As more girls hit puberty at younger ages, scientists search for environmental links

Frank Biro, MD, says our obesity problems might be more than just poor lifestyle choices.

Frank Biro, MD, delves into the connections between puberty, obesity and our environment.Frank Biro, MD, delves into the connections between puberty, obesity and our environment.

The “dirty dozen”

To help avoid chemicals that may be getting into his food, Frank Biro, MD, director of adolescent medicine at Cincinnati Children’s, makes a point of eating organic, particularly when it comes to the “dirty dozen.” That’s the list of foods the Environmental Working Group, a nonprofit dedicated to uncovering environmental health threats, says have the highest levels of pesticides and other obesogens. If you are unable to buy organic, thoroughly washing fruits and vegetables can reduce pesticide exposure.

The "dirty dozen" are:

Imported nectarines
Imported grapes
Sweet bell peppers
Domestic blueberries
Kale/collard greens 

Maybe the environment is to blame.

What if invisible chemicals in the environment from things like detergents, pesticides and fertilizers are getting into our food, then our bloodstreams and misdirecting our fat cells? What if these chemicals are mimicking estrogen in our bodies, making girls hit puberty earlier and putting them at risk for cancer?

Biro, director of adolescent medicine at Cincinnati Children’s, and his team of researchers are searching for those answers. They are studying endocrine-disrupting chemicals in the environment that influence the way hormones are made or where they act.

A special group of these chemicals, known as obesogens, may influence fat cell production and function.

The structure of endocrine-disrupting chemicals often closely resembles estrogen, Biro says. Researchers are trying to figure out whether those chemicals can take over in the body and if these obesogens can reprogram the way our fat cells work.

Biro and his colleagues are studying growth in girls and zeroing in on early hormonal changes to pinpoint the impact on the timing of puberty and, potentially, a girl’s risk of developing cancer  later in life.

“Puberty serves as a window of susceptibility,” Biro says. “Those things that impact the timing of pubertal maturation might also impact that window of susceptibility.”

Triggering trouble

Most people have never heard of “obesogens,” but the American Medical Association, the National Institutes of Health, the Environmental Protection Agency and the White House Task Force on Childhood Obesity are all putting money into finding out more about them. Men’s Health magazine editor Stephen Perrine’s book, “The New American Diet,” explains how obesogens mess with our metabolism. Even Oprah-famed Dr. Oz did a show on “Obesogens: The Chemicals You’re Eating That Make You Fat.”

Pediatric researchers at Cincinnati Children’s have good reason to explore this idea. They want to know whether chemicals in everything from plastic food packaging to processed foods can program the timing of puberty, as well as the way girls gain weight, and set them up for more health problems.

Animal studies suggest exposure to endocrine disruptors can disrupt an animal’s hormonal system and sexual development, Biro says. Researchers want to know how that translates in children. Do these chemicals confuse our hormones and hijack the regulatory system to trigger weight gain? Do they affect the timing of puberty? Do they put girls more at risk for cancer?

“There are probably about a dozen cancers associated with obesity — higher risks of endometrial cancer, higher risk of breast cancer in the post-menopausal period, higher risk of colon cancer, higher risk of a specific type of esophageal cancer,” Biro says.

“Just colon and breast cancer are two of the three top cancer killers and have a clear association with obesity,” he says. “So how are these changes associated with each other? Are some of these changes being elicited by exposure to environmental chemicals? Are some of these chemicals hitting the fat cell and hitting the products of the fat cell? We are working to understand that better.”

A new look at puberty

Biro may be best known for his research published last year in the journal Pediatrics about more and more girls hitting puberty as young as age 7.

He said then that while it is too early to pinpoint any one cause, the rise in the rate of childhood obesity is a factor, and researchers have noted that heavier girls are more likely to start puberty earlier.

He also pointed to another possible culprit: hormone-disrupting chemicals. That is where his research is expanding. He hopes the work results in more definitive information about the relationship between body mass index, chemical exposures and timing of puberty.

Biro is the primary investigator of the Cincinnati site for the Breast Cancer and Environmental Research Program, a study that involves participants at Cincinnati Children’s, Kaiser Permanente in San Francisco and Mount Sinai School of Medicine in New York. Researchers are following 1,239 girls who were recruited when they were 6 to 7 years old to figure out what effect chemicals have on their hormones as they mature. The $4.6-million NIH study here will continue for five more years, following the girls throughout the time when most of them will experience menarche, their first menstrual period.

“We are trying to follow up on some of the epidemiologic links with breast cancer,” Biro says. “This is not a study of breast cancer, but looking at those changes that can be associated with breast cancer, in the way that earlier age of first menstrual period is associated with an increased risk of breast cancer.”

He is taking a closer look at how the timing of puberty might change a girl’s risk of breast cancer.

Traditionally, puberty in girls has been defined as the onset of breast development. But Biro says that is actually a relatively late phenomenon in puberty. His research indicates that sex hormones increase before breast development begins. His team is working on a mathematical model to determine whether reaching adult height is a better marker for the timing of puberty. They also are studying how a girl’s first menstrual period and breast development figure in and relate to her risk of breast cancer.
“Things that cause changes in the timing may also cause changes in one’s risk,” Biro says. “Not just because of the change in the timing, but it’s impacting some of the same biochemical processes that could impact other adult morbidity and mortality.”

Biro and his colleagues gather data on girls in the study during yearly exams. They record each girl’s height, weight, hip and waist circumference and skin folds, do bone density and body fat screenings and examine blood and urine samples for chemical exposures. Researchers also look at insulin and glucose levels, do lipid profiles and look at hormones that are related to metabolic control. They want to know when a girl reaches her peak height, how her fat is distributed around her abdomen and how resistant her body is to insulin.

“The other factor is that some of these environmental exposures that lead to earlier puberty could also be impacting the breast at that time,” Biro says. “When you have these very metabolically active cells undergo division and transformation, they’re more susceptible to environmental exposures.”

Is greener living the answer?

The theory behind much of Biro’s research is that when puberty arrives earlier, the window of exposure to obesogens opens wider and increases a girl’s risk of getting breast cancer later in life.

The implications of these risks of chemical exposure make him an advocate for young girls — and their families — to live more healthfully.

He recommends buying organic for fruits and vegetables most likely to be hit by pesticide use (see breakout box for details) and looking for safer alternatives to avoid potentially harmful chemicals.

Biro himself avoids microwaving food in plastic containers. He grows many of his own vegetables and buys as much as he can from local farmers.

“Our genes have hardly changed at all in 25,000 years,” he says, “yet the environment is completely different from what it was even 50 years ago.”

“I’m just going to suggest to people that they try to live a little bit greener,” he says. “Mother Earth would be happy with that but I think that the human body would probably respect it as well.”

We still need to understand more about chemical exposures and possible links to diseases, Biro says. Learning more about puberty will help researchers at Cincinnati Children’s advance what we know about adult diseases as well, he says.

“Ultimately, what we’re trying to do is understand some of the pre- and peri-pubertal processes and how they impact adult morbidities so that we can all live healthier,” he says. “Some of the data that we’re pulling together right now is going to change the way we think about puberty in girls.”