Darling buds: how best friends keep us healthy and happy

“We met when we were five. I don’t know how I would have managed without her.” As children, Barbara Kastelein, from Ashford in Kent, and her best friend, nicknamed “Tulip”, both had alcoholic fathers. Their friendship was an escape from unhappy homes.

The best friends are now both 55 and their relationship is as solid as ever. Barbara says they are more like sisters – and still there for each other during tough times. When Barbara’s father died, Tulip drove for hours to be at the funeral and to help Barbara empty her father’s flat. “I can’t imagine life without her,” says Barbara. “She is my guardian angel.”

But not all best friendships last. Minreet Kaur, 41, from Hayes, met her best friend when she landed her first job after university. “I trusted her instantly, and she did me. We could talk about anything and always had each other’s back. She even supported me through my divorce. I couldn’t see life without her.”

As time went by, Minreet immersed herself in her career while her best friend settled down and had a family. “We found we were leading different lives,” she says. “We don’t keep in touch. I’ve never had such a close friendship since. I miss her. Everyone needs a best friend.”

Some of us have a single best friendship that spans our lifetime. We call them on a whim, we trust them completely, they are there for us, and us for them, without question. They are more like family. But, for adults, making friends can be hard. Scientists say it can take more than 200 hours to become close enough to someone to share a real emotional connection. But what if we don’t have a best friend? If we flit in and out of friendships or have no close friends at all – should we be worried?

The physiology of best friends

We gravitate towards people who are similar to ourselves. Homophily is the concept that similarity makes social connection easier. Now, research has shown that close friends resemble each other not just in manner and appearance, but physiologically too.

Scientists at the University of California scanned the brains of a group of students as they watched a series of short videos and found that those who were close showed incredibly similar neural responses. The areas of the brain that responded similarly included those associated with motivation, learning, processing, memory, empathy, and generally making sense of things. The findings suggest we choose friends who interpret and react to the world in a similar way to ourselves.

Dr Anna Machin, author of Why We Love: The New Science Behind Our Closest Relationships, is an evolutionary anthropologist who specialises in dyadic relationships – the closeness between two people – whether that’s a parent and child, lovers or best friends. “When we’re with someone we love, we experience a thing called biobehavioral synchrony,” she says.

She describes how, when two people are tightly bonded, they mirror each other’s behaviour. They use the same gestures. They pick up the same tone of voice or use the same phraseology. Best friends’ physiology comes into synchrony too – the rhythm of their hearts, body temperature and hormonal responses. Look inside the brain and you’d see synchrony, says Machin, in the gamma waves – the higher cognitive functioning parts of the brain.

The London commuter problem

So, are we hardwired to seek out a best-friend relationship? Robin Dunbar, emeritus professor of evolutionary psychology at Oxford University, studies the connection between behaviour, cognition and neuroendocrinology – the brain’s regulation of hormonal activity in the body.

The maximum number of friendships humans are able to maintain, says Dunbar, is 150. “Dunbar’s number” harks back to the size of prehistoric hunter-gatherer communities but is also true of modern society. However, it’s not always plain sailing when you live in a large group. “Group living can be a major problem for mammals, especially primates. The bigger the group, the more stresses you suffer.”

Dunbar describes what he calls the “London commuter problem”, the pressure of living in cramped conditions with other people. It is your closest friends, he says, that make social living possible by keeping others at bay.

“Friendships vary in quality and make up a series of layers, or circles. You have an inner core of five and, within that, a layer of 1.5. These are your most intimate friends or your romantic partner. Your inner circle – and within that your best friend for ever – provides a hugely important buffer against the stresses of living in social groups.”

The reason the number of people in your innermost circle of friends is 1.5, explains Dunbar, is that for men it tends to be their romantic partner, whereas for women it’s their romantic partner plus a close (usually) female friend.

