Are children today really going through puberty earlier?
As a result, most studies of early puberty focus on girls—but those assessments aren't much better. Herman-Giddens' 1997 study relied only on visual inspection by hundreds of different pediatricians trained in different programs, and not on actually feeling systematically for the small, firm masses that typify breast buds. That might lead obese kids to be prematurely termed pubertal.
There is a much clearer and defined marker of puberty: the age of a girl's first period, or menarche. If puberty is occurring earlier, one would think menarche should also, since the process responds to the same cascade of hormones. But in the past 40 years, there hasn't been any real change in age of menarche, which remains at just over 12 years. Additionally, no researcher has shown any objective change in the timing of adolescent growth spurts. In 2008, an international group of endocrinologists and other experts led by the U.S. Environmental Protection Agency found little agreement that puberty was happening much earlier.
Perhaps researchers seeing widespread precocious puberty are just noticing breast development earlier—looking harder at normal bodies. It would follow that today's puberty would seem to take longer than in previous decades. That's precisely the case. (Epidemiologists call this "lead-time bias.")
It's possible that obesity might correlate with earlier puberty in some girls (oddly, fat boys appear to have later puberty than other boys), though the population-wide effect is still imperceptible by objective measures. And there are plenty of other reasons to worry about toxins like BPA or phthalates.
But in the end, the epidemic of earlier and earlier puberty is a myth that the media love and certain researchers continue to propagate. The tale's promotion doesn't always depend on data. Instead, worries about earlier physical maturation in girls sublimate and propel concerns about society's sexualization of young girls, whether by provocative dance routines or revealing clothing. Those topics certainly get people talking. Unfortunately, any solutions are unlikely to come from the labs of our nation's endocrinologists.
Darshak Sanghavi is Slate's health care columnist. He is chief of pediatric cardiology and associate professor of pediatrics at the University of Massachusetts Medical School as well as the author of A Map of the Child: A Pediatrician's Tour of the Body. Follow him on Twitter.
Illustration by Robert Neubecker.