Research shows that the average age of the first menstruation drops to 11.9 years

Menstration is a critical indicator of health. Whether and when someone with a uterus gets their period – for the first time and throughout their life – can reflect not only reproductive health, but also the risk of cardiovascular disease, cancer, miscarriage and premature death.

This also makes menstruation a useful measure of public health. And digital tools for clinical research are beginning to shed light on the extent to which periods change over time.

a study published Wednesday in JAMA Network OpenBased on data from more than 71,000 women collected through the Apple Research App, it shows that over the past 55 years, girls in the United States have gotten their first period earlier and earlier — and it has taken longer for their periods to become regular, indicating a worsening general reproductive health and public health.

The research is part of the large Apple Women’s Health Study, launched in 2019 and conducted in collaboration with the National Institutes of Health and the Harvard TH Chan School of Public Health. They found that the average age at menarche – when an individual gets their first period – fell from 12.5 years in 1950 to 1969 to 11.9 years in 2000 to 2005. Over the same period, the percentage of people experiencing early menarche fell ( before age 11) increased from 8.6% to 15.5%, and the percentage of those with very early menarche (before age 9) more than doubled from 0.6% to 1.4 %.

Among the 62,000 participants who shared cycle regularity data, the percentage whose cycles became regular within two years of menarche fell by 74% to 56% between 1950-1969 and 2000-2005.

Both early menarche and irregular cycles are associated with health problems. An early first period is associated with an increased risk of cardiovascular disease, cancer and premature death, usually related to increased estrogen exposure. And a longer period to achieve cycle stability in the early years is associated with a greater likelihood of irregular cycles throughout the rest of reproductive life, which can be a cause of infertility.

It is not exactly clear why the experience of menstruation changes so much. “The determinants of menarche and the transition to puberty are multifactorial,” co-author Shruthi Mahalingaiah, assistant professor of environmental, reproductive and women’s health at Harvard, wrote in an email to STAT. They may be related to body composition, diet, physical activity and stress, along with environmental exposure to endocrine-disrupting chemicals and air pollutants.

But the research offers clues. About 10,000 participants provided data on their body mass index, and the analysis estimated that about 46% of the decline in menarche could be explained by higher BMI, in part because puberty depends on the accumulation of sufficient body fat.

“I think this is a good reflection of the obesity epidemic that we’re seeing right now,” said Aviva Sopher, professor of pediatrics at Columbia University Irving Medical Center, who was not involved in the study. She suggested that the changes could be related to a possible increase in polycystic ovary syndrome. “To me, this is also concerning, this kind of coincidence of obesity and earlier puberty and more irregular cycles,” she said.

Obesity may not tell the whole story. “I think obesity is a factor. I don’t think that fully explained the trends,” said Lauren Houghton, an epidemiologist at the Columbia University Mailman School of Public Health and a book author. commentary on the study, also published in JAMA Network Open. This study used a one-time measurement of BMI close to the age of menarche; To validate the link, she said, researchers should conduct prospective longitudinal studies of age at menarche and body mass.

“Another concern is stress and the effect of stress on earlier puberty and earlier menarche,” said Houghton, who highlighted that stress during Covid-19 was linked to younger age at puberty. Stress can also be caused by environmental factors such as financial instability or racism: in the study, racial and ethnic minority groups and people of lower socioeconomic status were most likely to experience cycle irregularities and a reduction in the age of first menstruation.

Early menarche can also be a cause of further stress over time, said Sopher, who has researched the psychological consequences of early menstruation. “If more girls go through puberty earlier, it could become more comfortable for those experiencing puberty,” she said. “But on the other hand, girls who enter puberty earlier are generally at increased risk of sexual abuse because they look very mature but are still immature.”

Overall, the study is an important reminder of the value of menstrual data as a health indicator, Houghton said. “For most of history, people have viewed menstruation as noise or a nuisance,” she said. But as individuals have started using wearables and mobile apps to track their cycles more regularly, menstruation allows people to better understand their own unique cycle, she said.

For example, someone who has a consistently short cycle may want to bring a change in length to the attention of a medical provider, even though it still seems like a “normal” 28-day cycle. For providers, the data provides important information about a person’s health, including possible reproductive and endocrine problems.

And for population-level health researchers, large-scale data like that from the Apple Women’s Health Study offers the opportunity to understand factors that influence menstruation and fertility trends — including the reproductive health of gender-diverse populations, Houghton said — and what kinds of systemic interventions are necessary to improve this.

Menstrual variation could be used to improve diagnostics and, for example, to provide a better picture of individual health and public health. “We know that cardiovascular disease biomarkers differ depending on where you are in your menstrual cycle, and that this can lead to misdiagnosis and underdiagnosis,” says Houghton; The quality of the mammogram also varies by menstrual stage.

Menstrual health and women’s health are understudied and underfunded. “We need significantly more investment in early counseling, education about menstrual health as a vital sign, and individualized health care plans,” Mahalingaiah wrote.

“We’re making progress right now…but that doesn’t make up for the decades of under-research,” Houghton added. “And so the ability to use the app data is great for me. It allows me to do research that I could never do before – and without funding.”