A new study, published Wednesday, found that girls are starting their menstrual cycles earlier now than in previous decades. The trend is more pronounced for girls from minority groups and those from lower-income backgrounds.
The findings add to growing evidence suggesting that some girls around the world are hitting puberty earlier in life — a shift that researchers say is associated with negative health outcomes later in life but one that still can’t be fully explained. Several studies have consistently found that the decline in age seems to be steepest among racial minority groups, girls from lower socioeconomic groups and those who have higher B.M.I.s.
“In pediatric practice, there’s been kind of a trend toward just assuming that Black girls go through puberty earlier. But what’s going on and how? What are the health outcomes associated with that?” said Dr. Juliana Deardorff, head of the Maternal, Child and Adolescent Health program at University of California, Berkeley, who was not involved with the study but reviewed its findings. “We should be thinking about this, not just normalizing these disparities.”
The Background
The American College of Obstetricians and Gynecologists and other medical groups consider the onset of menstruation (known as menarche) a sign of overall health, alongside other measures like cycle regularity, blood pressure, body temperature and heart rate. Researchers have linked early menarche and persistent cycle irregularity to an increased risk of conditions later in life, like diabetes and cardiovascular disease, as well as breast and endometrial cancer.
According to ACOG, typically girls are between 12 and 13 years old when they first menstruate and it takes up to three years for their cycles to hit a regular cadence.
The Research
The new study draws on data from more than 71,000 women who used iPhones and agreed to share health information in an app. The women were born between 1950 and 2005, and of multiple ethnicities, including Black, Hispanic, Asian and white. The participants also reported on whether their socioeconomic status was low, medium or high.
Overall, the study found that while the median age at menarche hasn’t fallen too drastically, hovering around 12 years old, the share of women who started their menstrual cycles when they were younger than 11 years old increased significantly over time. Almost 16 percent of women born between 2000 and 2005 were between nine and 11 at menarche, compared to just over 8 percent of women who were born between 1950 and 1969. The study also found that more women were experiencing irregular cycles for three years or longer after menarche.
The trend toward earlier menarche age was more pronounced for Black, Hispanic and Asian women than for white women, as well as those with lower socioeconomic status. An estimated 46 percent of these declines could be explained by body mass index.
“One of the things that’s striking about this study is that, historically, everybody has attributed these changes in menstrual cycles to increases in body fat and B.M.I.,” Dr. Deardorff said. But this study underlines the fact that “even among people of healthy weight and potentially underweight, these trends are still occurring,” meaning that other factors might be at play.
Some studies have suggested that exposure to pollutants and certain chemicals can disrupt the endocrine system and the functioning of the menstrual cycle, though the evidence isn’t conclusive. Researchers have also linked early menarche to external stressors, like structural racism, abuse at a young age and financial insecurity, said Dr. Deardorff, who has co-authored several studies on how those kinds of stressors might affect puberty.
“It’s no longer controversial to say that stress can get under the skin to affect different processes,” she said, referring to the concept of weathering, an increasingly accepted theory that links exposure to chronic, prolonged stress to accelerated aging. And, Dr. Deardorff added, age of puberty or menarche should be seen “as a kind of bellwether” of the kinds of stresses that children might be facing.
The Limitations
The study was based on self-reported data, relying on participants’ memories of their first period and how long it took their period to become regular. While age of menarche is a more salient milestone that women are likely to remember later in life, “time to regularity after the onset of menarche is really tough to report retrospectively,” Dr. Deardorff said.
The study population also consists only of women who use iPhones, said Dr. Shruthi Mahalingaiah, co-author of the paper and assistant professor of environmental, reproductive and women’s health at the Harvard T.H. Chan School of Public Health. That means that the study excludes a large chunk of the U.S. population, particularly those from lower socioeconomic status, who may not use the smartphones. It is also unclear if these trends in the United States could be generalized to other populations around the world, she said.
The Takeaway
Race, socioeconomic status and B.M.I. on their own can’t fully explain the disparities in menarche timing, Dr. Deardorff said. Those three factors are inextricable from other variables that might also play a role, such as where people live, the chemical exposures they encounter and the availability of nutritious foods and access to health care. It’s really hard, then, “to tease apart what their cumulative or interactive effects might be.” Future studies, she added, should follow girls at different phases of their lives to better understand how multiple factors during puberty affect their health in adulthood.
