Health & Science

Younger Girls, Bigger Breasts: Are Chemicals to Blame?

Surprising new research on early puberty.

We’ve all heard the stories and seen the evidence: Girls are getting breasts a lot earlier than we remember from our own elementary school days. Nobody really knows why. But because girls are also getting chubbier (along with the rest of the population), that’s been the favored theory of causation. Here’s the general evolutionary scenario: If you can eat more, you can reproduce earlier. And in fact, thanks to better nutrition and less disease, the average age of sexual maturity in girls has dropped slowly but steadily, about three months per decade, since 1850.

In 1997, though, Marcia Herman-Giddens, a scientist at the University of North Carolina, noticed that the pace of advancing puberty had greatly, unexpectedly, accelerated. And that’s no longer a good or neutral thing, because girls who enter puberty on the early end of the spectrum are at greater risk for breast cancer later on. They also tend to suffer more psychological and behavioral problems such as depression and substance abuse.

In a bombshell of a paper, Herman-Giddens wrote that girls were developing breasts, sprouting pubic hair, and getting their periods one to two years younger than previously thought, with white girls getting breasts at a mean age of 9.8 and black girls at 8.8 (menstruation typically starts two to three years later). The data were controversial: European scientists weren’t finding similar changes, and the breast observations were considered subjective—how did researchers know what was a budding breast and what was a little extra fat? To the extent the paper was credited as telling a true story, the cause was again chalked up to body weight: During the last 30 years, the percentage of American girls between the ages of six and 11 who are obese has more than tripled, to 16 percent. Fat stores estrogen and triggers leptin, another hormone involved in the puberty sweepstakes. So far so clear.

But a new study out of Denmark, published last month in Pediatrics, shows that the link between early puberty and fat isn’t the whole story. And, note from Hamlet: We ignore strange things in the state of Denmark at our peril.

For starters, the new paper confirms the American findings almost exactly. Girls are getting breasts earlier, and it’s happening fast. Researchers used the exact same protocols to measure almost 1,000 girls in Copenhagen in 1991 and a second group of the same age in 2006. The girls—all white and middle class—started budding breasts a full year earlier than their counterparts just 15 years ago (the age of menstruation had advanced about four months). While that’s a stunner in itself, the real head-scratcher was that the change in girls’ body weight was minimal and couldn’t account for the difference. Nearly all the girls in both groups were relatively thin, says Dr. Lise Askglaede, the study’s principal author at the University of Copenhagen.

So if fat isn’t resetting the puberty clock, what is?

Two other leading theories have been divorce and the media. It’s been documented that girls not living with a biological father tend to mature earlier, just like elephants, believe it or not. But if anything, families are slightly more stable now than they were 20 years ago. And if girls are becoming more sexualized from the constant stream of media images, their hormone levels would also be rising, and, notably, that’s not happening. While the Copenhagen girls are growing breasts earlier (which requires estrogen), their bodies are not making any more estrogen than the first group of girls were in 1991. To Asklaede, this indicates that the estrogen must be coming from somewhere else.

“Our best suggestion is that it is something from outside,” Aksglaede says. “The main discussion is environmental factors.” Specifically, chemicals that mimic hormones, many of which girls are exposed to every day. Called endocrine disrupting compounds, or EDCs, these chemicals include the much publicized baby-bottle ingredient, BPA, as well as pesticides, compounds in cigarettes, and phthalates (a family of molecules used as aroma stabilizers in lotions and shampoos as well as a common additive in household plastics), among many others. The U.S. government does not currently test chemicals for their effects on human hormonal systems, and the European Union is only just starting to do so.

Tags: early puberty, lise askglaede, marcia herman-giddens

Florence Williams is a contributing editor to Outside Magazine and also writes for the New York Times Magazine, the New Republic, and other publications. Last year she was a Ted Scripps Fellow at the Center of Environmental Journalism at the University of Colorado.

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