Precocious puberty in girls is a topic currently being researched in
earnest by some of my colleagues here at the Program on Breast Cancer
and Environmental Risk Factors.  I know we've published one recent
newsletter on the topic (written for non-scientists) on the state of
the evidence as it currently stands now. The title of our newsletter
is The Ribbon, and it's available on-line at our web site:
http://www.cfe.cornell.edu/bcerf/

My understanding is that there are at least two competing hypotheses
about causation.  One argues that the cause is dietary exposure to
environmental contaminants that mimic estrogen or otherwise augment
the actions of our sex hormones.  One suspect is phthalates, a group
of plasticizers (chemicals added to plastics to make them pliable),
which are known to be hormonally active inside the human body and to
which all Americans all are presumed to have ongoing exposures.
(Recent CDC study of chemical contaminants in a representative sample
of U.S. children and adults found high levels of phthalates in body
fluids.) There is some very preliminary evidence from Puerto Rico
that girls with premature thelarche (early development of pubic hair
and breasts) have high exposures to phthalates.

Pesticides are another suspect.  There is some very preliminary
evidence from England showing that immigrant girls whose countries of
origin (e.g. India) still use lots of organochlorine pesticides (e.g.
DDT) are experiencing unusually high rates of early puberty.  But
there may be all kinds of other confounding factors here.

The other hypothesis looks toward rising rates of obesity as the
underlying explanation.  Body fat itself produces estrogen, and we
know that girls must attain a certain amount of fat in order to begin
menstruation.  We also know that obesity is rising in tandem with
early puberty.  And we know that heavier girls begin menstruating
earlier.  On the other hand, the issue with precocious puberty is not
early onset of menstruation per se.  Avg. age of first menses is
still about 12.8 years; this hasn't changed much over the past few
decades.  The issue is early onset of public hair, breast
development, and sebaceous gland activity (body odor), changes which
are governed by pituitary and adrenal hormones.

In short, the jury is still out and will be out for a long time on the issue.

To my knowledge, no one has yet published studies that look at
whether fat girls are overrepresented among those experiencing early
puberty, or whether having been formula-fed or breastfed as infants
is predictive of onset of puberty.

I myself get lots of questions from nursing mothers about how best to
store breast milk and what kind of bottles to use that would minimize
phthalate exposure.  I have no information on this.
--
--

Sandra Steingraber, Ph.D.
Visiting Assistant Professor
Program on Breast Cancer and Environmental Risk Factors
110 Rice Hall
Cornell University
Ithaca, NY  14853
[log in to unmask]
www.steingraber.com

             ***********************************************
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(TM)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html