Since the 1996 publication of Theo Colburn’s seminal Our Stolen Future, scientific research into the possible causes of early puberty has increased dramatically. And with good reason—early puberty has a strong association with increased rates of breast cancer, the second leading cause of cancer deaths among American women. Today puberty is occurring one to two years earlier for U.S. girls than it did 30 years ago. Breast development is now considered “abnormal” at age seven for white girls and age six for African-American girls.
In a 2007 report for the Breast Cancer Fund, “The Falling Age of Puberty in U.S. Girls: What We Know, What We Need to Know,” ecologist Dr. Sandra Steingraber outlines the most plausible reasons for early puberty, from increased obesity rates and exposure to toxic pollutants to excessive television watching.
Increased screen time over the last 30 years has meant an increasingly sedentary lifestyle for kids, a major cause of obesity. Preliminary data from a Italian study on melatonin production showed that children ages six to 13 denied access to TV and computer screens for one week produced 30 percent more melatonin. Children before puberty produce more melatonin than those after.
“Melatonin is the body’s internal clock, as well as its internal calendar,” says Steingraber. “It’s an inhibitory signal for puberty so the more melatonin you have, the later you go into puberty.”
According to the National Health and Nutrition Examination Survey (NHANES), 17.5 percent of children ages six to 11 were overweight between 2001 and 2004—an effective doubling of obesity in the past 30 years. According to the Obesity Society, one in five U.S. children is overweight. And percentages are higher for populations of Hispanic, African-American and Native American children. Chubbier children enter puberty earlier and those who demonstrate precocious puberty are more likely to become obese in adulthood. One factor may be a protein called leptin, which comes from fat cells and is linked to early breast development.
Some obesity cases may have environmental roots. Organotins, chemical compounds found in disinfectants, outdoor paints and epoxyresins, are thought to have the ability to disrupt endocrine systems, another potential early puberty culprit.
Obesity is clearly not the only cause. Comparing girls with the same body mass index in Denmark and the U.S., Danish girls hit puberty a full year later than their American counterparts. Similarly, wealthy girls in South Africa don’t reach puberty until a full year after African-American girls. Many researchers are studying the relationship between chemical pollutants like PCBs (polychlorinated bphenyls) and phthalates (commonly used plasticizers) and premature development. One 20-year study showed that the more PCBs a girl was exposed to before birth, the greater the likelihood of both obesity and early puberty. In Puerto Rico, where girls as young as two have been developing breasts, researchers found that soy formulas were partially to blame, as were the phthalates in nail polish, food packaging and other common items.
“Companies that make consumer products do a good job of keeping a veil of secrecy around their products,” says Steingraber. “We don’t even know the pathways of these exposures. It may not be so much what the child is exposed to but what the mother was exposed to while pregnant.”
Last year, the National Institute of Environmental Health Sciences honored Dr. Heather Patisaul of North Carolina State University for her work on the relationship between low-dose exposures to Bisphenol-A (BPA, a synthetic compound found in plastics and epoxyresins like dental sealants and the seals on soup cans) and exposures to Genistein (a naturally occurring compound in soy products) and precocious puberty.
“We are seeing earlier puberty with both of these compounds when animals are exposed to them,” says Patisaul. “In humans and animals it by and large affects girls more than boys, 10 to one.” A recent paper in the journal Reproductive Toxicology suggests that a federal panel caved to industry pressure in promoting the safety of BPA, which has been linked to cancer, obesity and diabetes. Other researchers have found links to premature sexual development after exposures to flame retardants called polybrominated biphenyls (PBBs), dioxin pollutants and accidentally ingested pharmaceuticals.
“In no way do we think there is one single thing driving early puberty,” says Patisaul. “We’re becoming more concerned because we’re putting more soy in our diet.” Processed soy is found in milk, cheese, tofurkey and formula milk.
Unlike in Asia, where traditional diets rely on whole soybeans, U.S. soy is broken down into component parts. Compounds called isoflavones in soy can act like estrogen in the body, stimulating female characteristics. “In the west, we put our kids on soy infant formula and they are exposed to massive amounts of these compounds,” says Patisaul.
Additionally, early puberty raises the stakes for girls before breast cancer is a real threat. Girls who come to puberty earlier have higher rates of drug abuse, violence, unintended pregnancies, more problems in school and mental health issues.
“Teachers respond to early maturing boys as leaders. Their academic levels go up,” explains Dr. Steingraber. “But early maturing girls are treated as sexual objects. Shortening childhood means a shortening of the time before the brain’s complete resculpting occurs. Once that happens, the brain doesn’t allow for complex learning.”
Before the presence of sex hormones, the brain can build the connections used to learn a language, play a musical instrument or ride a bike. The sort of healthy explorations children need before the adult world comes knocking.