American girls have had their periods earlier and earlier over the past fifty years, according to new research

Over the past 50 years, girls in the United States had their first period earlier and took longer to experience regular cycles, a new study shows.

The study, published in JAMA network openedfound that the trend is especially pronounced among Black, Hispanic, Asian, and mixed-race participants, and among those who reported lower socioeconomic status.

“This is important because early menarche,” or a first period, “and irregular periods can indicate physical and psychosocial problems later in life,” says Zifan Wang, a postdoctoral researcher at Harvard University’s TH Chan School of Public Health and lead author of the study.

As of 2019, researchers from Harvard and the National Institute of Environmental Health Sciences (NIEHS) surveyed more than 71,000 participants born between 1950 and 2005 about when they got their first period, when it became regular, and for certain demographic information. Researchers then divided the group into five generational groups.

They found that women born in the oldest group, between 1950-1969, had their period at an average age of 12.5 years, compared to 11.9 years for the youngest group, born between 2000-2005.

The research was conducted via an app as part of the Apple Women’s Health Survey. This allowed researchers to contact a group multiple times, or what researchers call a longitudinal research design.

Although the study was large, it is based on self-reported information – which is generally considered less reliable than sources such as medical or financial data. In some cases, participants would have to think back decades. Still, the study will likely provide direction for future research.

In addition to a younger average age at menarche, the study found that the number of people who got their first period early (under 11) or very early (under 9) roughly doubled between the oldest and youngest generations. Of the oldest group, 8.6% had a period before the age of 11, compared to 15.5% of people in the youngest generation. Similarly, 0.6% of people in the oldest generation had a period before the age of nine, compared to 1.4% in the youngest generation.

“We certainly see patients who start menstruating at age 9 or 10,” says Dr. Anne-Marie Amies Oelschlager, a pediatric gynecologist at the University of Washington School of Medicine, and president of the American College of Obstetricians and Gynecologists (ACOG). ) clinical consensus committee for gynaecology.

She continued: “Even though this is kept within normal limits, it is quite distressing for our patients and their parents. They are still in primary school, in third or fourth grade, and it is difficult to master the periods in third or fourth grade.”

Importantly, menarche at a younger age may not be pathological. Amies Oelschlager said better sanitation and nutrition are likely at least part of the reason girls are getting their periods earlier, both in the U.S. and globally.

“If a person shows signs of puberty before the age of eight, he should talk to his doctor about it, and if he has not had a period by age 15, he should also talk to his doctor about it,” she said . In some cases, very early puberty can be a sign of rare but serious conditions, such as brain tumors.

Can have an early period lifelong consequences. At the onset of puberty, the growth plates fuse, meaning that people who enter puberty early may not reach their maximum genetic height. It may also increase women’s risk of cardiovascular disease and breast cancer.

Early physiological development can also have dramatic social consequences because it does not coincide with early cognitive development. Children who experience early puberty are at increased risk of sexual violence, sexually transmitted infections and early pregnancies.

Early puberty is also associated with an increased risk of depression, anxiety, substance abuse and suicidal behavior.

Amies Oelschlager said the literature currently suggests that breast development occurs in younger American girls, but further research will be needed to confirm that menarche occurs on average in girls under age 12, as the new JAMA Network Open study suggests.

There are many factors that influence the onset of puberty, but the exact reasons for menarche and breast development at a younger age are up for debate. One hypothesis is that a higher percentage of body fat triggers the pituitary gland to produce puberty hormones. Other research has shown that body mass index is the greatest predictor of early menstruation. Scientists reason that a greater prevalence of obesity in children may explain the higher percentage of girls who have their periods early.

“What we need to ask ourselves is: why has the body mass index increased?” Dr. Frank Biro, a physician at Cincinnati Children’s Hospital Medical Center, said Scientific American. “Reduced physical activity and a higher calorie diet are likely part of the puzzle. But I think another critical component is our ubiquitous environmental exposure to endocrine-disrupting chemicals.”

Endocrine-disrupting chemicals from plastics and petrochemical pollution are found in a wide range of consumer goods, including pesticides, building materials, furniture, children’s toys, fabrics and cosmetics. Most of these are still unregulated, despite warnings from scientists about possible negative effects on human health.

Wang said a wide range of factors need to be taken into account to understand why menarche may occur in younger girls.

“These factors can include what’s in the environment, such as chemicals that affect hormones and air pollution, or dietary patterns, stress and adverse childhood experiences,” she said. “Studying these factors can help us find better ways to stop or slow these trends.”