Girls in the United States are getting their periods earlier, and it's taking longer for them to become regular, according to a new study.
The age at which women get their first period, known scientifically as "menarche," is influenced by a range of genetic and environmental factors. While some variation is natural and normal, we are increasingly learning that early-onset puberty is associated with an increased risk of various adverse health outcomes, including heart problems, lung disease, and dementia.
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This is concerning as, according to new research from Harvard University, the average age of a first period in the United States has decreased from 12.5 to 11.9. What's more, the number of girls whose first period is classified as "early" (under the age of 11) has nearly doubled.
"Despite a relatively small magnitude of change in mean age, our study is among the first to show that the percentages of early and very early menarche have also increased by almost 2-fold across birth years from 1950 to 2005, raising concerns that more individuals may be vulnerable to adverse health outcomes related to early menarche," the researchers write.
The study, published in the journal JAMA Network Open, analyzed data from over 71,000 American females born between 1950 and 2005, including information about their menstrual cycles, ethnicity, socioeconomic status and body mass index (BMI).
Young women not only appeared to be getting their periods earlier, but menstruation was also taking longer to become regular, which poses additional health concerns.
"Having irregular cycles is associated with long-term health conditions such as mental health, cardiovascular disease, and breast cancer," Associate Professor Michelle Wise from the Department of Obstetrics and Gynecology at the University of Auckland, who was not involved in the study, said in a statement.
"In the gynaecologist office, we see heavy menstrual bleeding resulting in anaemia and poor quality of life, new diagnoses of endometrial cancer in women in their 30s and 40s, and couples having difficulty conceiving."
These trends were particularly pronounced among Black and Asian participants and those from lower socioeconomic backgrounds.
In a separate analysis, the team found that higher BMI at the age of the first period explained roughly half of this variation. This makes sense because, for periods to start, you need to have a baseline level of body fat. As childhood obesity has risen, children are reaching this body fat requirement earlier.
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But how can we explain the other half of this variation?
"Other factors need to be explored to explain these trends and disparities, including environmental factors, dietary patterns, psychosocial stress, and adverse childhood experiences," the authors said.
Previous research has shown that air pollution may be contributing to earlier puberty in girls, and microplastics have also been shown to contain hormone-disrupting chemicals that may influence when we start our first period.
Considering the health consequences associated with early-onset puberty, urgent research is needed to understand these trends. "Further awareness among health care practitioners and researchers is needed to understand the reasons for these trends and their health implications," the researchers write.
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