Vol. 06 Issue 1, Winter 2001
Diana Zuckerman, Ph.D PhD
Executive Director, National Center for Policy Research for Women & Families Washington, DC Cornell University Pesticide Management Education Program (PMEP)
There are new guidelines for pediatricians that are guaranteed to shock: girls who start to develop breasts and pubic hair at age six or seven are not necessarily "abnormal" (Kaplowitz, et al., 1999). In fact, by their ninth birthday, 48% of African American girls and 15% of white girls are showing clear signs of puberty.
The new guidelines, developed by the Lawson Wilkins Pediatric Endocrine Society and published in the journal of the American Academy of Pediatrics, Pediatrics, are based primarily on a study of more than 17,000 girls between the ages of three and 12 who were patients in more than 200 pediatricians' offices across the country (Herman-Giddens, et al., 1997). The study, by Marcia Herman-Giddens, DrPH, and her colleagues at University of North Carolina School of Public Health, is unique, making it difficult to know exactly how the age of breast and pubic hair development has changed over time. Previous standards of "normal puberty" were set more than 30 years ago, based on a study of less than 200 girls in a British orphanage in the 1960s (Marshall and Tanner 1969).
Based on the new pediatric guidelines, pediatricians are less likely to prescribe monthly hormone shots to slow down puberty for these young girls. Although evaluation and treatment remains important for very young girls showing signs of puberty, the new criteria have redefined what is considered normal and abnormal. The pediatricians decided that these hormone shots are usually not necessary, since girls who start puberty early will develop normally - that is to say, they will grow to their full height. But the implications for parents, teachers, and others who work with children are equally important: many young girls in early elementary school are developing breasts and pubic hair at a time when they are still playing with dolls and Junior Monopoly, and are too young to understand the emotional mood swings and other symptoms of adolescence. In addition, the long-term health implications for cancer and other diseases are unknown, but there is reason to be concerned.
Before we can examine the likely psychological impact or long-term health implications, we need to understand the data. They were gathered from a cross-sectional study conducted in pediatric practices that participate in the American Academy of Pediatrics' Practice-Based Research Network. Practices were recruited from the network which had 632 self-selected clinicians in 155 practices located in 34 states and Puerto Rico. Sixty-five practices participated in the study. Ninety percent of the girls studied were white, and most of the others were African American.
Pediatricians, nurse practitioners, and physician assistants examined three- to 12-year-old girls between July 1992 and September 1993. Girls were recruited who came for a well-child visit, or for a problem that would routinely require a complete physical.
Results found that in their seventh year, 27% of African-American girls and 7% of white girls had begun breast development and/or had pubic hair. Between ages eight and nine, those numbers had increased to 48% of African-American girls and 15% of white girls. Also at age eight, 17% of African-American girls and 2% of white girls had axillary hair.
Menarche occurred in the girls' eleventh year for 28% of African-American girls and 13% of white girls. At age 12, 62% of African-American girls and 35% of white girls had begun menstruating. For white girls in the US, the age of first menstruation has remained stable over the past 45 years. In African-American girls, age at menarche has declined by about six months in the past 20 to 30 years. The authors felt that the change in age at menarche in African-American girls may be due to their coming closer to achieving optimal nutritional and health status.
Girls in this study were taller and heavier than in the first and second National Health and Nutrition Examination Surveys (NHANES, which occurred more than 20 years ago), especially the older girls. Girls in the study who had one or more secondary sexual characteristic were larger and heavier than girls who had not begun puberty. A 1994 report on the National Growth and Health Study found a similar increase in the height and weight of nine and 10-year-old African-American and white girls compared to results from previous NHANES studies. The mean onset age for breast development was 8.9 years for African-American girls and 10.0 for white girls. Pubic hair onset began at age 8.8 for African-American girls and 10.5 for white girls. Axillary hair appeared at the average age of 10.1 in African-American girls and 11.8 in white girls. All of the characteristics emerged significantly earlier in African-American girls both with and without controlling for height and weight.
Although there are few other sources of data to compare these new findings to, the authors state that white girls in their study appear to be developing six months to one year earlier than girls in earlier studies. There are no data available to determine whether African-American girls are developing breast and pubic hair earlier than in past years, although the data indicating earlier menarche suggest that this is likely.
