“Now studies show 25 percent of African American girls have breast development at age 7. Fifteen percent of Hispanic girls and 10 percent of Caucasian girls show breast development by that age. Even that 10 percent number is dramatically higher than it was a few decades ago.”
When these processes begin at an earlier age, it can be more than socially awkward. Early puberty carries risks for girls' psychological and physical health, sometimes long after they have grown into adult women. Parents can help mitigate the chances of their children going through early puberty, and they can prevent many of its negative consequences if it does happen, say Deardorff and her colleague Louise Greenspan at the University of California, San Francisco. The pair recently collaborated on a book, The New Puberty, that examines the evidence and offers advice for parents. We asked Deardorff to give us some of the highlights:
How Do We Know Girls Are Entering Puberty Earlier?
“During the 1980s and 1990s, [University of North Carolina physician] Marcia Herman-Giddens noticed a phenomenon where a large number of girls coming into her clinic seemed to be developing earlier, some with breast development or pubic hair as young as age 5,” Deardorff says. In 1997, Herman-Giddens published a study in the journal Pediatrics suggesting that girls were beginning puberty earlier. Her research concluded that during the 1860s, girls had their first period around age 16. The age had reached 14 by 1920, Herman-Giddens found, and by 1997 had dropped to around 12 and a half. “That study ignited a maelstrom of controversy.” But other researchers have since added their own evidence, including a major 2010 Pediatrics study co-authored by Greenspan that revealed the early breast development rates cited above.
“Low and behold, it not only corroborated what Marcia Herman-Giddens had found in the 1990s, but it also showed that it was even a bit earlier," Deardorff says. "So I think it's pretty universally accepted now that breast development and pubic hair growth are starting earlier. But first menstruation doesn't seem to be accelerating at the same rate. Today girls get their period only about six months earlier than they did 40 years ago, but they are beginning to get their breasts two years earlier. So that has us really interested in why we would we be starting the process earlier, but not necessarily reaching menstruation earlier. We suspect that puberty is becoming a longer process, that the tempo of the first part of it might be slowing down."
Why Might This Be Happening?
“The evolution of this wouldn't be moving so quickly unless there was some environmental factor or factors prodding it," Deardorff says. Right now, doctors have three main suspects:
- Obesity: As of 2012, a staggering one in 5 U.S. children or adolescents are obese, according to the U.S. Centers for Disease Control and Prevention. Over the last 30 years, the percentage of U.S. children classified as obese has nearly tripled, and the timing of this obesity explosion parallels the rise in early puberty.
“We've known for a long time that you have to have a critical body weight in order to attain puberty," Deardorff says. "In ballerinas, gymnasts, people in times of famine, we see that puberty, and particularly menstruation, can be put on hold because the body just doesn't have enough resources to meet the demands of reproduction. But it's becoming increasingly clear that body weight doesn't just represent some kind of a minimum threshold. The more body fat a girl has, the earlier they go through puberty.”
Some studies have shown that body weight, even as early as age 3, can predict a girl's chances of early puberty. One key link is a hormone known as leptin, which is produced by fat cells. In the brain, leptin reduces hunger and curbs appetite. Obese people usually produce more leptin than others, although their bodies don't respond to it as efficiently. Leptin levels also spike before puberty begins, so bodies with more fat cells can prompt puberty to begin earlier.
- Exposure to Hormone-Mimicking Chemicals: Girls' exposure to an array of potential chemical influences can begin in the womb, so that by the time an 8- or 9-year-old girl begins to undergo puberty, it's difficult to determine which, if any, of the many unintended substances found in her body may have helped trigger the change.
Some endocrine-disrupting chemicals are undergoing specific tests for possible roles in early puberty. These chemicals are so structurally similar to estrogen that, when ingested, they cause estrogen-specific reactions throughout the body. They're found in antibiotics (and in the meat of antibiotic-fed animals), plastics, pesticides and other artificial substances. Natural products like lavender and tea tree oil can also mimic estrogen's effects on the body. Sorting out all the possible impacts of these substances is a confounding puzzle, further complicated by the hurdles involved in conducting tests on human children.
“The research is really in its infancy. Animal studies show that certain chemicals act as endocrine disruptors in the body, certain chemicals can mimic estrogen in the body, which is at the core of the female's reproductive biology. But research to date certainly hasn’t found any smoking guns. We just don't know at what dose or what point in a person's development a certain chemical might or might not have those effects. It is very complicated formula to learn how they might impact the body of a growing girl.”
- Social and Psychological Stress: While stress may not be as strong of a driver compared to the other possibilities, research is suggesting that the body can launch a hormonal response to situations of danger or uncertainly, and it may work in synergy with the other two factors.
“The home environment early in life … does have an impact on the timing of puberty. A family context that's unpredictable, inconsistent or unsafe, or a home with high levels of conflict and low levels of family warmth, these things have been shown to predict earlier puberty. That period of life from birth to 5 years of age, when a girl is probably the most plastic or malleable, is probably the key," says Deardorff.
She adds that there is a huge social disparity involved in the onset of early puberty. This, more than the underlying genetics of any particular ethnicity, probably has more to do with why early puberty is so much more common among African American and Latino populations in the United States. “When you have 25 percent of African American girls entering puberty by age 7, versus 10 percent of Caucasian girls, there is an issue here. When you are talking about obesity, and exposure to poor environmental circumstances, and psycho-social stresses, we know that these things are more prevalent in communities that are struggling.”
“It's associated with a higher risk for depression, anxiety, body image issues and eating disorders. Also, [early puberty is linked to] the early onset of sexual activity and substance use, especially alcohol. And when girls start to initiate these problem behaviors earlier, like alcohol use for example, they are at much higher risk for problems later.”
Early onset of puberty may also play a role in later life, Deardorff says. Early pubic hair growth in overweight girls may be due to insulin resistance and has been linked to increased risk of metabolic disorders, including obesity, heart disease and diabetes. “Early menstruation has been shown in multiple studies to put girls at some higher risk later in life for breast cancer. There has also been evidence for increased risk of cardiovascular problems. There have even been a few studies showing that early menstruation leads to earlier all-cause mortality.” Deardorff adds that we know very little about the potential advantages that early puberty may provide because any potential benefits have been understudied.
What Can Parents Do?
In terms of preventing early puberty, parents might limit chemical exposures just as they would for a host of other health reasons, Deardorff says. Organizations like The Environmental Working Group produce consumer guides to toxic ingredients in foods, personal care products, cleaning supplies and more.
“Try to operate under the precautionary principle. Don't microwave food in plastic, store things in glass, try to use some protective wear instead of sunscreen if you can, don't smoke or expose your kids to second-hand smoke. There is some low-hanging fruit here, in terms of things you can do to reduce risks.” Perhaps the most important thing parents can do, however, is focus on the home and family environment and be there for their daughters.
“It appears that a really strong, safe family context seems to mitigate all or most of early puberty's short-term risks for adolescents. That's of immense importance for girls who are in early development. It's most important to build emotional closeness early. Don't start at age 14. Pay attention to your kids. Take some time out from your busy lives and devices and build that emotional bond that is so important to them.”
source: smithsonian.com By Brian Handwerk