New University of Michigan psychology research suggests that the sex hormone estrogen may be for women what testosterone is for men: The fuel of power.

Until recently, some researchers doubted whether women had a biologically anchored need for dominance.

"Women have long been overlooked in biological research on dominance," said psychology researcher Steven Stanton. "Using a male model, the small body of existing research has struggled to link testosterone to dominance motivation and behavior in women.

"However, estrogen is very behaviorally potent and is actually a close hormonal relative to testosterone. In female mammals, estrogen has been tied to dominance, but there has been scant research examining the behavioral roles of estrogen in women."

The study by Oliver Shultheiss, a psychology professor who directs the Human Motivation & Affective Neuroscience Lab, and Stanton, who is completing doctoral work at the lab, was recently detailed in the journal Hormones and Behavior.

Schultheiss and Stanton measured women's power needs and then assessed salivary estrogen levels both before and after they entered a one-on-one dominance contest.

The researchers found that even before women got involved in the contest, higher power motivation was associated with higher levels of estrogen.

Winners of the contest showed even further increases in estrogen after the contest, but only if they had a strong need for power. Notably, this increase could still be detected one day after the contest was over.

In contrast, power-motivated losers showed a post-contest decrease in estrogen. These effects were not observed among women who did not possess a strong need for power.

"Our findings perfectly parallel what we have observed for power motivation and testosterone in men," Schultheiss said. "In men, power motivation is associated with heightened levels of testosterone, particularly after a contest victory. In women, estrogen appears to be the critical hormone for power motivation."