“I was particularly interested in a chemical in the brain called endorphin. Endorphins are part of our pain and pleasure circuitry – they are our body’s natural painkillers and also give us feelings of pleasure,” said Katerina Johnson from University of Oxford in the UK.
One theory, called the brain opioid theory of social attachment, is that social interactions trigger positive emotions when endorphin binds to opioid receptors in brain.
This gives us that feel-good factor that we get from seeing our friends, said Johnson.
“To test this theory, we relied on the fact that endorphin has a powerful pain-killing effect – stronger even than morphine,” she added.
Researchers used pain tolerance as a way to assess the brain’s endorphin activity. If the theory was correct, people with larger social networks would have higher pain tolerance, and this was what their study found.
“These results are also interesting because recent research suggests that the endorphin system may be disrupted in psychological disorders such as depression,” said Johnson.
“This may be part of the reason why depressed people often suffer from a lack of pleasure and become socially withdrawn,” she said.
Both fitter people and those with higher reported stress levels tended to have smaller social networks, researchers said.
“It may simply be a question of time individuals that spend more time exercising have less time to see their friends,” said Johnson.
“However, there may be a more interesting explanation – since both physical and social activities promote endorphin release, perhaps some people use exercise as an alternative means to get their ‘endorphin rush’ rather than socialising,” she said.
The finding relating to stress may indicate that larger social networks help people to manage stress better, or it may be that stress or its causes mean people have less time for social activity, shrinking their network.
Participants were asked to complete a questionnaire relating to the two innermost social network layers, as well as providing information on lifestyle and personality.
They then performed a test which involved squatting against the wall with knees at a 90 degree angle and a straight back (the wall sit test), researchers said.
They were asked to hold this position and endure the discomfort for as long as possible.
Even when allowing for differences in individual fitness, researchers found that people who could endure this pain test for longer, also tended to have larger social networks.
The findings were published in the journal Scientific Reports.