The average age of onset of first menstruation has been going down in the U.S. From 1950 to 1969 the average age was 12.5. From 2000 to 2005 it dropped to 11.9.
Also, the girls with earlier onset were more likely to take longer for their periods to become regular. Typically, regular menses happen within 2 years of the onset of menstruation.
To further evaluate this change, Wang and colleagues studied 71,341 girls in the U.S. Results were published in JAMA Network Open 2024; 7(5): e2412854. Their study forms the basis for this blog post
They verified the trend for “earlier menarche (first onset of menses) and longer time to regularity over time …” They also found that this trend was more common in “non-Hispanic black, Asian, or girls of multiple races (compared with non-Hispanic White individuals) and among low socioeconomic groups.”
The percent of girls with early onset (less than age 11) was 8.6% but increased to 15.5%. The incidence of very early onset (less than age 9) went from 0.6% to 1.4%.
Why does this matter? From a medical perspective it is because early onset of menses is associated with adverse health outcomes (cardiovascular disease, cancer, spontaneous abortion, and premature death).
A longer time to having regular periods is associated with other medical concerns: “decreased fecundability (able to get pregnant), longer menstrual cycles, increased risk of metabolic conditions, and all-cause mortality.”
Why is the age of onset decreasing? The researchers point out that obesity is a “risk factor for early onset puberty.” They found that “body mass index at menarche partially mediated the trend for earlier menarche.”
Others have suggested that female sex hormones in food may play a role. Even if true, we do know that overweight and obesity have become more common in recent years so that contribution to the problem is more certain.
The researchers also pointed out that early onset of menses is more common among certain minorities and individuals from lower socioeconomic groups, which may contribute to health disparities in the U.S.
Peter M. Hartmann, MD
Family Medicine & Psychiatry
