Women More Likely to Initiate Sexual Advances During Most Fertile Peak of Month

A new study among UCSB researchers shows that women are more likely to initiate sexual advances during their peak fertility period of the month.

Researchers have long determined a strong connection between libido and hormone levels, but now lead scientist of the study, James Roney, a professor in the Department of Psychological and Brain Sciences, has actually demonstrated hormonal predictors for sexual desire.

"We found two hormonal signals that had opposite effects on sexual motivation," said Roney, according to a press release. "Estrogen 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."

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.

"Progesterone acting as a potential stop signal within cycles is a novel finding in humans," noted Roney. "We 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 hadn't been shown in humans."

The researchers' findings have potential implications on the treatment of low sexual desire and how hormone replacement trials are done.

"We'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," said Roney. "But 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, there's no model of the natural signals, so they're sort of random -- let's give estrogen, let's give testosterone, let's combine them this way or that way."

Their findings appear in the current issue of the journal Hormones and Behavior.