In recent decades, girls have been starting their periods at younger ages, with cycles taking longer to become regular. This trend signals potential health risks for women and girls.

A study using data from 71,341 participants in the Apple Women’s Health Study examined self-reported age at menarche, race, socioeconomic status, BMI, and time to menstrual regularity. Girls were grouped by birth year (1950–2005), and classified as having very early (under 9), early (under 11), or late (16+) menarche. The results showed a clear shift: younger generations tend to start menstruating earlier, and fewer girls reach regular cycles within two years.

These trends were consistent across demographics but were more pronounced among racially diverse and lower-income groups. Factors linked to early menarche include stress, diet, trauma, pollutants, and especially childhood obesity—BMI emerged as a major influence.

Early periods can lead to long-term health issues, including increased risks for breast, ovarian, and endometrial cancers, as well as heart disease and PCOS. This is largely due to prolonged estrogen exposure, which can promote cancer cell growth. Fat cells produce estrogen, so higher body fat raises this risk.

To counter these effects, girls and women are encouraged to maintain a healthy lifestyle—eating well, exercising, managing stress, getting enough sleep, and avoiding hormone-disrupting chemicals. These steps can help support menstrual health and reduce future health risks.