| Main Feature Story - Friday, February 16, 2007
Feature: Girl, You'll Be a Woman Soon
Environmental factors are herding girls into womanhood sooner than ever
By Ronnie Cohen
When biologist and author Sandra Steingraber began researching early puberty in girls, she used a medical Internet search engine and inadvertently came across veterinary studies of puberty in cattle.
"If you're a dairy farmer," Steingraber said she learned, "you want to get your cows to early puberty. Wean early, confine them and put them on a high-calorie diet. That is exactly what we're doing with our kids."
The San Francisco-based Breast Cancer Fund recently hired Steingraber to write a paper, scheduled for publication in July, on the causes and consequences of early puberty. Steingraber said she hopes her work will raise questions for scientists conducting puberty studies—including a long-term examination of Marin County girls—and will influence policymakers to promote breast-feeding, healthy diets, physical education programs and environmental protection.
Unlike in cows, research shows nothing good can come from early puberty in girls, Steingraber told about 100 people attending a talk she gave in San Francisco last month. A cancer survivor and expert on environmental links to cancer, Steingraber has been called the Rachel Carson of our time and the poet laureate of the environmental-health movement.
"Early puberty is really bad for girls," Steingraber said. "It raises the risk for drug abuse, alcohol abuse, depression, violent victimization for a long time to come. Girls who enter puberty early are disproportionately represented in the criminal record, found to earn less money."
When a girl goes through puberty, her brain is remodeled to allow abstract thinking, Steingraber said. But the development of higher-order thought comes at a price. Once a girl passes puberty, her brain loses its childhood plasticity, and she has a harder time learning to speak a foreign language with an accent or to play a sport or a musical instrument.
"Early puberty is a risk factor for breast cancer," she said. "But it's not considered a modifiable risk factor. But perhaps age at puberty is modifiable on a societal level or an environmental level."
During a question-and-answer period, a couple of mothers asked Steingraber, herself a mother of two young children, what they could do to protect their daughters from entering puberty early. In response, Steingraber underlined her commitment to working toward political change in an effort to protect all children.
"I'm really interested in public health," she said. "I'm really not interested in putting my children in a bubble of safety and guiding them through a toxic world. I do buy all organic food for my family. I do that as a political act to direct my money to organic agriculture and hopefully protecting my kids at the same time."
Steingraber said her reading of the literature on early puberty reinforced her decision to feed her children only organic food and to keep television out of her home.
But, she said, "As a mother and a full-time biologist, I have limited time and would rather direct my efforts at a political-social level."
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IN 1997, STEINGRABER wrote Living Downstream: A Scientist's Personal Investigation of Cancer and the Environment. In a telephone interview from her home in Ithaca, New York, Steingraber, who had battled bladder cancer in her 20s, said that after examining all the studies on puberty she could find, "What I finally came away with is realizing that sexual maturation is not governed by a biological clock. It's really not an adequate metaphor for our reproductive lives. We have kind of hijacked that system and bombarded it with signals that speed the whole process up."
Steingraber said she was surprised to learn that, despite the perception of a steep drop in the age at which girls begin menstruating, the age has remained relatively stable since around 1970.
"There's a lot of folk biology out there that the average age of puberty is falling," Steingraber said. From what she gathered from the only available data (which she called "sloppy"), Steingraber figures the average age of menarche, or the beginning of menstruation, for American girls has dropped from 12.8 years old to 12.6 years old in the past 35 years.
"The real story is thelarche—the development of the breasts," she said. By 8 years old, she said, 14 percent of American girls have breasts. "Now, when you walk into a schoolhouse, you see fifth-graders who look a lot different than we used to look," the 47-year-old biologist said.
She believes puberty is unfolding more slowly than it once did, taking about four-and-a-half years from the time girls first start developing breasts until they are fully developed. And, for reasons scientists do not yet fully understand, African-American girls are developing on average a year earlier than other girls.
One hypothesis for the difference in race may shed light on the reason for the lowered pubertal age in general. Researchers believe African-American girls may use more personal-care products that contain chemicals that mimic the female hormone estrogen than their white counterparts.
