When the Beatles sang “I get high with a little help from my friends”, they may not have realized just how accurate these lyrics can be. Friendship networks can have an opiate-like capacity to help us resist pain.

In a new study published in Scientific Reports, Oxford University doctoral student Katerina Johnson has explored the neurobiology of friendship networks. She was co-supervised by Professor Robin Dunbar, the inventor of the famous and controversial Dunbar's number, which posits that people on average have 150 friends, of whom a third are considered close.

Johnson's main topic of research is whether neurobiology can explain wide differences in sizes of people's social networks. Dunbar's number is an average, with a huge standard deviation between the people who have small numbers of close friends and the social butterflies who somehow maintain contact with everyone. This topic led her to some unexpected places.

“I was particularly interested in a chemical in the brain called endorphin. Endorphins are part of our pain and pleasure circuitry – they're our body's natural painkillers and also give us feelings of pleasure,” Johnson said in a statement. “Previous studies have suggested endorphins promote social bonding in both humans and other animals. One theory, known as 'the brain opioid theory of social attachment', is that social interactions trigger positive emotions when endorphin binds to opioid receptors in the brain. This gives us that feel-good factor that we get from seeing our friends.”

Since endorphin is a more powerful pain killer than morphine, Johnson tested this theory by comparing the size of 101 18- to 35-year-olds' social networks with how long they could hold a painful position.

Johnson found pain resistance is a significant predictor of the size of a person's social network; the association is strongest with the “outer network layer,” the number of people someone is in contact with monthly, but not on a weekly basis. Essentially, people with more friends have a higher pain tolerance. Unsurprisingly, other factors, such as agreeableness, also influenced numbers of friends, but these were independent of pain tolerance.

“Further research is required to understand the causality of this relationship between pain tolerance and network size,” the paper notes. “It may be that individuals with genetic variants conferring enhanced μ -opioid neurotransmission derive greater reward from social interactions, thereby seeking more company. An alternative, though not mutually exclusive, explanation is that individuals leading lives rich in social interactions may release higher levels of endogenous opioids and/or have elevated receptor expression.”

Johnson found two other intriguing correlations. People who were fitter and described themselves as more stressed both had smaller social networks, despite the fact that fitter people were usually also able to tolerate pain longer.

“It may simply be a question of time,” she said. “However, there may be a more interesting explanation... perhaps some people use exercise as an alternative means to get their 'endorphin rush' rather than socializing.” Larger social networks help people to manage stress better, Johnson added, “or it may be that stress or its causes mean people have less time for social activity, shrinking their network.”