• Posted May 29, 2024

U.S. Girls Are Beginning Periods Earlier

U.S. girls are getting their periods at younger ages, a new study has found.

Girls born between 2000 and 2005 started their periods at an average age of 11.9 years -- a half year earlier than the average age of 12.5 years for girls born between 1950 and 1969, researchers reported May 29 in the journal JAMA Network Open.

The latest generation was also more likely to start menstruation early (15.5% versus 8.6%) and very early (1.4% versus 0.6%), results show.

Early onset of menstruation "is associated with higher risk of adverse health outcomes, such as cardiovascular disease and cancer,"said researcher Zifan Wang, a postdoctoral research fellow with the Harvard T.H. Chan School of Public Health in Boston.

The researchers found that all women are experiencing earlier menstruation, but that those who are poor or a racial minority were even more likely to start their periods at a younger age.

"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,"Wang said.

For the study, researchers analyzed data on more than 71,000 women participating in a large-scale health study. The researchers divided the women into five age brackets: born between 1950-1969, 1970-1979, 1980-1989, 1990-1999 and 2000-2005.

A girl's first menstrual period was defined as early if it occurred before age 11, very early if it occurred younger than age 9 and late if it came at age 16 or older.

Researchers found that as birth year increased, the average age of a girl's first period decreased.

They also found it is taking girls longer for their menstrual cycle to become regular.

A girl's weight appears to partially explain why periods are starting earlier, researchers said. In other words, childhood obesity -- already known to be a risk factor for early puberty -- could be contributing to earlier menstruation.

Other possible explanations include dietary patterns, stress, adverse childhood experiences and environmental factors like air pollution and chemicals that disrupt hormones.

More information

The Office on Women's Health has more about menstrual cycles.

SOURCE: Harvard T.H. Chan School of Public Health, news release, May 29, 2024