PARIS, June 8 — At what age do girls start menstruating? A new study reports that the average age of the onset of menstruation for girls born between 2000 and 2005 is 11.9, compared with 12.5 for those born between 1950 and 1969.

And this is not without health risks for the women concerned — in the case of this study, young girls and women in the US.

Among other things, this research sought to gain a better understanding of menstrual health, so that appropriate action can be taken to support young girls and women throughout their lives.

Conducted by researchers at the Harvard T.H. Chan School of Public Health, in partnership with Apple and the National Institute of Environmental Health Sciences, the study set out to determine the age of menarche — the onset of the first menstrual period — in younger generations, to compare it with that of previous generations, and to evaluate the time it takes for the menstrual cycle to become regular.

The researchers also took into account the racial and socioeconomic backgrounds of participants included in this research.

This study is based on data from the Apple Women’s Health Study, including 71,341 participants enrolled between November 2018 and March 2023, who themselves provided information on the age at which they first menstruated, their race and socioeconomic status.

The scientists then divided the participants into several age brackets: those born between 1950 and 1969; between 1970 and 1979; between 1980 and 1989; between 1990 and 1999; and between 2000 and 2005.

Age of menarche was defined as early before age 11, very early before age 9, and late at age 16 and over.

Periods arriving earlier

Published in the journal, JAMA Network Open, the study reveals that the younger the girls — and therefore the younger the generation — the lower the age at which menstruation begins.

The researchers point out that the average age of menarche is estimated at 12.5 years for participants born between 1950 and 1969, compared to 11.9 years for those born between 2000 and 2005.

This may seem a small difference, but it nonetheless reflects an evolution, with potential consequences for menstrual health.

Last but not least, the rates of early and very early menarche were estimated at 8.6 per cent and 0.6 per cent respectively for participants born between 1950 and 1969, compared to 15.5 per cent and 1.4 per cent for those born between 2000 and 2005.

The authors asked a subset of participants — 61,932 women and girls — to provide information about the length of time it took to establish a regular cycle after the onset of menstruation.

Again, they were divided into several categories: up to two years; between three and four years; more than five years; never became regular; or became regular but via the use of hormones.

This data enable the scientists to observe that, the younger the participants, the greater the time elapsed between menarche and regularity of cycle (76 per cent of participants born between 1950 and 1969 reported within two years, compared to 56 per cent of those born between 2000 and 2005).

It should be noted that these trends were present among all the women and girls included in the study, but they proved even more pronounced for those identifying as Black, Hispanic, Asian or mixed-race, as well as for those who considered themselves to have a low socio-economic status.

Could weight play a role?

A third and final subgroup of 9,865 participants was asked to provide information on their body mass index (BMI) at the time of menarche.

This data enabled the scientists to suggest a potential link between childhood obesity and early menarche, even though the study was observational and did not establish a direct cause-and-effect relationship.

The authors also suggest that eating habits, psychological stress and environmental factors may play a role in the early onset of periods.

"Continuing to investigate early menarche and its drivers is critical. 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,” warns corresponding author, Zifan Wang, quoted in a news release. — ETX Studio