Age at menarche falling, with longer time to cycle regularity: Apple Women’s Health Study

Key takeaways:

• Age at menarche has fallen from a mean of 12.5 years to 11.9 years from 1950 to 2005.
• BMI at time of menarche may partially explain the trend, but more research is needed.

Age at menarche has fallen among U.S. women during the past 55 years while time to menstrual cycle regularity has increased, both troubling signs that indicate worsening health outcomes over time, researchers reported.

“Despite a relatively small magnitude of change in mean age, our study is among the first to show that the percentages of early and very early menarche have also increased by almost twofold across birth years from 1950 to 2005, raising concerns that more individuals may be vulnerable to adverse health outcomes related to early menarche,” Zifan Wang, PhD, a postdoctoral research fellow with the Apple Women’s Health Study at the Harvard T.H. Chan School of Public Health, and colleagues wrote in JAMA Network Open. “Late menarche has decreased, which may have other health implications, such as the decreasing rates of fractures.”

Menstrual cycle data from an app

The researchers analyzed data from 71,341 women participating in the ongoing Apple Women’s Health Study who provided menstrual data via an app from November 2019 to March 2023. The mean age at menarche for the cohort was 12.2 years; the racial makeup was 69.4% white; 6.9% Hispanic; 5.1% Black and 3.1% Asian. Researchers stratified the cohort by birth year decades (1950-1969; 1970-1979; 1980-1989; 1990-1999; and 2000-2005). The primary outcomes were age at menarche and time to regularity, assessed via self-recall at enrollment. Researchers also assessed early menarche (aged 11 years); very early menarche (aged 9 years); and late menarche (aged 16 years).

Zifan Wang

Researchers found that the mean age at menarche decreased from 12.5 years in 1950-1969 to 11.9 years in 2000-2005. The number of people experiencing early menarche increased from 8.6% to 15.5%; the number of people experiencing very early menarche increased from 0.6% to 1.4% and the number of people experiencing late menarche decreased from 5.5% to 1.7%.

Among 61,932 women with available data on time to menstrual regularity, the number who reached cycle regularity within 2 years fell from 76.3% to 56%, whereas the number of people not yet in regular cycles increased from 3.4% to 18.9%. These trends were greatest among Asian and Black women or women of other or multiple races compared with white women (P for interaction = .003) and were also greatest among women with a self-rated low vs. high socioeconomic status (P for interaction < .001), according to the researchers.

Additionally, among 9,865 women who provided BMI data, researchers found in exploratory mediation analyses that 46% of the temporal trend in age at menarche was explained by BMI.

“Early menarche and longer time to regular cycles are associated with higher risk of many adverse health outcomes, such as cardiovascular disease and cancer,” Wang told Healio. “To address these health concerns — which our findings suggest may increasingly impact more individuals, particularly those in disadvantaged populations — we need significantly greater investment in early counseling, education around menstrual health as a vital sign, and individualized healthcare plans.”

Wang said more research is needed on other factors that may be causing earlier age at first period and longer intervals to establish regular periods.

“These factors may include what is in the environment, like chemicals that affect hormones and air pollution, or dietary patterns, stress and adverse childhood experiences,” Wang told Healio. “Studying these factors could help us find better ways to stop or slow down these trends.”

Higher risk for adverse health outcomes

In a related editorial published in JAMA Network Open, Lauren C. Houghton, PhD, of the department of epidemiology at Columbia University, wrote that the observed decrease in age at menarche and the longer window of time to achieve regular cycling indicate that women born in later decades may be at higher risk for adverse health outcomes than previous cohorts. Houghton highlighted “steep increases” in early-onset breast cancer from 1976 to 2006 among women aged 25 to 40 years, representing the same birth cohort who reached menarche at age 12.5 years from 1950 to 1969 in the study.

“This finding means that those born in 2000 to 2005 are individually at 20% increased risk of breast cancer because they are the first cohort, on average, to reach menarche before 12 years of age,” Houghton wrote. “At the population level, we can anticipate a markedly higher incidence of early-onset breast cancer in 2033 compared with 2006, which is less than 10 years away. This is a crude projection but a harbinger for menstrual health to be the next vital sign.”

Reference:

• Houghton LC. JAMA Netw Open. 2024:doi:10.1001/jamanetworkopen.2024.12778.

For more information:

Zifan Wang, PhD, can be reached at zwang@hsph.harvard.edu; X (Twitter): @zifan_wang.