Goodbye, girls

Researcher ponders why U.S. kids reach puberty at an ever-younger age

By Chris Lydgate

Pamplin Media Group, May 15, 2008, Updated Oct 30, 2009

COURTESY OF SANDRA STEINGRABER

Sandra Steingraber says obesity, premature birth or exposure to chemicals may contribute to the earlier onset of puberty in girls.

If historical statistics are any guide, the average girl in northern Europe in the 1830s entered puberty — defined by menarche, or the onset of menstruation — at approximately 17 years of age. Today, chances are that her American counterpart will have her first period at about 12 and a half.

Other signs of sexual maturity also are appearing sooner. Half of all girls in the U.S. show breast development by their 10th birthday, 14 percent by the time they’re 9.

The acceleration is so pronounced that in 1999 American pediatricians redefined the threshold of “normal,” scaling it back to 8 for white girls and 7 for black girls (who tend to reach puberty significantly earlier.)

This relentless erosion of girlhood — echoed across the more affluent nations of the world — is tripping alarm bells for researchers, environmentalists and parents.

First, girls who hit puberty sooner are more likely to wind up with a long list of health and social problems.

Second, it raises the unpleasant possibility that something sinister in our environment may be sabotaging the complex hormonal system that governs sexual development.

Biologist and author Sandra Steingraber, an interdisciplinary scholar at Ithaca College in upstate New York, spent a year reviewing the scientific literature on the subject.

According to Steingraber, the main forces driving the acceleration of puberty are obesity and premature birth. But she remains convinced that environmental exposure to chemicals, particularly endocrine disruptors, also may play a significant role.

Steingraber, whose report, “The Falling Age of Puberty in U.S. Girls,” was published last year by the Breast Cancer Fund, will be discussing her research this month at a lecture sponsored by the Oregon Environmental Council.

At-risk behavior increases

Early puberty has received a lot of attention from medical researchers because it has been identified as a risk factor for breast cancer. But as she delved into the subject, Steingraber found that girls who enter puberty early also are more likely to smoke, drink, abuse drugs, and have sex at a younger age.

“Almost everything bad that could happen to a teenage girl happens more often, and more intensely, to girls who enter puberty prematurely,” she said. “Basically, the modern world is not a good place to be an early-maturing girl.”

All of which is somewhat surprising because, biologically speaking, early puberty could be considered an auspicious omen. In fact, the timing of sexual maturity among most mammal species is elastic, and tends to be delayed by disease, malnutrition and stress.

From an evolutionary standpoint, this makes sense: There’s not much point in an organism gearing up for fertility, with its mischievous handmaidens, mating, pregnancy and birth, if the environmental outlook is grim.

Thus early puberty implies that a girl is thriving. Indeed, the most dramatic advance in the age of menarche seems to have taken place before 1970, a change Steingraber and most other researchers attribute to better nutrition and less disease.

But while the march of menarche has slowed (it now creeps forward at the rate of roughly two months per decade), the other signs of sexual maturity continue to arrive fast and furious.

White girls in America now begin breast development, on average, a full year earlier than was reported in 1969; black girls, a full two years earlier.

“There is definitely a trend toward earlier puberty,” says Dr. Bruce Boston, a pediatric endocrinologist at Oregon Health and Science University.

This perplexing phenomenon has led many researchers to suggest that other factors are at work, including chemical exposure, growth hormones in milk or meat, formula feeding, absent fathers, and even the pervasive sexual imagery in American culture.

Theories run the gamut

In her study, Steingraber methodically sifts through the evidence for each theory. Some are easy to dismiss. Sure, teenage girls on the prairie couldn’t sit back and watch “Sex and the City,” but there is no evidence that sexual imagery awakens puberty, and no hormonal mechanism for it, either.

Blaming derelict dads may sound outlandish, but it does have a scientific basis: Absence of the biological father is associated with early puberty in several mammal species.

However, it is not clear that fathers are statistically absent more often today than in the past: War and disease orphaned many girls in the 19th century, not to mention long periods of separation demanded by farming, hunting, fishing and so on.

Perhaps more surprising, Steingraber finds little reason to pin the blame on growth hormones in milk.

The American dairy industry began using recombinant bovine growth hormone (rBGH) to boost milk production in 1993 (though virtually all Oregon dairies shun it) but puberty has been advancing long before that.

In addition, American children typically drink less milk than they did in ages past.

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