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Is puberty before 10 the new normal for U.S. girls?

A 2010 study found that girls — particularly white girls — were more likely to begin developing breasts at age 7 or 8 than they were in the 1990s.

Katie Couric interviewed New York Times Magazine contributor Elizabeth Weil on "Good Morning America" about her article on early puberty for girls.

As I noted Monday, bisphenol A (BPA), the chemical that the Food and Drug Administration has decided not to ban in food packaging (at least for now), has been cited by some scientists as a possible cause of early puberty in girls.

I thought of that possible connection as I read Elizabeth Weil’s article in the New York Times last weekend, which asked a provocative question that’s on the minds of a lot of parents with young daughters: Is puberty before age 10 now the new normal in the United States?

As Weil points out, most researchers now seem to agree that “breast budding,” the initial growth of breasts, is starting earlier today than it did in past generations. A 2010 study published in the journal Pediatrics found that girls — particularly white girls — were more likely to begin developing breasts at age 7 or 8 than they were in the 1990s. A similar trend has been found among Danish girls.

But what those findings mean is not clear, writes Weil, particularly since research has also shown that the average age of first period (menarche) hasn’t changed that much, dropping only to 12.5 from 12.8 years.

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In other words, girls appear to be developing breasts at a significantly earlier age than in past generations — even very recent generations — but they’re not starting menstruating much earlier. (The 1,200 girls in the 2010 Pediatrics study are being followed for five additional years to see if they also begin menstruating at an earlier age than previous generations.)

Some researchers believe breast budding is not necessarily a sign of early puberty. As one researcher explained to Weil, true puberty starts in the brain, with the production of gonadotropin-releasing hormone (GnRH), which then signals the ovaries to start making estrogen and breasts to form.

Breast development can also occur, however, when estrogen comes from other sources — ones that originate outside the brain.

And, indeed, the Danish girls with early breast development were found to have surprisingly low levels of naturally occurring estrogen in their bodies.

The main suspects

Which brings us back to BPA. Writes Weil:

Animal studies show that the exposure to some environmental chemicals can cause bodies to mature early. Of particular concern are endocrine-disrupters, like “xeno-estrogens” or estrogen mimics. These compounds behave like steroid hormones and can alter puberty timing. For obvious ethical reasons, scientists cannot perform controlled studies proving the direct impact of these chemicals on children, so researchers instead look for so-called “natural experiments,” one of which occurred in 1973 in Michigan, when cattle were accidentally fed grain contaminated with an estrogen-mimicking chemical, the flame retardant PBB. The daughters born to the pregnant women who ate the PBB-laced meat and drank the PBB-laced milk started menstruating significantly earlier than their peers.

One concern, among parents and researchers, is the effect of simultaneous exposures to many estrogen-mimics, including the compound BPA, which is ubiquitous. Ninety-three percent of Americans have traces of BPA in their bodies. BPA was first made in 1891 and used as a synthetic estrogen in the 1930s. In the 1950s commercial manufacturers started putting BPA in hard plastics. Since then BPA has been found in many common products, including dental sealants and cash-register receipts. More than a million pounds of the substance are released into the environment each year.

But endocrine-disrupting chemicals are not the only suspects behind early breast budding and puberty. Writes Weil:

Girls who are overweight are more likely to enter puberty early than thinner girls, and the ties between obesity and puberty start at a very young age. As Emily Walvoord of the Indiana University School of Medicine points out in her paper “The Timing of Puberty: Is It Changing? Does It Matter?” body-mass index and pubertal timing are associated at age 5, age 3, even age 9 months. This fact has shifted pediatric endocrinologists away from what used to be known as the critical-weight theory of puberty — the idea that once a girl’s body reaches a certain mass, puberty inevitably starts — to a critical-fat theory of puberty. Researchers now believe that fat tissue, not poundage, sets off a feedback loop that can cause a body to mature. As Robert Lustig, a professor of clinical pediatrics at the University of California, San Francisco’s Benioff Children’s Hospital, explains, fatter girls have higher levels of the hormone leptin, which can lead to early puberty, which leads to higher estrogen levels, which leads to greater insulin resistance, causing girls to have yet more fat tissue, more leptin and more estrogen, the cycle feeding on itself, until their bodies physically mature.

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A serious concern

Weil explains in her article why early puberty should concern parents — and the rest of us. “We know that girls who develop ahead of their peers tend to have lower self-esteem, more depression and more eating disorders,” she writes. “They start drinking and lose their virginity sooner. They have more sexual partners and more sexually transmitted diseases.”

Early menarche is also associated with a higher risk of type 2 diabetes and breast cancer in adulthood.

The parents Weil interviewed for her article have made all sorts of desperate attempts to slow down their daughters’ progression through an early puberty. “Some trained with them for 5K runs (exercise is one of the few interventions known to help prevent early puberty); others trimmed milk and meat containing hormones from their daughters’ diets; some purged from their homes plastics, pesticides and soy,” Weil reports.

But, as ecologist and author Sandra Steingraber (“Raising Elijah: Protecting Our Children in an Age of Environmental Crisis”) told Weil, “This idea that we, as parents, should be scrutinizing labels and vetting birthday party goody bags — the idea that all of us in our homes should be acting as our own Environmental Protection Agencies and Departments of Interior — is just nuts. Even if we could read every label and scrutinize every product, our kids are in schools and running in and out of other people’s homes where there are brominated flame retardants on the furniture and pesticides used in the backyard.”

And BPA in our food packaging.

You can read Weil’s article on the New York Times website. (Warning: If you’re not a subscriber, clicking on the link will count toward your monthly 10 free articles.) You can also watch Weil and Dr. Jennifer Ashton discuss the article on “Good Morning America.”

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