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Girls in the U.S. are getting their first menstrual period about 6 months earlier on average than they did in the 1950s and ‘60s. And more girls are beginning menstruation before the age of 9, which is considered a very early age. That’s according to a large 

 published this week in the journal JAMA Network Open.

“It's important to educate caregivers, parents and care providers on this trend so that we can also prepare our children,” says 

 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.

“The younger you are when you get your first period, it's very confusing. There's still a lot of stigma and silence around it,” Mahalingaiah says.

The study is based on data collected from more than 71,000 women enrolled through the Apple Research App on their iPhones, who were asked to recall when they first started menstruating. The researchers found that on average, menstruation was starting at 11.9 years of age in 2000 to 2005. That’s down from 12.5 years of age in the period between 1950 to 1969.

What’s more, the percentage of girls getting their period before the age of 11 grew from 8.6 percent to 15.5 percent, and those who began menstruation before age 9 more than doubled.

The study found this trend toward earlier periods across all demographics, but it was much more pronounced among girls from racial and ethnic minorities and those from lower incomes.

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

“The age at which someone starts their periods is kind of a barometer of how they're doing in general,” says 

 an assistant professor at epidemiology at Columbia University who wrote a 

The study also found more girls are taking longer to reach regular menstrual cycles. Irregular menstrual cycles are associated with several health conditions, including polycystic ovary syndrome, or PCOS. And an earlier age of first menstruation is linked to several adverse health outcomes, including a higher risk of cardiovascular disease, obesity, miscarriage and early death. It’s also linked to several cancers, including ovarian, endometrial and breast cancer.

“If someone reaches their first period before the age of 12, they are at a 20 percent increased risk for breast cancer,” Houghton says.

When you take a look at populations, that becomes a very important public health issue, says 

 a clinician and researcher at Cincinnati Children's Hospital Medical Center, whose work focuses on factors behind changes in puberty and related health risks.

Biro points to other research that has found that around the world, girls have been developing breast buds – usually the earliest sign of puberty – six to 12 months earlier than they used to. Coupled with the dropping age of first menstruation, he says, “in the next decade or two, one would anticipate that there could be a rise in new cases of breast cancer.”

So what’s behind the changing timing of menstruation and puberty?

“When we're looking for causes or explanations, it's not just one thing. It's multiple factors,” Houghton says.

For example, obesity is known to raise the risk of early puberty in girls, and childhood obesity rates have been rising. But Houghton notes that stress is also a known factor, and the two could be intertwined.

“When we have higher stress we get higher cortisol hormones, we get higher androgen hormones,” Hougton explains. “And fat tissue converts those hormones into estrogen. And it's estrogen which signals the body to grow breasts.

Changes in estrogen levels also signal the body to start menstruation.

Endocrine-disrupting chemicals that are widespread in the environment also likely play a role. For example, phthalates – a class of chemicals that are common in many cosmetic and personal care products – are known to interfere with hormones. Some air pollutants are also known to disrupt the endocrine system.

Making sure kids eat a healthy diet — with plenty of fruits and vegetables — can help moderate some of the risk factors for earlier puberty and menstruation, researchers say. Regular physical activity is also important. Getting enough sleep can also help — 

 have linked later bedtimes and shorter sleep duration to earlier puberty.

Mahalingaiah would also like to see parents prepare themselves, and their children, for the fact that menstruation might come sooner than they expected, so when the time comes, they are mentally ready.

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Girls in the U.S. are getting their first menstrual period about 6 months earlier on average than they did in the 1950s and ‘60s. And more girls are beginning menstruation before the age of 9, which is considered a very early age. That’s according to a large new study published this week in the journal JAMA Network Open.


Girls are getting their first periods earlier. Here's what parents should know

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