Are girls’ periods starting earlier? Study says yes

The age at which girls are getting their first period seems to be trending younger—a topic that may have come up in your friend groups recently. And now, a new large-scale study published in JAMA Network Open has found evidence that backs this up. The findings also uncovered that girls’ menstrual cycles over the past 55 years are taking longer to reach “regularity”, or having a generally consistent cycle from month to month. Because starting your cycle earlier and having irregular periods for longer stretches of time can be linked to health risks later in life, experts are concerned. 

Under the umbrella of the Apple Women’s Health Study, a cohort of 71,341 participants opted in to share cycle-tracking data from their iPhones or Apple Watches about their menstrual cycles. Analyzing this self-reported data, researchers found that the average age of participants’ first period (menarche) decreased from 12.5 years for those born in 1950 to 1969 to 11.9 years for those born in 2000 to 2005. The shift is small, but marked—and echoes previous research that shows similar decreases in age at first period.

Of the 62,000 participants who reported on the regularity of their cycles, the share of those whose cycles became regular within two years of starting their period decreased from 76% to 56%. The study authors also found a two-fold increase in girls starting their periods “early” (before age 11) or “very early” (before age 9), which raises concerns that more individuals “may be vulnerable to adverse health outcomes related to early menarche,” researchers write. They also noticed a decrease in those who started their periods late. The findings were more pronounced for women of color. 

But the biggest issue is that starting your period younger can have worse health consequences down the line.

Starting periods earlier has long-term health impacts

“We found that children are experiencing longer time to regularity,” said Zifan Wang, the study’s lead author and a post doctoral research fellow at the Harvard T.H. Chan School of Public Health, to The Washington Post. “This is also very concerning because irregular cycles are an important indicator of later-in-life adverse health events. It alarms us. We need to do more early counseling and intervention on irregular cycles among children and adolescents.”

The menstrual cycle is considered a vital sign, and having irregular menstrual cycles for longer can point to long-term health risks, such as cardiovascular disease, diabetes, rheumatoid arthritis, mental health conditions and certain types of cancers, including breast cancer. Irregular cycles are also associated with premenstrual syndrome (PMS), and previous studies have found that having PMS is also a significant risk factor for postpartum depression (PPD) after giving birth. 

A longer time to cycle stability is also associated with a higher chance of irregular cycles during the rest of your reproductive years, which could be a contributing factor to fertility challenges. There’s also a correlation between girls who go through puberty at an early age and an increased risk of sexual abuse, which is important to be aware of.

Study limitations

As for whether the study findings can be applied to the general population? The answer is probably not. Because of the self-reported nature of the study, there is some risk of bias or misclassification when participants are asked to remember their experiences of menarche.

Additionally, the study was not based on a random sample: participants opted in, and must have had access to an iPhone or Apple Watch to participate, which suggests that they were of a higher socioeconomic status, all of which makes it difficult to extrapolate the results to the wider population. 

Still, there are learnings that can be drawn from the research. “Although the sample is not representative of the overall distribution of race and ethnicity in the US, the authors found that menarche was earlier and time to regularity was longer in Black participants, Asian participants, Hispanic participants, and those of other or multiple races than White participants,” writes Lauren Houghton, PhD, an epidemiologist at the Columbia University Mailman School of Public Health and the author of a commentary accompanying the study, also published in JAMA Network Open.

Why are periods starting earlier? 

What’s causing periods to start earlier and take longer to reach regularity? The contributing factors are varied. The study authors point to higher body mass index (BMI), and while that may be a factor, “pubertal timing and BMI may share a common pathway,” writes Dr. Houghton, it’s not the only one. “The authors note that decreases [in menarche age] occurred before the population increase in obesity rates, indicating that the common narrative that obesity is the driving factor is too simplistic,” she says. Instead, Dr. Houghton argues, it could be stress-related. “It is very likely that BMI and stress interact to accelerate age at menarche and prolong cycle regularity. My working hypothesis is that more stress increases the pool of androgens and more adipose tissue converts the abundance of androgens into estrogens, leading to earlier puberty.” 

Socioeconomic and environmental factors may also be at play: including exposure to endocrine-disrupting chemicals such as PFAS, as well as psychosocial factors and systemic barriers that are often faced by people of color. It’s clear that more research is needed to investigate the factors behind period onset. As we know, women’s health and menstrual health are significantly underfunded areas of study.

Start having period conversations early

Having early and frequent conversations with kids about periods and puberty can be helpful, as education is key. Read books about periods with kids, like the new “A Kids Book About: Periods” by Jessica Biel, no matter their gender, to help normalize conversations around menstruation. 

Talking more about periods and puberty can help kids embrace their period and see it as something to celebrate rather than fear it or be ashamed of it. Help kids learn to look out for early signs, and help them feel prepared and knowledgeable about their changing body and what this new life stage means for them. Celebrate their first period with them to mark it as a special occasion. 

Finally, encourage those getting their period to track their cycles, whether that’s using an app or a journal or notebook. The important thing is to remember that menstrual data is health information—and can help young girls listen to the signals their body is sending them and encourage them to be strong advocates for their own care, both now and as they get older.