PUBERTY TOO SOON
The 8-year-old polishes off lunch (leftovers microwaved in a plastic bowl), refills her water bottle from the tap and grabs a stack of compact discs before heading to a friend’s house.
It’s the kind of thing kids do every day, without realizing they’re being exposed to chemicals that could trigger puberty to start too early.
Scientists agree sexual development is beginning earlier and earlier in American girls. That can leave girls with well-developed bodies they’re not emotionally equipped to handle. It also increases the risk of breast cancer later on.
What’s less certain is why it happens. A link between obesity and early puberty is clear, researchers say. But many of the 40 doctors and scientists who met last month in Chicago to review research on early puberty suspect something else is at play.
They’re taking a closer look at chemicals that mimic hormones and are found in pesticides, cosmetics and in a vast array of plastic items from CDs to water bottles to food containers commonly used to store or microwave food.
The chemicals are called endocrine disrupters because they’re thought by some scientists to disrupt the hormones and glands that control the reproductive system, said Theo Colborn, a former senior scientist at the World Wildlife Fund who wrote a book on the topic. If parents could minimize exposure, it might give them hope of delaying puberty and thus reducing the risk of cancer.
Yet, well before an infant uses her first plastic teether or baby bottle, Colborn said, she’s already been exposed.
Thanks to their mothers’ exposure, even babies in the womb have measurable doses of the hormone-mimicking chemicals, Colborn said.
From birth onward, the chemicals are hard to avoid. Two of the oft-cited culprits, bisphenol-A and phthalates (pronounced thalates), are in common use.
"We have widespread exposure to bisphenol-A. It’s in practically everything. It’s been found in blood throughout the Northern hemisphere," said Colborn, author of a book on endocrine disrupters titled "Our Stolen Future: Are We Threatening Our Own Fertility, Intelligence and Survival? A Scientific Detective Story."
Phthalates are added to plastics to make them more flexible and durable and they, too, are very hard to avoid. Often, we consume them with our food.
Colborn says research is finding that phthalates leach out of plastic food containers and plastic cling wrap into food, and then into our bodies. Heating food in plastics causes a chemical reaction that intensifies the leaching.
Bisphenol-A, meanwhile, is found in the liner of almost every can of food.
Over time, it might be enough to push puberty forward, some researchers argue.
Plastics makers, who’ve conducted their own research, disagree. A weak estrogen-like effect was noticed in the lab, but not when living animals were exposed to the chemicals, said Marian Stanley of the Phthalate Esters Panel of the American Chemistry Council, an industry group.
There’s little doubt that girls are growing up earlier. A landmark 1997 study of 17,000 girls startled parents with its findings that nearly 7 percent of white girls and 27 percent of black girls start developing breasts by age 7 – during second grade.
The study also found the average age was younger than parents probably expected. White girls now start breast development at an average age of 10 years and black girls at 8.9 years. (While some researchers hypothesize boys also might be going through puberty earlier, research has only begun.)
On average, black and white girls start to menstruate, called menarche, during their 12th years – about four months earlier than their moms, one study said. A second study found menstruation began three months earlier. Both studies were reported in the journal Pediatrics.
That amounts to shaving one month every decade off the average age of menarche, researchers in the second study pointed out.
"If you extrapolate over a century, menarche would be nearly a year earlier," said Marcia Herman-Giddens, a public health professor at the University of North Carolina.
Can’t ignore it
Could exposure to endocrine disrupters contribute to such a change?
Most of what science knows about the chemicals comes from animal research. The U.S. Environmental Protection Agency says "compelling evidence" shows endocrine disrupters have impaired the reproductive systems of fish and wildlife. That includes changes to puberty.
Herman-Giddens cited a Michigan case in which girls and women were affected when an endocrine disrupter chemical accidentally got into cattle feed.
A study of pregnant women who ate the beef from those cattle, then gave birth to baby girls, found that, years later, the girls started menstruating a full year earlier than girls in a control group.
"That’s pretty remarkable," Herman-Giddens said.
Similarly, a study of girls in Puerto Rico who were developing breasts at very young ages found elevated levels of phthalates in their blood, she says.
Science knows relatively little about human experience with endocrine disrupters. Because of the lack of human data, scientists debate how much of a risk exists.
Colborn believes the risk from plastics is greater than the risk from hormones in meat, milk and eggs that come from growth stimulators given to animals. Still, she advises buying hormone-free foods.
Parents ought to hedge their bets and shield children from chemicals in plastics, fragrances, cosmetics and air fresheners – to the extent that’s possible, Herman-Giddens said.
"Since these substances are known to disrupt in animals, it’s hard to imagine they wouldn’t in humans," she said.
The fat factor
Researchers clearly have shown a link between obesity and early puberty for girls.
"On average, girls’ overweight will trigger puberty. Maybe not for every girl, but on average, yes," said Herman-Giddens, who led the 1997 puberty study of 17,000 girls.
Obesity and puberty have a complex relationship
"If you’re a chubby girl, you look like you have some breast tissue, and you may, because fat makes estrogen," says Dr. Edward Reiter, a pediatric endocrinologist at Baystate Medical Center Children’s Hospital in Springfield, Mass.
But obesity doesn’t let environmental toxins off the hook as a possible cause for early puberty.
Reiter points out that toxins our bodies absorb from the environment get stored in fat. Thinner people might not store as many toxins, and thus might reach puberty later.
While many researchers worry about puberty’s early onset, others take comfort in the fact that the span from the first signs of puberty to menarche remains steady at about 2 years.
"The tempo of puberty is really important," says Dr. Mel Grumbach, who teaches pediatrics at the medical school of the University of California, San Francisco. "The (age of) onset may be changed, but the tempo has not been accelerated."
Reiter said he probably would not intervene medically for a 7-year-old girl who showed slight breast development but no other signs of puberty.
If the girl progressed quickly to other signs of puberty, however, he probably would recommend a drug, Lupron, to halt it. Besides a young girl’s discomfort with having breasts and menstrual periods, there’s also a danger her growth spurt might come too soon, leaving her a very short adult.
How it affects kids
The greatest danger of early puberty is that it raises the risk young girls might get breast cancer later in life. Numerous studies clearly show the link.
"If you have a longer exposure to estrogen, the higher the chance you’ll develop breast cancer," says Herman-Giddens.
Besides that serious medical risk, early puberty can cause girls emotional and social distress or discomfort. If a girl is developing breasts, she looks older than her age, and other children and adults generally treat her so. Yet she still has a child’s mind and interests. She probably won’t grasp the implications of appearing sexually mature.
"Older boys and men are hitting on them, and they have no way of dealing with it," said Herman-Giddens.
There’s really no benefit for girls in developing earlier. Studies show girls whose bodies mature earlier are at greater risk for earlier sexual activity. Because they might hang out with older kids who look more like them, they also are at increased risk for drug and alcohol use.
"If a young kid is having breast development, you have to ask, ‘Is she emotionally capable? Is she at risk for abuse? Is she at risk for earlier sexual activity? All these behavioral matters are worth thinking about," Reiter said.
For Herman-Giddens, such questions reinforce her belief that early puberty is something public health experts, as well as parents, ought to worry about.
"This is a serious public health issue," she said. "It’s the canary in the coal mine."