Early Puberty in Girls Tied to Higher Health Risks

For decades, girls have been starting menstruation at increasingly younger ages. A new Harvard study has confirmed this trend, showing that the onset of first periods continues to occur progressively earlier. At the same time, it takes longer for menstrual cycles to become regular. This delay raises concerns about potential long-term health effects.

Researchers led by Zifan Wang, PhD, MS, from the Department of Environmental Health at Harvard T.H. Chan School of Public Health, Boston, reported these findings in JAMA Network Open. The study analyzed data from more than 70,000 women born between 1950 and 2005.

Early menarche is linked to a higher risk for obesity, type 2 diabetes, cardiovascular disease, and certain cancers, particularly breast cancer. Childhood obesity is known to promote early sexual maturation in girls, contributing to these changes.

The study was based on the Apple Women’s Health Study, a prospective digital cohort in the US. Since November 2019, users of the Apple Research app aged 18 years or older have voluntarily shared their health information for scientific research through their iPhones.

The analysis included 71,341 women who provided data between November 2019 and March 2023. Participants were divided into five groups according to year of birth: 1950-1969 (5223 women), 1970-1979 (12,226), 1980-1989 (22,086), 1990-1999 (23,894), and 2000-2005 (7912). Researchers recorded each woman’s age at menarche, time to cycle regularity, and ethnicity.

The average age at menarche steadily declined from 12.5 years in the 1950-1969 cohort to 11.9 years in the 2000-2005 cohort. The proportion of girls experiencing early menarche (before the age of 11 years) nearly doubled, from 8.6% to 15.5%. Very early menarche (before the age of 9 years) more than doubled, increasing from 0.6% to 1.4%. The proportion of patients with late menarche (age ≥ 16 years) decreased from 5.5% to 1.7%.

Among the 61,932 participants who reported regular menstruation, the proportion of those who developed a regular cycle within 2 years of menarche fell from 76.3% to 56.0%. The percentage of women without regular cycles increased from 3.4% to 18.9%.

Earlier menarche was more common among women identified as Asian, non-Hispanic Black, or of other ethnicities than among non-Hispanic White women. This trend was stronger in women with a lower socioeconomic status.

Within a subset of 9865 participants with data on BMI at menarche, 46% of the trend toward earlier menarche was linked to the BMI. Rising childhood obesity is likely to contribute to this trend. However, 54% of these changes remain unexplained.

Conclusion

“These findings suggest that early-life menstrual characteristics have been trending in directions that indicate higher risk of later adverse health outcomes, which may contribute to health disparities,” the authors wrote.

This story was translated from Medscape’s German edition.