Girls Are Getting Their First Periods Earlier

“Our findings can lead to a better understanding of menstrual health across the lifespan and how our lived environment impacts this critical vital sign,” said co-principal investigator Shruthi Mahalingaiah, assistant professor of environmental, reproductive, and women’s health at Harvard Chan School.

Then and now

For this study, the researchers looked at data from over 71,000 women who provided relevant personal information including when they experienced menarche and how long it took them to develop a regular menstrual cycle. The women were grouped by birth decades to investigate how menstrual patterns changed over time. The data showed clear trends of younger generations starting their periods younger and taking longer to establish regular cycles. 

The research revealed that girls born between 2000 and 2005 experienced menarche at around 11.9 years old, while girls born between the 1950 and 1960s experienced menarche at around 12.5 years old. However, 15% of girls born after 2000 experienced early menarche before the age of 11, and over 1% experienced very early menarche before reaching the age of 9 years old. That is nearly double the rate seen in older generations and represents a significant difference in terms of physical development. 

Experiencing the beginning of their reproductive cycle in younger years was not the only significant finding. The research also revealed that girls today are taking longer to develop regular menstrual cycles. In the past, traditionally around 76% of girls would develop regular menstrual cycles within the first two years of menarche. Skip forward to the present day, now only around 56% of girls develop a regular menstrual cycle within two years of menarche. This irregularity can make it hard to predict cycles and plan their lives accordingly. 

What is causing the change?

According to the researchers, the findings showed that BMI at the age of menarche may explain part of the trend towards starting at younger ages. In other words, there is a potential link to childhood obesity, which is a contributing factor for the early onset of puberty,  that could be contributing to early menarche. With additional analysis, as BMI increased the researchers found a trend connecting the obesity epidemic to reproductive health. 

Other potential factors include but are not limited to dietary patterns, psychological stress, adverse experiences, and environmental factors such as endocrine-disrupting chemicals and air pollution.

Why is this important?

“Continuing to investigate early menarche and its drivers is critical,” said corresponding author Zifan Wang, postdoctoral research fellow in Harvard Chan School’s Department of Environmental Health. “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.”