Contact: Andrea Estrada
University of California â€“ Santa Barbara
(Santa Barbara, Calif.) Feeling frisky? If so, chances are greater your estrogen level and, perhaps, fertility are hitting their monthly peak. If not, youâ€™re more likely experiencing a profusion of desire-deadening progesterone, and the less fertile time in your cycle. Oh, the power of hormones.
Researchers have long suspected a correlation between hormone levels and libido, but now scientists at UC Santa Barbara, led by James Roney, a professor in the Department of Psychological and Brain Sciences, have actually demonstrated hormonal predictors for sexual desire. Their findings appear in the current issue of the journal Hormones and Behavior.
â€œWe found two hormonal signals that had opposite effects on sexual motivation,â€ said Roney, the articleâ€™s lead author. â€œEstrogen was having a positive effect, but with a two-day lag. Progesterone was having a persistent negative effect, both for current day, day before, and two days earlier.â€ When hormone levels and sexual desire were factored against the menstrual cycles of test subjects in this case, undergraduate students the researchers saw a measurable increase in progesterone levels at the same time the subjects noted decreases in sexual motivation. Progesterone, the researchers say, is mediating this drop in desire from the fertile window to the luteal phase the second half of the menstrual cycle.
â€œProgesterone acting as a potential stop signal within cycles is a novel finding in humans,â€ noted Roney. â€œWe know in rhesus monkeys there is a strong negative correlation with progesterone and a positive correlation with estrogen. The patterns are actually comparable to what you see in non-human primates, but hadnâ€™t been shown in humans.â€
The researchersâ€™ findings have potential implications on the treatment of low sexual desire and how hormone replacement trials are done. â€œWeâ€™re not controlling hormones the way they do in the hormone replacement literature, so, in a sense, that literature is more directly applicable in terms of medical applications,â€ said Roney. â€œBut in the long run, it would be good to have a model of the combination of signals that operates in the natural cycle. The way hormone replacement trials are done now, thereâ€™s no model of the natural signals, so theyâ€™re sort of random letâ€™s give estrogen, letâ€™s give testosterone, letâ€™s combine them this way or that way.â€
Roney noted that his findings donâ€™t present a full model, and heâ€™d like to replicate his results with women of different age groups. â€œUndergraduates might be unique for a lot of reasons,â€ he said. â€œTheir hormone levels tend to be a bit different from those of women even just a little bit older. And married women in their 30?s are likely to be more consistently sexually active, and that might change the patterns in some ways. They also tend to have higher hormone secretion and more regular cycles than younger women,â€ he said
Eventually, Roney continued, the goal would be to have a better model of the signals in a natural cycle that might then inform medical research.
Another interesting finding, according to Roney, was the impact or lack thereof of testosterone on the womenâ€™s sexual motivation. â€œThereâ€™s a common belief in the medical literature that testosterone is the main regulator of womenâ€™s libido,â€ he explained. â€œDoctors tend to believe that, though the evidence isnâ€™t that strong in humans. In the natural cycles, we werenâ€™t finding effects of testosterone. It wasnâ€™t significantly predicting outcomes.â€
Roney doesnâ€™t deny that testosterone does seem to have a positive effect in hormone replacement therapy, but suggests the effects may be pharmacological. â€œTestosterone has those effects if you inject it externally in women who are menopausal, and there are a lot of reasons that might be the case,â€ he said. â€œFor example, testosterone can be converted to estrogen through a particular enzyme. If you inject menopausal women with testosterone, it might be acting as a device thatâ€™s delivering estrogen to the target cells. So the fact that it works doesnâ€™t necessarily mean itâ€™s an important signal in the natural cycle.â€
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