puberty occurring earlier in American girls, and if so, why?
Marcia Herman-Giddens and colleagues published their
landmark study in 1997 about a reduction in the age of puberty
among American girls, alarm bells went off in the public and in
the media. Based on thousands of girls around the country, the
study suggested that black and white American girls were reaching
puberty on average as much as a year earlier than expected based
on historical data. The study reinforced anectodal reports and
public impressions that girls were maturing earlier, sometimes
much earlier, than usual. Parents and the press raised questions
about why it was happening and what might be the consequences.
Time Magazine, for example, ran a cover story, "Teens
before their time."
only did the average age of puberty appear to be decreasing, but
significant numbers of girls were maturing sexually long before
the average. For example, Herman-Giddings' work revealed that
by age 8, 48%
of black girls and almost 15% of white girls were showing signs
of sexual development.
work stimulated great public interest. It has met with several
people have challenged the basic finding. The principal criticisms
of Herman-Giddens et al. are (1) that historical data
are insufficient to allow a comparison; and (2) that the sample
used in the study is not a random sample of the population.
Instead it is composed disproportionately of children brought
to see a pediatrician.
pediatricians have recommended
that medical standards be revised so that girls developing at
the average rate described by Herman-Giddens et al. be
considered normal. This recommendation has been challenged by
others, who argue (1) that there is insufficient proof of a
change in rate of sexual development, (2) that changing the
standards would make it less likely that girls needing medical
intervention because of physiological problems would receive
appropriate medical care; or (3) that changing the standards
then undermines efforts to identify the causes of changes, if
they are occurring.
attention has focused on what factors might be causing the changes,
if they are real. The three leading hypotheses are (1) increases
in the prevalence of obesity; (2) changes in social factors,
particularly the absence of the biological father in the home
and the presence of a male other than the biological father;
and (3) contamination effects, particularly in the womb.
are no certain answers on any of these issues.
causation: data support each of the leading
hypotheses. It may be that all are involved, or it may be that
some cases (for example the case of
premature thelarche in Puerto Rican girls) have one cause, others
another (e.g., PBBs causing early
menarche in Michigan).
case for contamination affecting
sexual development in animals is very strong, as is documentation
of human exposure to those very contaminants. An additional complication
is that, at least in laboratory animals, there is evidence that
contamination can contribute to obesity.
methodological criticisms: While Herman-Giddens et al.'s
methodology can be criticized, their study cannot be dismissed out
of hand. In response to criticisms
about potential bias in the sample, Herman-Giddens
replies that "although the subjects were not randomly selected
and, therefore, might not be representative of the population at
large...the large number of girls studied would make it unlikely
they were different from the population as a whole." And while
Herman-Giddens et al. do not address this in their response
to criticisms, even if the average age of pubertal development has
not changed, it is important to understand why such a notable
percentage of very young girls are showing signs of sexual development.
changing medical standards: Some of the criticisms suggested
that Herman-Giddens et al. were arguing that the change meant
that younger age of puberty should then be regarded as normal, and
as not meriting medical intervention. This was one of the complaints
conveyed by a confused
pair of articles written by Gina Kolata in the New York Times
in late February, early March 2001. To the contrary, Herman-Giddens
et al. were not recommending a change in medical standards.
They are concerned that young women developing early not be subjected
inappropriately to unnecessary medical intervention, but that both
the causes of the trend they discovered be identified and individual
cases be addressed appropriately by medical professionals.
example, in the March 2001 issue of Pediatrics, Herman-Giddens
et al. review a case history in which a group of pediatricians
report that a young woman showing early development did not receive
an evaluation because her development fell within the pattern of
the 1997 Herman-Giddens study. Herman-Giddens et al. respond
by stating first that by their criteria, in fact the girl in question
should have been evaluated. They then observe that "we are
concerned that our study may be used inappropriately to deter clinicians
from referring girls with very early puberty if the findings of
our study are not carefully reviewed."
RL et al. 2000. Current
age of onset of puberty. Letter to the Editor. Pediatrics.
ME et al. 2000. In
ME et al. 2001. Early
puberty: a cautionary tale. Letter to the Editor. Pediatrics.
Gina. Doubters Fault Theory Finding Earlier Puberty. New
York Times. 20 February 2001.
Gina. 2 Endocrinology Groups Raise Doubt on Earlier Onset of
Girls' Puberty. New York Times 3 March 2001.