Study: For women, feelings of closeness to a friend improves mood due to increase in progesterone

Women have always known that time spent with a close friend indulging in girl talk really improves our mood, but a University of Michigan study has identified one physical reason: feeling emotionally close to a friend increases levels of progesterone, helping to boost the sense of well-being and reduce stress.

“This study establishes progesterone as a likely part of the neuroendocrine basis of social bonding in humans,” said U-M researcher Stephanie Brown, lead author of a journal article published in the June 2009 issue of Hormones and Behavior. Earlier research has shown that higher levels of progesterone increase the desire to bond with others, but this study is the first to show that bonding with others increases levels of progesterone. The study also links these increases to a greater willingness to help other people, even at our own expense. “It’s important to find the links between biological mechanisms and human social behavior,” said Brown, a faculty associate at the U-M Institute for Social Research (ISR) and an assistant professor of internal medicine at the U-M Medical School. “These links may help us understand why people in close relationships are happier, healthier, and live longer than those who are socially isolated.”

Progesterone can be easily measured with a saliva test, so Brown and her team examined the link between interpersonal closeness and salivary progesterone in 160 female college students. At the start of the study, the researchers measured the levels of progesterone and of the stress hormone cortisol in the women’s saliva. The women were randomly assigned to partners and asked to perform either a task designed to elicit feelings of emotional closeness or a task that was emotionally neutral. After completing the 20-minute tasks, the women played a computerized card game with their partners and had their progesterone and cortisol sampled again.

The progesterone levels of women who had engaged in the emotionally neutral tasks tended to decline, while the progesterone levels of women who engaged in the task designed to elicit closeness either remained the same or increased. The participants’ cortisol levels did not change in a similar way.

Participants returned a week later, and played the computerized card game with their original partners again. Then researchers measured their progesterone and cortisol. Researchers also examined links between progesterone levels and how likely participants said they would be to risk their life for their partner. “During the first phase of the study, we found no evidence of a relationship between progesterone and willingness to sacrifice,” Brown said. “But a week later, increased progesterone predicted an increased willingness to say you would risk your life to help your partner.” According to Brown, the findings are consistent with a new evolutionary theory which argues that the hormonal basis of social bonds enables people to suppress self-interest when necessary in order to promote the well-being of another person, as when taking care of children or helping ailing family members or friends. I can see where that would come into play – if women just went to bed when they were exhausted or wandered off and did whatever they wanted instead of having a natural desire to care for their children, the survival of the next generation might have been more precarious!

“Many of the hormones involved in bonding and helping behavior lead to reductions in stress and anxiety in both humans and other animals. Now we see that higher levels of progesterone may be part of the underlying physiological basis for these effects,” Brown said.

Reference: University of Michigan News Service

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