(WOMENSENEWS)--Emily de Reyna started early.
Developing breast buds at age 4, body odor at 5 and pubic hair at 6, she hurtled toward puberty so quickly that when she was just 6 and a half years old, her parents followed an endocrinologist's advice and started giving her Lupron, a drug that curbs estrogen and other hormones that stimulate menstruation.
Now 9, Emily is tall for her age but has yet to get her period.
"To me, starting to menstruate in early elementary school seemed unfathomable," says Emily's mother, Denise de Reyna, who lives in New York's Long Island suburbs.
Given the fact that Emily has always been chubby, her precocious development may not be so unusual. She stands 4 feet 10 inches and weighs 105 pounds, technically overweight, as are a growing number of other U.S. girls who are entering puberty early.
This month, a study in the journal Pediatrics showed that being overweight spurs early breast growth in girls.
Another March study, in the Journal of Adolescent Health, found the average age of first menstruation, or menarche, declined from 13.3 years in girls born before 1920 to 12.4 years in those born during the early 1980s.
Researchers say girls' widening girths are likely responsible for both trends. According to the Atlanta-based Centers for Disease Control and Prevention, 16 percent of girls ages 6 to 11 are overweight, a fourfold increase since 1971.
Age of Puberty Declining
Though research linking weight to puberty dates back for centuries, the recent Pediatrics paper was the first to peg which comes first. It indicated weight gain triggers early puberty, instead of early puberty triggering weight gain.
In the United States in the early 1800s, breast buds and menarche arrived around ages 13 and 16 respectively. Those changes now come around ages 9 and a half and 12 and a half.
Scientists say girls are eating more food and putting on pounds, which is causing their bodies to boost production of the hormone leptin.
"Leptin is made in fat cells and is necessary for normal reproductive function," says Paul Kaplowitz, chief of endocrinology at the Children's National Medical Center in Washington and author of "Early Puberty in Girls," published in 2004 by Random House. "There's an evolutionary benefit to this. You don't want to get pregnant if there isn't enough food for you to carry a pregnancy successfully. You would risk the baby's life and your own."
According to the recent Pediatrics study, obese girls are twice as likely as normal-weight girls to sprout breasts early. Overweight girls are 50 percent more likely to do so. Being overweight as early as age 3 was found to be a marker for premature breast development.
While the age of breast growth seems to be declining, the age of menarche seems to be leveling off.
"In the past, girls could have breast buds at 9 and their periods three years later, at 12," says Kaplowitz. "Now, they might have breast buds at 7 and their periods five years later, still around age 12."
Signals of Later Problems
The bad news is that early development of any sort--from pubic hair to body odor to the "pubertal growth spurt" that doubles girls' rate of height gain--may cause problems.
"Girls with earlier onset of puberty have a higher risk of behavioral problems, earlier initiation of alcohol use and earlier sexual intercourse," says Joyce Lee, an endocrinologist at the University of Michigan in Ann Arbor and author of the Pediatrics paper. "They also have higher rates of anxiety, depression, adult obesity and breast cancer."
In addition to weight gain, a number of factors can accelerate female puberty.
Girls whose mothers developed young are likely to do the same. And girls in different racial groups mature at different rates. In 1997, a Pediatrics study found the average African American girl starts developing breasts at 8.8 years, while the average white girl does so at 9.9 years. This month's Journal of Adolescent Health study found non-Hispanic blacks menstruate earliest (at 12.06 years), followed by Mexican Americans (at 12.09 years) and non-Hispanic whites (at 12.52 years).
Like genetics, home environment can also play a role. Research shows that girls raised in households without their father present are likely to hit puberty young and that having an unrelated male such as a stepfather present speeds the process even more.
Pollutants can also hasten maturity. In separate studies, Michigan girls accidentally exposed to polybrominated biphenals (chemicals used in flame retardants) started their periods a year younger than average; Puerto Rican girls exposed to phthalates (chemicals that soften plastic) had breast buds as early as age 2; and African American girls who used hair products containing human placenta also developed breasts at age 2.
"Exposure to DDT (dichloro-diphenyl-trichloroethane, a pesticide) and PCBs (polychlorinated biphenyls, chemicals used in manufacturing) may lead to early puberty," says Walter Rogan, an epidemiologist at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C. "But research on environmental factors has so far been inconsistent."
Other factors that may be linked to early puberty include low birth weight (under 5.5 pounds); eating dairy and meat products treated with hormones; and eating soy and other foods with high levels of "phytoestrogens," plant substances that mimic human estrogen.
Sociologists also point to the "hypersexualization" of U.S. culture, where mainstream magazines flaunt near-nudity, where girls' dolls are voluptuous and where girls' bodies may in response be preparing for sexual intercourse earlier than ever before.
To better track the physical causes of puberty, the Bethesda, Md.-based National Institutes of Health has launched a study of 14,000 children born in 2001 that is "longitudinal" and will follow its subjects over time. The results of this research will not be available for 10 years or more.
Just as early development's mechanisms require more study, so too do its psychological effects.
Emily de Reyna, for her part, seems to be adjusting well. Her mother says that when a boy recently teased Emily about her "boobs," she replied, "They're called breasts, and I have them because that's what girls have."
Kaplowitz says, "If girls with early puberty are in supportive home environments like Emily's, most of them will do fine. Parents can talk to them and give them special books to read. Kids will likely handle it better if they are prepared and if these changes don't come as a surprise."
Marcia Herman-Giddens, an adjunct professor of public health at the University of North Carolina at Chapel Hill, takes a more cautious approach. "Girls' bodies may be developing young, but that doesn't mean their brains and judgment are developing, too," she says. "Seven and 8-year-olds don't need to be dealing with sexual changes. Instead, they just need to be kids. If we gave them enough exercise and stopped giving them junk food--and if we cleaned up the environment--the age of puberty might go up again."
Molly M. Ginty is a freelance writer based in New York City.
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