The study, by researchers at the University of Michigan, examined progesterone levels in the saliva of 160 college students. The women were randomly assigned to partners and asked to perform a task designed to elicit feelings of emotional closeness or a task that was emotionally neutral. After the 20-minute talks the women played a computerized, cooperative game with their partners, then had their progesterone and cortisol sampled again.
The study supports a concept in evolution that is gaining momentum: that the hormonal basis of social bonds enables people to suppress self-interests when necessary to promote the well-being of another person. The research also helps explain why social contact appears to lead to improved health.
"Most of the hormones involved in bonding and helping behavior lead to reductions in stress and anxiety in both humans and other animals," the lead author of the paper, Stephanie Brown, said in a news release. "Now we see that higher levels of progesterone may be part of the underlying physiological basis for these effects."
The study was published in the June issue of the journal Hormones and Behavior.