by DINA FINE MARON
ILLUSTRATION/Melody Newcomb
Increases in obesity appear to be the major culprit, but family stress and exposure to chemicals may also play a role
For the past two decades scientists have been trying to unravel a mystery in young girls. Breast development, typical of 11-year-olds a generation ago, is now occurring in more seven-year-olds and, rarely, even in three-year-olds. That precocious development, scientists fear, may increase their risk for cancer or other illnesses later in life. Time has not resolved the puzzle. Nor is there any indication that this trend is slowing. More and more families are finding themselves in the strange position of juggling stuffed animals and puberty talks with their first and second graders.
Obesity appears to be the major factor sending girls into these unchartered waters. The rate of obesity has more than doubled in children over the past 30 years. And whereas only 7 percent of children aged six to 11 were obese in 1980, nearly 18 percent were obese in 2012. The latest studies, however, suggest that weight gain does not explain everything. Family stress and chemical exposures in the environment may also play a role, but the data do not yet paint a very clear picture of their contribution. As for boys, the data are murkier, but one 2012 study did suggest that they, too, may be starting puberty earlier than before—perhaps by as much as six months to two years.
Clinicians say that slightly early development of breasts is likely not physically harmful and so does not require medical or pharmaceutical therapy for most girls. (Among the few exceptions are pituitary disorders.) The psychological effects, though, are another matter that warrants more attention from schools and parents; early puberty seems to augment the risk of depression and to promote substance abuse and early initiation of sexual intercourse.
Obesity’s role
Precocious development was first thrust into the spotlight in 1997, when a landmark U.S. study declared that at least 5 percent of white and 15 percent of black girls had started to develop breasts by age seven—much earlier than expected. “That finding evoked a lot of passion,” says Paul B. Kaplowitz, a pediatric endocrinologist at Children’s National Health System in Washington, D.C. Moreover, the 1997 work found that the trend toward early development was not happening only in outliers. Puberty was happening earlier in most girls and again differed by race: instead of age 11, the typical age of breast development by the early 1990s was 8.87 years in African-Americans and 9.96 in white girls, researchers found. Other studies soon reached similar conclusions in Europe as well as the U.S. According to the most recent U.S. data (from 2013), 23 percent of black girls, 15 percent of Hispanic girls and 10 percent of white girls have started to develop breasts by the age of seven. Those findings suggest the proportion of girls with significantly earlier breast development may still be ticking upward.
Scientific American for more