US girls are getting their first periods earlier, study finds – what's driving this?

LOS ANGELES - A recent study published in JAMA Network Open reveals that girls are experiencing their first periods at a younger age than previous generations, a trend observed worldwide.

The study, conducted by researchers from the University of Copenhagen, analyzed data from more than 71,000 women enrolled through the Apple Research App on their iPhones. 

The women were asked to recall when they first started menstruating. 

The findings indicate a significant shift in the average age of menarche, with many girls now beginning puberty as early as ten years old. On average, menstruation began at 11.9 years from 2000 to 2005, compared to 12.5 years between 1950 and 1969.

Factors contributing to earlier menstruation

Several factors may contribute to this trend, including better nutrition, increased body mass index (BMI), and exposure to environmental chemicals. 

Dr. Anders Juul, one of the study's lead authors, noted that while improved nutrition and overall health are positive developments, the early onset of puberty can pose challenges for young girls.

Implications for physical and mental health

Early menstruation is linked to a higher risk of developing specific health issues later in life, such as breast cancer and type 2 diabetes. 

Additionally, girls who mature earlier may face emotional and social challenges, including an increased risk of depression and anxiety. 

The study found that the percentage of girls getting their period before the age of 11 grew from 8.6% to 15.5%, and those who began menstruation before age nine more than doubled. This trend toward earlier periods was observed across all demographics but was more pronounced among girls from racial and ethnic minorities and those from lower-income backgrounds.

Researchers say understanding changing trends in menstruation is important because menstruation is a vital sign for health.

Experts advise parents to be proactive in discussing puberty and menstruation with their children. 

"It's important to educate caregivers, parents, and care providers on this trend so that we can also prepare our children," says Dr. Shruthi Mahalingaiah, the study’s co-author and an assistant professor of environmental, reproductive, and women’s health at Harvard T.H. Chan School of Public Health.

Resources and support

Parents can seek guidance from pediatricians and utilize educational resources to help their children navigate this developmental stage. Schools and community organizations can also play a vital role in providing support and information.

As girls begin to experience menstruation at younger ages, researchers say it is essential for parents, caregivers, and educators to be prepared to support them through this critical phase of development. 

Understanding the underlying factors and potential health implications can help address young girls' needs during their transition into adolescence.

The Associated Press contributed to this story.