Periods arriving earlier for younger generations | News | Harvard T.H. Chan School of Public Health
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Boston, MA—The average age at menarche—the first menstrual period—has been decreasing among younger generations in the U.S., especially those belonging to racial minorities and lower socioeconomic statuses, according to a new study led by researchers at Harvard T.H. Chan School of Public Health. It also found that the average time it takes for the menstrual cycle to become regular is increasing.
The study was published on May 29 in JAMA Network Open. It is the latest publication from the Apple Women's Health Study, a longitudinal study of menstrual cycles, gynecological conditions, and overall women's health conducted by Harvard Chan School, the National Institute of Environmental Health Sciences, and Apple.
"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, assistant professor of environmental, reproductive, and women's health at Harvard Chan School.
While previous studies have shown trends towards earlier menarche over the past five decades, data has been limited on how these trends present within different racial groups and socioeconomic statuses. Additionally, few studies have had sufficient data to identify any trends regarding time to menstrual cycle regularity.
The researchers used the Apple Women's Health Study's large, diverse dataset to fill this research gap. Participants who enrolled in the study between November 2018 and March 2023—71,341 in total—self-reported the age at which they first began menstruating and their race and socioeconomic status. The researchers divided the participants into five age brackets: born between 1950-1969, 1970-1979, 1980-1989, 1990-1999, and 2000-2005. Ages of menarche were defined as early (younger than 11 years old), very early (younger than 9), and late (ages 16 and above). A subset of participants (61,932) self-reported the time it took for their menstrual cycle to become regular and were divided into five categories: up to two years, between three and four years, longer than five years, hasn't become regular, or became regular with use of hormones. Another subset (9,865) provided their body mass index (BMI) at their age of menarche.
The study found that as birth year increased (meaning younger participants), average age at menarche decreased and time from menarche to menstrual cycle regularity increased. Among participants born from 1950-1969, the average age at menarche was 12.5 years, and the rates of early and very early menarche were 8.6% and 0.6%, respectively. Among participants born from 2000-2005, the average age of menarche was 11.9 years, and the rates of early and very early menarche were 15.5% and 1.4%, respectively. Across the two groups, the percentage of participants who reached menstrual cycle regularity within two years of menarche decreased from 76% to 56%. The researchers observed that these trends were present among all sociodemographic groups but were most pronounced among the participants who identified as Black, Hispanic, Asian, or mixed race, and who rated themselves as belonging to a low socioeconomic status.
The findings showed that BMI at age of menarche could explain part of the trend toward periods starting earlier—in other words, that childhoodobesity, a risk factor for early puberty and a growing epidemic in the U.S., could be a contributing factor to earlier menarche. Other possible factors that might explain the trend include dietary patterns, psychological stress and adverse childhood experiences, and environmental factors such as endocrine-disrupting chemicals and air pollution.
"Continuing to investigate early menarche and its drivers is critical," said corresponding author Zifan Wang, postdoctoral research fellow in Harvard Chan School's Department of Environmental Health. "Early menarche is associated with higher risk of adverse health outcomes, such as cardiovascular disease and cancer. 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."
The authors noted some limitations to the study, including that it relies heavily on retrospective self-reporting.
Other Harvard Chan School authors included Gowtham Asokan, Jukka-Pekka Onnela, Michelle Williams, Russ Hauser, and Brent Coull.
The study was made possible by funding from Apple, Inc. and the National Institutes of Health (grant Z01ES103333).
"Menarche and time to cycle regularity among females born between 1950-2005 in the US," Zifan Wang, Gowtham Asokan, Jukka-Pekka Onnela, Donna D. Baird, Anne Marie Z. Jukic, Allen J. Wilcox, Christine L. Curry, Tyler Fischer-Colbrie, Michelle A. Williams, Russ Hauser, Brent A. Coull, Shruthi Mahalingaiah, JAMA Network Open, May 29, 2024, doi: 10.1001/jamanetworkopen.2024.12854
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By Maya Brownstein
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Girls are getting their first menstrual cycle younger and younger...
Part of climate change.
No, child obesity and hormones in food are the reasons blamed. The growth hormones in beef, chicken and pork are absorbed...
Certainly you're not implying that girls are fatter now?.....
Girls and boys are considerably more obese now than before.
I've heard about this earlier onset phenomenon for many years. Yes, it is due to hormones (and "hormone mimickers) in food.
The food industry gets them into animals so they grow quicker. (And its also makes the animals fatter).
Whether he's implying it or not it is a fact. (But the focus of this discussion is on hormones and reaching puberty earlier, both boys and girls are much, much fatter when I was a kid.
I was mildly overweight until Jr High when I grew and started playing sports, but it has always been a struggle made more difficult by being heavy as a child. Today morbid obesity is common in children. Lack of outdoor activity is a factor too.
Fast food, processed food, cereals, sugary drinks and that parents are too busy to prepare healthy meals are all contributing factors.
Disneyland had to expand the size of ride seats because if it!
And those are volunteers who you would think were in better than average shape to begin with. I recently spoke to an old basketball coach who told me we were light-years ahead of the current batch of high-schoolers regarding physical fitness...
Why do you think that could be?...
Why do you think it is a fact? Doctors blame childhood obesity which has long been blamed on the poor nutrition among poorer Americans whose dollars go a lot farther on fattening carbs than fresh fruit, fresh vegetables and quality protein. There are also biological differences.
It is true that its worse amongst poorer people.
However over the years its gotten worse amongst Americans in all income brackets.
That is true and childhood obesity is highly likely to extend into adulthood as chronic diseases of diabetes and blood pressure.
When I was a kid, all children were skinny. (I thought all kids were skinny, but there always seemed to be one fat kid in every class. But only one. (We though it was some sort of rule: "Every class must have 1 fat kid--but no more then 1).
There were mainly 2 reasons most kid were not over-weight:
1. There were less chemicals in food-- (and in the water & air) back then.
2. We were constantly active-- on weekends and after school on Weekdays we used to be constantly running around, racing, playing tag. Boys playing one type of ball game or another, girls constantly jumping rope!
One of the worst things for health was modern technology-- TV-- then computers and cellphones.
There's been a lot of discussion about how the food industry uses growth hormones to fatten up animals. But there are other chemicals in food that are bad.
One of these is "BPA" (Bisphenol A). Most cans of food are lined with it. Its also used to turn hard plastic into soft plastic.(BPA is not an actual hormone but is classified as a "hormone mimicker).
Bisphenol A ( BPA ) is a chemical compound primarily used in the manufacturing of various plastics . It is a colourless solid which is soluble in most common organic solvents , but has very poor solubility in water. [ 2 ] [ 7 ] BPA is produced on an industrial scale by the condensation reaction of phenol and acetone . Global production in 2022 was estimated to be in the region of 10 million tonnes. [ 8 ]
Most food cans are lined with BPA. (Whole Foods carries some products that are not lined with BPA. (Those cans say "BPA Free" on the label. I used to buy Tomato sauce in cars-- now I only buy it in glass jars. Also Whole Foods also sells Sockeye (wild) Salmon in BPA free cans. (Wild caught Atlantic Salmon
In general some plastic bottles (for example those Vitamins are in) are OK-- some are not. You can tell by the recycling numbers on the bottom: I always look for #1 or #2. IIRC 4 & 5 are also OK. Safe: 1-2-4-5.
It is not just obesity. Many children are developing secondary sexual characteristics much easier than in prior generations...
BPA is one of many chemicals that lead to that. (I believe some of these "hormone mimickers"-- in food, in water-- in the air-- act like estrogen.)
... and this points to the need for tampons in the sixth-grade, boys' restrooms.