The "cuddle hormone" oxytocin gets all the attention, but a new study finds that other chemicals in the brain may play even bigger roles in people's interactions with others.
In the study, researchers looked at people's genes for six different "social neuropeptides" — chemicals in the brain that are involved with social interactions — and found that two have particularly large effects on relationships.
"There are a number of chemicals in the brain that play an important role in predisposing us to behave in particular ways," said senior study author Robin Dunbar, a professor of evolutionary psychology at the University of Oxford in England. [11 Interesting Effects of Oxytocin]
Dopamine, for example, is sometimes called the "happy" chemical, Dunbar said. And endorphins "make [people] relaxed and [lead to them] feeling warm towards others."
Indeed, the new study showed that these two chemicals — endorphins and dopamine — "play an especially important role in facilitating friendships and social networks," he said.
The study, which was published May 1 in the journal Proceedings of the National Academy of Sciences, is one of the first studies to look at how a group of neuropeptides interact.
"Up until now, most of the studies in this area have focused on just one neuropeptide, oxytocin," Dunbar told Live Science. But although the new study found that oxytocin does play "some limited role," notably in romantic relationships, "in fact, it plays a much less important role than endorphins and dopamine" in people's social lives more broadly, Dunbar said.
In the study, the researchers tested the DNA of more than 750 British adults and looked for tiny variations in nine genes that are associated with the six social neuropeptides: oxytocin, dopamine, endorphins, vasopressin, serotonin and testosterone.
The people in the study also filled out questionnaires about their social lives. The researchers looked for links between the participants' versions of those nine genes and their behaviors in three areas: the individuals' predisposition to being friendly and helpful, the quality of their one-on-one relationships (including romantic relationships), and how well they were connected with their extended social networks, according to the study.
Dunbar noted that it is particularly important to study the third area, the extended social network. "The number of friends we have has massive effects on our health, happiness and well-being," he said. [7 Ways Friendships Are Great for Your Heatlh]
The researchers found that dopamine played a big role in this third area, Dunbar said.
The researchers also found that endorphins played a strong role in a person's social predisposition, and that oxytocin was involved only in romantic relationships, he said. But even its role in romantic relationships can be by overpowered by endorphins in some respects, he added.
Although endorphins were strongly linked to predisposition to being friendly and helpful, and dopamine was linked to how well a person was connected to his or her social network, these neuropeptides "influence all three [areas] and are thus broadly more important to how our social life works," Dunbar said. In addition, "endorphins and dopamine work in tandem with each other," he said.
The three other neuropeptides (vasopressin, serotonin and testosterone) weren't found to play large roles in social interactions, the study said.
Originally published on Live Science.