People with a larger circle of friends are better able to tolerate pain, according to research into the pain thresholds and social networks of volunteers.

The link is thought to be down a system in the brain that involves endorphins: potent pain-killing chemicals produced by the body that also trigger a sense of wellbeing.

“At an equivalent dose, endorphins have been shown to be stronger than morphine,” said Katerina Johnson, a doctoral student at the University of Oxford, who co-authored the research. 

Writing in the journal Scientific Reports, Johnson and Robin Dunbar, professor of evolutionary psychology at the University of Oxford, sought to probe the theory that the brain’s endorphin system might have evolved to not only handle our response to physical discomfort, but influence our experience of pleasure from social interactions too. “Social behaviour and being attached to other individuals is really important for our survival - whether that is staying close to our parents, or our offspring or cooperating with others to find food or to help defend ourselves,” said Johnson.

To test the link, the authors examined both the social networks and pain thresholds of 101 adults aged between 18 and 34. Each participant was asked to complete a questionnaire, designed to quiz them on friends they contacted once a week and those they got in touch with once a month. The personality of each participant was probed, looking at traits such as “agreeableness”; they were also asked to rate their fitness and stress levels.

As greater endorphin activity in the brain is linked to higher pain tolerance, each participant was asked to squat with their back against a wall and their knees at right-angles to their body - a simple but uncomfortable exercise. They were asked to stay in the position for as long as they could bear it, providing researchers with an indirect method of gauging endorphin activity in the brain.

The researchers found that for both men and women, larger social networks were linked to a greater pain tolerance. What’s more, it was the number of friends contacted on a monthly - rather than weekly - basis that appeared to be the most important factor. “This relationship with brain endorphin activity may only be important when it comes to the limits of the number of close social bonds that we can maintain since nearly all of us have some friends and family that we rely on in times of need,” said Johnson.

From the results, she added, when stress, fitness and agreeableness are controlled for, an increase from seven to 12 friends in this second layer of contacts is predicted to boost tolerance in the pain test from one minute to four minutes on average. But, said Johnson, it was not clear whether the link was down to greater social activity boosting the release of endorphins and thereby dampening the experience of pain, or whether people with a more active endorphin system - and hence higher pain tolerance - experience a greater reward from social activity and hence surround themselves with more friends. 

Intriguingly, while participants who reported higher levels of fitness were able to endure the pain test for longer, the researchers discovered that these participants generally had smaller friendship groups.

“The obvious answer is that it is a question of time - if you are in the gym all the time you are going to have less time to socialise with your friends,” said Johnson. But, she adds, there is another possible explanation. “Both exercise and socialising trigger the endorphin system,” she said, adding that those who experience an endorphin rush from the gym might not feel the need to seek a similar feeling from mixing with friends.

Those who reported high levels of stress were also found to have fewer friends, although there was little correlation to pain tolerance. But it is not clear whether stress itself hinders people from forming and maintaining relationships, or whether by having more friendships others were better able to cope with life’s pressures. “It is probably a combination of the two,” said Johnson.

While the research supports previous evidence that endorphin activity in the brain might be linked to social interactions, Johnson added that it is not yet clear what causes the differences between individuals. One possible explanation is that genetic variations can affect the density of endorphin receptors in the brain. “If you have more endorphin receptors this may predispose you to being more sociable,” she said.

Lauri Nummenmaa, from Aalto University in Finland, believes the study raises new avenues of research, adding that one experiment would be to probe whether the activity of the endorphin system increases when people socialise. “Those kind of experiments are needed to really nail down what is going on,” he said.

Robert R. Provine, professor of psychology at the University of Maryland, and author of Curious Behavior: Yawning, Laughing, Hiccuping, and Beyond, believes it is important to further tease apart different ways in which social interactions might be linked to wellbeing.

“If experiencing chronic pain, should we join a choir, march off with an army, or spend more time with friends? All may have a positive effect, but the challenge is in establishing the mechanism through which such social interventions work,” he said. “Is it through release of the brain’s own opioids, as suggested by Johnson and Dunbar, cognitive mechanisms of attention or distraction, a combination of all three, or some other mechanism?”