A new study published on May 29 in JAMA Network Open revealed that the median age at menarche has remained relatively stable at around 12 years, and the proportion of girls starting menstruation before age 11 has significantly increased over time.
Menarche, or the first menstrual period, marks the beginning of the monthly hormonal cycle and reproductive lifespan. Additionally, it signifies the end of female puberty.
Researchers with the Harvard T.H. Chan School of Public Health’s Apple Women’s Health Study examined data from more than 71,000 U.S. women born between 1950 and 2005, encompassing various ethnicities and socioeconomic backgrounds. They aimed to determine the age at which these women experienced their first menstrual cycle and how long it took for their cycle to become regular.
The study found that nearly 16 percent of women born between 2000 and 2005 started their menstrual cycles between ages 9 and 11, compared to almost 9 percent of those born between 1950 and 1969. Additionally, researchers observed an increase in the number of women experiencing irregular menstrual cycles for three years or more after menarche.
When stratifying trends by race and ethnicity, participants who were Asian, Hispanic, non-Hispanic black, or of other or multiple races or ethnicities were consistently more likely to experience early menarche than non-Hispanic white participants.
An exploratory analysis of a subset of 9,865 participants estimated that 46 percent of the trend could be attributed to body mass index—a measure of a person’s body fat based on height and weight. The authors noted that obesity is a risk factor for early-onset puberty and that childhood obesity is on the rise in the United States, which could explain the trend toward earlier menarche. However, it’s unknown to what extent changes in early BMI affect the trend. The underlying cause of the remaining 54 percent experiencing early menarche remains unclear.
Menstrual Cycle Considered Vital Sign of Health
The American College of Obstetricians and Gynecologists (ACOG) considers the menstrual cycle to be a vital sign of overall health, and irregularities can indicate underlying health issues, such as hormonal imbalances, thyroid disorders, or other medical conditions. The menstrual cycle also involves the immune system as uterine immune cells undergo substantial changes and facilitate the thickening and thinning of the uterine lining.
According to ACOG, girls typically have their first period between 12 and 13 years of age, but it takes a few years for menstrual cycles to become regular. Until then, adolescents may experience irregular periods as their bodies adjust to new hormonal patterns.
Early Periods May Cause Health Problems
A growing body of evidence, including the current study, links early menarche and a longer time to regularity with an increased risk of health conditions, such as cardiovascular diseases, cancers, diabetes, asthma, multiple sclerosis, metabolic conditions, and all-cause mortality.
A 2021 study published in the Annals of Epidemiology found that earlier menarche in girls and a longer time to reach menstrual regularity were associated with an increased risk of all-cause and cause-specific mortality. Girls who started their first period at age 11 or younger were at an increased risk of death from diabetes, breast cancer, and other cancers compared to those who had their first period at 13 years.
A 2021 study in Cancer Research found that early exposure to sex hormones associated with early-onset menstruation is associated with an increased risk of seven cancers in middle-aged women.
A 2020 systematic review and meta-analysis of 28 studies in PLOS Medicine found that girls who experience earlier menarche have an increased risk of Type 2 diabetes and impaired glucose tolerance in adulthood.
In a meta-analysis of eight prospective studies involving 4,553 subjects with endometrial cancer, researchers found that an earlier age of menarche is associated with an increased risk of endometrial cancer. Likewise, a previous study by the same authors found a “statistically significant inverse association” between ovarian cancer and later menarcheal age.
Evidence also suggests early menarche may enhance multiple sclerosis disease activity in children. In a Canadian prospective study, researchers found a 36 percent decrease in the probability of having a diagnosis of multiple sclerosis for each year menarche was delayed, although a delayed-onset menstrual cycle accompanies its adverse health problems.
