Signs of Puberty Seen Earlier in White Girls

(MedPage Today) -- The number of white girls developing signs of puberty at a younger age has almost doubled since the late 1990s, researchers found.

A longitudinal study of more than 1,200 girls examined between 2004 and 2006 found that 10.4% of the white 7-year-old girls had begun to mature -- as determined by the presence of palpable breast buds -- according to Frank Biro, MD, of Cincinnati Children's Hospital Medical Center, and colleagues.

That's twice the percentage of girls with early maturation (5%) seen in a 1997 study (P<0.001), Biro and co-authors reported in the September issue of Pediatrics.

A similar difference was seen among 8-year-old white girls (18.3% versus 10.5%, P<0.002), they added.

The percentage of black girls who had begun to mature at ages 7 and 8, however, was not significantly different between the two studies -- suggesting that white girls were continuing to develop at younger ages, whereas timing of puberty had stabilized among black girls.

Increases in body mass index may be to blame for earlier maturation, Biro told MedPage Today.

"Our study comes on the other side of the obesity epidemic that's occurred not only in this country but other countries around the world," he said, "and we think that one of the more important contributing factors is the higher body mass index in the girls in the 21st century."

Another possibility is exposure to endocrine disruptors from household and personal care products, Biro said, although future studies will try to definitively identify reasons for a declining age at the initiation of puberty.

Biro and his colleagues collected information on 1,239 girls from three centers taking part in the Breast Cancer and the Environment Research Centers consortium, set up to explore potential environmental influences on breast cancer.

Early puberty (specifically early age at menarche) is considered a risk factor for breast cancer. This is thought to be partly due to greater lifelong exposure to female hormones (estrogen and progesterone) and to susceptibility of rapidly developing breast tissue to environmental exposures

Participating centers were the Mount Sinai School of Medicine in New York City (in East Harlem), the Cincinnati Children's Hospital and the University of Cincinnati (the Cincinnati metropolitan area), and the Kaiser Permanente Northern California and the University of California San Francisco (in the San Francisco Bay area).

The group of girls studied was multiethnic -- 33.7% non-Hispanic white, 31.6% non-Hispanic black, 29.9% Hispanic, and 4.6% Asian.

Physicians, nurse practitioners, or research staff at each center assessed each girl for the presence of maturation, defined according to the Tanner criteria for breast maturation. Girls with at least breast stage 2 -- defined as a palpable breast bud with enlargement of the areola -- were considered to have begun puberty.

At age 7, 10.4% of white, 23.4% of non-Hispanic black, and 14.9% of Hispanic girls had attained breast stage 2 or higher.

At age 8, the percentages were 18.3%, 42.9%, and 30.9%, respectively.

Biro said it was unclear why the onset of puberty appeared to be falling in white girls but not in black girls, but speculated that it may be that black girls -- who mature at younger ages, have already reached a minimum biological age for maturation.

Earlier maturation for all girls could have a number of adverse consequences, including lower self-esteem, less favorable body image, and greater rates of eating problems, depression, and suicide attempts, according earlier studies cited by Biro and his colleagues.

Biro noted also that girls who mature earlier may be expected to act in a more mature manner, and may be pushed into behaviors they are not ready to engage in. Indeed, previous studies have found that girls who entered puberty earlier started having sex at a younger age.

Entering puberty at a younger age is not only a risk factor for breast cancer, but also for endometrial cancer, hyperinsulinemia, and elevated blood pressure.

The authors acknowledged some limitations of the study, including the fact that the sample was not nationally representative, low recruitment levels, and baseline differences in maturation by site, which suggests different dietary patterns, chemical exposures, racial and ethnic differences, or interactions between these areas.

The study was supported by grants from the National Institute of Environmental Health Sciences and the National Cancer Institute. Mount Sinai School of Medicine, one of the centers participating in the study, acknowledged support from the NIEHS, Environmental Protection Agency, Agency for Toxic Substances and Disease Registry, and National Center for Research Resources. The Cincinnati site acknowledged receiving grant support.

The authors reported that they had no conflicts of interest.

This article was developed in collaboration with ABC News.