen—a hormone produced by the ovaries, adrenal glands, and fat tissue—can promote the growth of hormone-sensitive cancer cells. The earlier menstruation begins, the longer a woman’s body is exposed to estrogen over her lifetime. Moreover, individuals with higher body fat tend to produce more estrogen, which further increases the risk of hormone-related cancers, including breast, endometrial, and ovarian cancer.

How to Address the Risks of Early Menarche

Based on these findings, girls and women can take proactive measures to reduce the effects of early menarche. Maintaining a healthy lifestyle—with balanced nutrition and regular physical activity—can help regulate weight and may even delay the onset of menstruation. Managing stress, getting enough restful sleep, and limiting exposure to environmental toxins like endocrine-disrupting chemicals are also important steps for supporting menstrual health. Together, these actions can help lower the risk of health issues linked to early puberty.

Regulatory Interventions for Improving Women’s Health

While women and girls play a vital role in safeguarding their health, the responsibility to address early menarche also lies with the government and regulatory agencies. They can take important steps by:

Enacting policies that encourage healthy lifestyles, emphasizing balanced nutrition and regular physical activity.
Ensuring that all women have access to affordable, high-quality healthcare services.
Regulating and limiting the use of endocrine-disrupting chemicals in everyday consumer products.
Providing educational resources and support for girls and women experiencing early menarche.
Funding and supporting research into the causes of early menarche, with a focus on environmental factors like endocrine disruptors.
Implementing policies aimed at improving environmental quality, including reducing air pollution and tightening regulations on chemicals found in crops, water, food products, cleaning agents, clothing, and more.

These collective efforts are essential for protecting the health of current and future generations of women.

Summary and Implications

Ongoing research continues to shed light on the complex factors and health consequences linked to early menarche, underscoring the urgent need to prioritize menstrual health in both science and public policy. By increasing awareness, promoting healthy lifestyle choices, and supporting targeted interventions, girls and women can better manage the challenges associated with early puberty and work toward improved menstrual health and overall well-being.

Why More Girls Are Starting Puberty Earlier — Scientists Reveal the Surprising Cause