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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 July Endocrinology.

What’s more, when administered to female rats in combination with synthetic estrogen, phytoestrogens actually interfere with estrogen’s 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 estrogen’s ability to make the rats sexually receptive,” Patisaul said, noting that sexual behavior in female rats is dependent on circulating estrogen concentrations. “It’s possible that phytoestrogens interfere with oxytocin dependent

The estrogen alpha receptor regulates oxytocin receptor expression—a 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 can’t 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.


Back to Emory Report October 8, 2001