Puberty typically isn't a favorite memory for any of us. During that angst-ridden ride between childhood and adulthood, nearly everyone's best goal is simply to fit in. That's even tougher when you're only in second grade.
But a significant percentage of girls begin breast development — an indicator of puberty — before learning their multiplication tables. According to several headline-grabbing studies, both here and in Europe, a dramatically greater number of girls start to develop breasts at a younger age than happened 10 to 30 years ago. By contrast, the age at which they get their first periods has only declined by a few months and, on average, still occurs, between the ages of 12 and 13.
These findings, though still debated by some endocrinologists, have fueled concern that childhood for girls is shrinking, while the duration of puberty is expanding.
The Elusive Why
Exactly why this may be occurring still is clinically elusive. Several possibilities have been identified, including an increase in obesity, low birth weight, stress and the prevalence of estrogen-like hormone-disrupting chemicals, such as bisphenol A, or BPA. BPA is used in hard plastics and in July was banned for use in baby bottles and sippy cups by the Food and Drug Administration.
Research also has turned up an intriguing list of sociological associations, such as having an absentee father.
Before delving deeper, let's first take a quick trip back to junior high health class for a refresher on how puberty occurs. In girls, it usually begins between ages 8 and 13 and is triggered when an area of the brain called the hypothalamus secretes gonadotropin-releasing hormone (GnRH). This kicks off a hormonal chain reaction that causes the pituitary gland to secrete two hormones (called gonadotropins) that stimulate the ovaries to produce estrogen. As a result, secondary sex characteristics develop and the body becomes capable of reproduction.
Breast development is usually the first sign, followed by the appearance of pubic hair and then menstruation (menarche), which generally occurs within two to three years.
For a small percentage of girls, precocious puberty is caused by a diagnosable disorder, such as a genetic condition or brain tumor. In these cases, the main health risk is a stunting of bone growth. If a growth spurt starts early, a girl initially may be taller than her peers. But, because her bones often stop growing earlier than usual, she can end up shorter than average as an adult.
Depending on the underlying condition and its progression, early puberty may be treated with a medication, such as leuprolide, which delays further development. Once the medication is stopped, the puberty process restarts.
Early puberty, particularly getting an early first period, also may be a risk factor for getting breast cancer later in life because the window of exposure to estrogen is wider.
Looking like a woman when you're still a little girl can cause social and emotional difficulties, too. That's the case regardless whether a 7-year-old is budding breasts because of a known medical condition or is merely an early bloomer.
The first major report suggesting a decline in the age of puberty created controversy back in 1997. After studying 17,000 girls, researchers concluded that among white girls, the average age of breast budding was 9.96, while it was 8.87 for African-American girls. Until then, the generally accepted age was 11 or so. (For unknown reasons, studies consistently have found that, on average, African-American girls develop earlier than white girls.)
Then in 2010, another major study corroborated the trend. Trained examiners evaluated breast development of more than 1,200 girls between ages 6 and 8 in the San Francisco area, Cincinnati and East Harlem.
Across the three sites, examiners reported a dramatic increase of 7-year-olds who had begun developing breasts. The increase was greatest among whites, though, on average, African-American girls, followed by Hispanic girls, develop earliest. At age 7, 10.4 percent of white, 23.4 percent of black and 14.9 percent of Hispanic girls had enough breast development to be considered at the onset of puberty. At age 8, the figures were 18.3 percent in whites, 42.9 percent in blacks and 30.9 percent in Hispanics.
Scandinavian researchers noted the same trend in a 2006 study. Their research, involving more than 1,000 girls in Copenhagen, Denmark, concluded that mean age for breast budding in that country had declined to 9.86 years from 10.88 years as recorded 15 years earlier.
What's going on?
One factor most endocrinologists, including this one, can agree on is that heavier girls tend to develop earlier than thinner ones possibly because they have higher levels of the hormone leptin, which together with other signals may stimulate the onset of puberty. Fat tissue itself is active endocrinologically. It can take hormones from the adrenal glands and ovaries and convert them into estrogens, which brings about breast development, enlargement of the uterus and the growth spurt that is characteristic of puberty.
The link between weight and puberty appears to begin early, too. A University of Michigan study, which followed 354 girls from their 3rd birthdays through sixth grade, found that higher body fat at age 3 was associated with earlier breast development. Rate of change also was important: the faster that body fat increased between ages 3 and 6, the greater the chances that breast-budding would begin by age 9.
The fat connection may even begin in the womb. Researchers fed pregnant rats a high-fat diet throughout pregnancy and lactation (breastfeeding). Control animals ate regular rat chow. After weaning from their mother's milk, the offspring ate either regular chow or a high-fat diet. The onset of puberty was much earlier in all rats whose mothers had a high-fat diet, compared with the control group eating a regular diet.
Meantime, research also suggests a link between early puberty and low birth weight that is followed by nutritional rehabilitation. That recovery, in turn, leads to catch-up growth. It, in turn, can cause an increase in secretion of pituitary hormones, which can trigger puberty. This phenomenon has been observed among malnourished babies adopted from poor countries to more prosperous ones. In the United States, the number of low birth weight babies increased between 1980 and 2006 and since has held steady at a high rate of about 8.2 percent of births.
Another possible cause may be the exposure to certain environmental chemicals called endocrine-disrupters. Among the most prevalent of these is BPA, which commercial manufacturers have used in hard plastics since the 1950s and most of us have traces of in our bodies. Substantial data links these chemicals to early sexual development in animals but little research has been conducted into the effect on humans.
Several studies also have shown an association between family stress and the timing of puberty. Girls who from an early age have grown up without the presence of their biological fathers, for example, are more apt to begin puberty younger than those who grow up with both parents. The presence of a stepfather in the house or a mother who is depressed also has been linked to developing early.
While early stress may be a cause of premature puberty, the converse is also true. Such stress can put girls at risk for social problems, such as early sexual activity, substance abuse, depression and eating disorders. Girls who look older than their peers can feel self-conscious. They also may attract the attention of older males but are less psychologically mature to resist the negative attention.
What's a mother or father to do? Buy up baggy sweat suits? Bolt the door? Fortunately, there may be a better answer.
According to a study of 330 early developing fifth graders, three distinct positive parenting practices may ease or prevent problem behavior among early bloomers. These are: Nurture, open communication and knowledge of your child's activities. Parental nurture, generally considered a key factor in curbing risk-taking, may be even more important for early-maturing girls. The thinking is that parental influence can help decrease these youngsters' susceptibility to peer influence, assist them in developing better coping skills and diffuse negative feelings that might turn into negative thoughts and actions.
So, moms and dads and uncles and aunts and teachers and all you other grown-ups: Whether it arrives early, with some special challenges, or at its more expected time, puberty's always a challenge for girls and boys. And it's up to us to assist them in growing up, whenever nature determines, to be the finest women and men possible.