We don't know what causes the disparity between white and African-American girls. A number of previous studies in the US have noticed earlier development and larger pre-pubertal size of African-American girls compared to white girls. Several studies in the 1970s and 80s found African-American girls to be taller, heavier, and maturing earlier than white girls their age.
In addition to their differing size, another hypothesis about the racial discrepancy is that hair products used by African-Americans that contain estrogen or placenta may be increasing the prevalence of early puberty.
The Herman-Giddens study has received a great deal of attention, and some have questioned whether it represents all girls in the US. The pediatric practices and the girls selected were not a random sample, and it is possible that girls with evidence of early pubertal development were more likely to be brought in for a doctor's visit because their parents were concerned. Of course, parents might also be likely to bring in older girls who had not yet shown pubertal development, and that would have balanced that selection bias. There is no evidence that these kinds of selection biases occurred. On the contrary, in my experience, many physicians and many mothers have commented on their observation that girls seem to be maturing much earlier than they did 30 to 40 years ago. And, the pediatric endocrinologists changed their guidelines because they believe the findings from the Herman-Giddens study.
If girls are starting puberty earlier, it is important to determine the potential causes and consequences. Many scientists believe that earlier puberty is caused, in part, by the widespread exposure to pesticides and other chemicals that have qualities like estrogen. There are a number of studies showing that chemicals that disrupt the endocrine system can affect pubertal development or sexual behavior in animals (Guillette, et al., 1994; Howdeshell, et al., 1999; Yamomoto et al., 1996). Those studies, and many others implicating the effects of endocrine-disrupting chemicals on reproductive function, were described in the seminal work, Our Stolen Future by Coburn, Dumanoski, and Myers (Coburn, et al., 1996). In addition, there are studies in people that show a correlation between exposure to endocrine-disrupting chemicals and changes in pubertal development. One of the most provocative studies shows that Puerto Rican girls who have premature breast development have higher blood levels of a particular type of chemical called phthalates, used in many cosmetics, toys, and plastic food containers (Colon, et al., 2000). A recent study by the Centers for Disease Control and Prevention showed that women of childbearing age have the highest levels of phthalates in their blood, perhaps putting their future children at risk of early puberty or other reproductive problems (Blount, et al., 2000).
Dr. Paul Kaplowitz from the Medical College of Virginia, co-chair of the panel that wrote the new pediatric guidelines, believes that "at least part of the explanation is overweight" since a certain amount of body fat is required for normal reproductive function. Fat cells manufacture leptin, a hormone that might be involved in triggering puberty. If girls get to a higher level of body fat and secrete enough leptin a few years earlier than they did in the past, it is possible that the first signs of puberty could emerge earlier. However, since puberty often causes weight gain, it is difficult to determine whether obesity causes early puberty or vice versa.
The long-term health risks of early puberty also deserve attention. It has already been demonstrated that girls who begin menstruating at a very young age have an increased risk of developing breast cancer as adults, so it is certainly possible that earlier onset of puberty may also put girls at greater risk of breast cancer. Since most girls who experience early signs of puberty do not necessarily have earlier menarche, further study is needed to determine whether they will have an increased breast cancer risk.
There is research evidence that early puberty may put young girls at risk for emotional and social problems that could be devastating. Maturing young girls will have to cope with their own confusing sexual feelings as well as the impact that their maturing appearance has on boys and men. Research indicates that girls with early menarche face consequences as young girls and as teenagers. Studies of young girls indicate that those who develop early are more likely to be depressed, aggressive, socially withdrawn, and moody (Sonis, et al., 1985). Studies of teens indicate that girls who developed early are more likely to be sexually active, have more problems in school, and are more likely to smoke and use alcohol and drugs (Phinney, et al., 1990; Ge, et al., 1996; Graber, et al., 1997).
As a think tank concerned about the health and well-being of women and families, the National Center for Policy Research for Women & Families is examining the causes and consequences of early puberty, and identifying policies that can help to reverse the trend. CPR is also partnering with other experts and organizations to help girls and their families who already must cope with this problem. Additional information is available on CPR's website at http://www.center4policy.org
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