TUESDAY, Dec. 26, 2017 (HealthDay News) -- A girl who gets her first menstrual period early in life -- possibly as young as 7 -- has a greater risk for developing depression and antisocial behaviors that last at least into her 20s, a new study suggests.
"Girls who go through puberty earlier than peers tend to be more psychologically vulnerable during adolescence," said study lead author Jane Mendle, a clinical psychologist and associate professor of human development at Cornell University.
It hadn't been clear, though, whether that vulnerability extends past the teen years. That's where the current study comes in. Mendle and her colleagues followed a group of almost 8,000 young women into their late 20s.
"Girls who went through earlier puberty are still showing higher rates of depressive symptoms and antisocial behavior than their peers well over a decade past adolescence," Mendle said.
An early first period is a sign of early puberty.
Mendle said there's no consensus on what constitutes an early first period, but girls in the study got their first period at age 12, on average. Some girls had their first period as early as 7 years old, though that was rare: Less than 1 percent of the girls had a first period that young.
However, nearly 7 percent of the girls had their first period at age 10, and 19 percent at age 11, according to the study, published online Dec. 26 in Pediatrics.
The cause of early puberty is generally not known, said Dr. Ellen Selkie, an adolescent medicine specialist with the University of Michigan and author of an editorial accompanying the study. There's also no proven way to prevent early puberty, she said.
Mendle said that other research has suggested that obesity or exposure to endocrine-disrupting chemicals may play a role. Such chemicals are found in plastics and flame retardants, she said.
Whatever the cause of early puberty, the new study found that it appears to have lasting consequences.
"Puberty has repercussions for virtually all domains of life," Mendle said. "Even though it's a biological transition, it's accompanied by dramatic changes in social roles and relationships, emotions and how kids think about themselves and others and their place in the world."
That said, she added that early puberty likely plays only a small role in contributing to depression and antisocial behaviors. And the current study was not designed to prove a direct cause-and-effect relationship.
"Even if a girl goes through earlier puberty, it doesn't mean she will necessarily struggle as an adult in the ways shown in our study," Mendle said. "It's an added risk, and one worth paying attention to. But depression and antisocial behavior are complicated and determined by many different factors, aside from when puberty happens."
Dr. Victor Fornari, director of child and adolescent psychiatry at Zucker Hillside Hospital in Glen Oaks, N.Y., said that antisocial behaviors are those that "deviate from the social norms -- like violating rules, lying, cheating and other not socially appropriate behavior." He was not involved with the study.
So how might early puberty contribute to these types of behaviors and depression?
Selkie said the connections are probably biological and psychological.
"There's some thought that early estrogen exposure might increase the risk for depression, but there are also the factors of being different physically from other kids if you experience puberty at an earlier age," she said.
Carole Filangieri, a clinical neuropsychologist at NYU Winthrop Hospital in Mineola, N.Y., who was also not part of the study, warned against thinking that early puberty might actually cause the behaviors it was linked to in the new research.
"The danger is thinking that early puberty itself is predictive of these antisocial behaviors," she said. "Environments growing up, social pressures growing up as women at a much earlier age and being treated in a more adult-like fashion are all part of the larger picture, and we need to look at what's going on in a girl's life."
As an example, Filangieri said, "for a 9-year-old girl, getting wolf-whistled on the street is confusing and upsetting."
As Fornari said: "This study brings attention to the fact that early menarche isn't just about a girl getting her period. It helps educate parents that they should look for mood and behavior disturbances and get necessary care."
The earlier treatment is started, the better, he said -- no matter what the cause of early puberty might be.
Selkie agreed. "I think the major take-home message for parents about this study is that kids may start developing puberty as early as age 8 or 9, although this is not all children," she said.
"If your child is developing earlier than their peers, it's important to pay close attention to how they are feeling -- from a mood and behavior standpoint -- so that if interventions are needed, such as psychotherapy or medications, we can get those started and hopefully prevent further problems in the future," Selkie said.
The American Psychological Association has more on .