October 8, 2001
Estrogen supplements may decrease female sex drive
By Poul Olson
Phytoestrogen supplements, an increasingly popular soy-derived alternative
to estrogen-replacement therapy, do not produce the same molecular and
behavioral effects on the brain as naturally occurring estrogen, according
to a Center for Behavioral Neuroscience (CBN) study that appeared in the
Whats more, when administered to female rats in combination with
synthetic estrogen, phytoestrogens actually interfere with estrogens
ability to promote sexual receptivity.
Produced by plants, phytoestrogens have been touted in recent years as
helping to prevent heart disease and cancer and ameliorate the effects
of menopause such as hot flashes and mood swings. The estrogen-like molecules
reportedly produce effects similar to estrogen in reproductive tissues.
For post-menopausal women, estrogen replacement therapy (ERT) has been
shown to enhance mood and cognitive abilities. Scientists, however, have
not examined whether phytoestrogens have the same estrogen-like effects
in the brain as they do in the body.
In the study led by CBN scientist Heather Patisaul, a store-bought phytoestrogen
supplement was administered to female rats at a dose relative to what
a woman might consume on a daily basis. Using molecular techniques to
quantify gene expression in the brain, Patisaul and her team compared
the effects of phytoestrogens and estradiol, a synthetic estrogen, on
the regulation of two genes known to be controlled by estrogen receptors
alpha and beta. The scientists found that phytoestrogens did not act in
a similar manner as estrogen in the brain.
At the molecular level, the compounds actually did the opposite
of what estrogen normally does, Patisaul said. They were anti-estrogenic
for both estrogen receptor alpha- and beta-dependent gene expression.
What surprised the CBN team even more was the effect of phytoestrogens
on sexual behavior. When administered in combination with estradiol, phytoestrogens
significantly reduced the propensity of the female rats to assume a sexually
receptive posture called lordosis.
Phytoestrogens clearly inhibit estrogens ability to make
the rats sexually receptive, Patisaul said, noting that sexual behavior
in female rats is dependent on circulating estrogen concentrations. Its
possible that phytoestrogens interfere with oxytocin dependent
The estrogen alpha receptor regulates oxytocin receptor expressiona
key hormone involved in social behavior and reproduction.
Patisaul and her team plan to duplicate their study with a particular
phytoestrogen, Genistein, found in soy isoflavone supplements and well
studied as a cancer suppressant. The CBN scientists want to determine
whether a single phytoestrogen or a combination of the compounds is responsible
for the observed molecular and behavioral changes.
Given the unexpected outcome of their study, Patisaul and her colleagues
offered a cautious note to women who use phytoestrogens: Our study
shows that we cant assume that soy supplements have the same effects
as estrogen replacement therapy, Patisaul said. When it comes
to cognitive function, phytoestrogens may not be an appropriate substitute
for estrogen replacement therapy.
Patisaul co-authored the paper with Marietta Dindo, Patricia Whitten and Larry Young, and the study was funded by a $30,000 CBN venture grant.