Hormonally Active Agents In The Environment
Committee
on Hormonally Active Agents in the Environment
Board
on Environmental Studies and Toxicology
Commission
on Life Sciences
National
Research Council
National
Academy Press, Washington D.C. 1999, page 73.
Phytoestrogens
"The recent
practice of feeding infants soy-based formula has raised concerns with
regard to the long-term health effects of exposure during
development..."
"The
concentration of soy phytoestrogens that inhibited thyroid hormone
biosynthesis is within the range of exposure of infants maintained on
soy formula."
"...exposure
of plant estrogens found in wood..." Note that these are the same as
those being added to margarines.
Human and
animal exposures to the phytoestrogens, particularly isoflavones, can
be very high, because these compounds are found in many foods.
Genistein, daidzein, formononetin, and equol are all present in clover.
Infertility in sheep, “clover disease”, has been traced to
isoflavone concentrations as high as 5% of the dried weight of clover
(Verdeal and Ryan 1979).
The recent
practice of feeding infants soy-based formula has raised concerns with
regard to the long-term health effects of exposure during development
(Setchell et al. 1997; Irvine et al. 1998). For example, it has been
recognized for some time that feeding infants soy-based formula was
associated with goiter (thyroid enlargement associated with thyroid
hormone deficiency) in animals and human infants (Shepherd et al.
1960). One mechanism by which isoflavonoids, such as genistein, reduce
thyroid hormone concentrations and result in goiter is by inhibiting
thyroid peroxidase activity; this enzyme catalyzes thyroid hormone
biosynthesis (Divi and Doerge 1996). The concentration of soy
phytoestrogens that inhibited thyroid hormone biosynthesis is within
the range of exposure of infants maintained on soy formula. Soy-based
formulas contained isoflavones at 32-47mg/mL, which corresponded to a
daily exposure to total isoflavones of 4.5-8.0 mg/kg of body weight per
day for a 4-mo-old infant. That concentration is 6- to 11-fold higher
than concentrations known to cause hormonal effects in adults. (Divi et
al. 1997; Setchell et al. 1997). In a study by Irvine et al. (1998),
the phytoestrogen content of soy-based formulas and cereals were
compared with dairy-based formulas and human breast milk. Again, the
infants received approximately 3 mg/kg of body weight per day from the
soy-based formula, but a single daily serving of infant cereal could
increase the isoflavone intake by more than 25%. Dairy-based formula
and human breast milk contained isoflavones below the limit of
detection. Human breast milk had undetectable concentrations of
phytoestrogens regardless of the diet of the mother, including women
who were vegetarians and consumed greater than 50 g of soy products in
a 48-hr period before sampling.
Potential
exposure to plant estrogens found in wood has been assessed by various
in vitro and in vivo bioassays. Wood-derived estrogens, such as
beta-sitosterol, could represent environmental hormone exposures,
particularly from pulp and paper mill effluents, downstream of
wood-processing facilities, Mellanen et al. (1996) used two
breast-cancer cell lines in vitro (MCF7 and T-47D) and expression of
the vitellogenin gene in rainbow-trout livers to estimate estrogenic
activity of wood-derived compounds. Some compounds, such as
beta-sitosterol, were estrogenic in human and fish bioassays, but some
phytoestrogens, such as betulin and pinosylvin were estrogenic only in
humans.
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