Infant girls actually are born in puberty (which explains why newborns get acne) with their ovaries producing estrogen, Steingraber said. After three months or so, for an as-yet unexplained reason, puberty turns off for about 10 years.
Steingraber offered a range of hypotheses about factors influencing the age of puberty. Low birthweight and preterm babies tend to enter precocious, or especially early, puberty more often. Precocious puberty starts at age 7 for white girls and age 6 for African-American girls.
Obesity and increased body size, calorie-dense diets and sedentary lifestyles increase risk for early puberty. Breast-fed babies tend to go through puberty later. Exercise also delays puberty, said Steingraber, who runs every day.
A stressful home environment tends to speed puberty's onset, as does watching television and living without a father, though in parts of Africa where fathers are regularly absent, living without a father does not have the same effect, Steingraber said. Girls who live in homes with unrelated males may start puberty earlier.
• • • •
RESEARCHERS HAVE STUDIED hormones that appear to trigger puberty, but they do not yet know how the process works.
In Michigan, girls entered puberty early as a result of their pregnant mothers eating dairy and meat contaminated with a fire retardant containing the chemical polybrominated biphenyl. The fire retardant was inadvertently mixed with cattle feed in place of a feed additive in 1973. Scientists linked precocious puberty in young girls in Puerto Rico with plasticizer chemicals called phthalates. Used to make vinyl plastic flexible, phthalates are ubiquitous in our environment—in children's toys, nail polish, perfumes, shower curtains, water and baby bottles and flooring.
Another culprit linked to precocious puberty has been skin creams men use to enhance sexual performance. Premature puberty develops in girls when couples using these creams also allow their infant or toddler to sleep in the parents' bed.
In Marin County, where breast cancer rates have been disproportionately high, epidemiologists are studying 102 6- to 8-year-old girls to see how prepubertal exposures influence the onset of puberty. The five-year study is part of the federally funded Breast Cancer and the Environment Research Centers, a consortium of four centers. The other centers are in New York and Cincinnati.
While one arm of the study examines girls going through puberty, another arm is investigating breast development in animals. Altogether, the centers are examining 1,200 girls, 444 in the Bay Area. The Bay Area study began a year-and-a-half ago and will continue through 2010, or longer, if researchers can secure additional funding, said Larry Kushi, associate director of epidemiology for Kaiser Northern California.
Researchers are investigating weight, diet, physical activity levels, stress, household structure, time spent watching television, use of personal-care products and medical exposures, among other things. They also will look at how often the girls' homes are fumigated, whether they drink water from plastic bottles and if their showers have vinyl curtains.
Investigators are examining the girls once a year and collecting blood and urine samples, which they will analyze for additional clues about influences on puberty and disease.
Already, Kushi said, "We see fairly striking racial or ethnic differences." African-American girls show signs of earlier pubertal onset, he said. He added that 30 percent—or twice the percentage he expected—of the Kaiser girls in the study are at risk for becoming overweight or obese.
Kushi, whose father, Michio Kushi, introduced modern macrobiotics to the United States in the 1950s, finds the possible connection between early puberty and red meat intriguing. Cattle ranchers insert female hormones into the ears of some 90 percent of the livestock in the U.S., Kushi said. Kaiser is asking girls in the study about their meat consumption but, Kushi said, "I don't know if we'll be able to disentangle this."
Researchers expect the Kaiser study group to be particularly useful in understanding the influences on puberty. Because the Kaiser girls have been members of the health-maintenance organization since birth, researchers have access to their lifelong medical charts.
The Bay Area Breast Cancer and Environment Research Center will hold its second annual town hall meeting to discuss "Environmental Influences on Girls' Development During Puberty" Saturday, March 10 from 9:30am-2pm in the new San Francisco State University downtown campus. For more information or to register, contact Jo Ann Johnson at 415/507-1949 ext. 103 or joannj@zerobreastcancer.org.
E-mail Ronnie Cohen at ronniecohen@comcast.net.
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