The best antidepressant you can get

Dunbar describes the physical benefits of friendship – the calming effect you feel as endorphins are released on social interaction with your “bestie”, as well as the positive effects such close bonds have on the immune system. “A connection of this kind is the best antidepressant you can get,” says Dunbar.

Close relationships have been shown to result in lifelong physical and mental health benefits. Research shows people with good social bonds are happier, live longer and have better reproductive health. They are less likely to suffer illness and recover more quickly. They can cope better with stress, and there is less risk of developing addictions or psychopathology.

A meta-study of 149 studies found that bonds with close friends could even be more important to your health than losing weight or exercising. In fact, according to a US survey of 20,000 people, not having close relationships can be as bad for your health as smoking 15 cigarettes a day.

A mechanism for survival

“At the basic level, friends are a mechanism for survival,” says Machin, “but what’s really interesting about friendship, particularly female friendship, is how we often underestimate the importance of that friendship in our lives. We usually put romantic relationships at the top, then maybe your mum and dad, then friends are down here somewhere,” Machin gestures towards the floor, “but actually, for many women, the critical relationship in life is their best friend.”

Women, she says, are often more emotionally intimate with their best female friend than they are with their romantic partner. They share their deepest, darkest emotional fears and allow themselves to be more vulnerable in front of their best friend than when they are with their partner.

“Women get a really important input from their female friends in terms of their mental wellbeing. If we look at a man’s brain when he’s having deep and meaningful conversation with his closest friend, we see his amygdala – the brain’s fear and risk sensor – fire up, so he’s finding it quite uncomfortable.

“In a woman’s brain, a similar conversation with a best friend results in reward chemicals, an increase in oxytocin, a real sense of relaxation – it’s all amazing, it’s a really brilliant experience.”

Friendships v acquaintanceships

So if we don’t have a best friend, are we broken? “Absolutely not!” says Dr Miriam Kirmayer, a clinical psychologist who specialises in friendship. “Each of our relationships help us meet our need to feel that sense of connection and belonging. This is true of our closest friendships, our acquaintanceships – even our moments of connection with strangers.”

Related: Friends by Robin Dunbar review – how important are your pals?

Kirmayer says it’s not the label that’s important but that our friendships are reciprocal. Research suggests that up to half of our friendships are actually unreciprocated. “When we feel chosen, that is, that the people we choose are choosing us in return, this is paramount. Healthy close friendships are based on balance and reciprocity.”

According to the brain opioid theory of social attachment, social interactions trigger positive emotions when endorphins bind to opioid receptors in the brain. This gives us that feelgood factor that we get from seeing our friends.

“Lots of people I’ve interviewed say they felt an absolute high after spending time with a best friend, which carried them through the whole of the next day,” says Machin. Thinking about the neurochemistry explains how during lockdown many people were, in effect, suffering from withdrawal.

#justhangingwithmybestie

Technology has made it easier to connect with friends – and it has become the norm to publicise our friendships. There are currently almost 69m Instagram posts tagged #bestfriends and the hashtag #IBF (internet best friend) recently clocked more than 25m views on TikTok.

But how does this modern manifestation of best-friendship interact with life offline? Social media interactions have been shown to increase closeness between friends who also interact offline, yet social media use has been shown to displace time spent on face-to-face interactions.

“You can maintain real friendships online. Social media simply provides a medium of communication,” says Dunbar. “However, [communicating online] is not as gratifying as face-to-face. It only slows the rate of decay of relationships. It won’t stop them decaying eventually.”

Machin adds: “It is much harder to maintain relationships online because of the reduction – if not complete lack – of neurochemical release. And there is certainly no biobehavioral synchrony.”

Absolute profound love

When it comes to the complexity of social bonding, nothing compares to human friendship – and your best friend is the most important of all. “Friendship infiltrates every aspect of our lives, every aspect of our physiology,” says Machin. “It’s astonishing how complicated it is.”

At its most basic level, says Machin, friendship is biological bribery. It’s a set of neurochemicals that motivate and reward you for forming and maintaining relationships. It’s a mechanism that has evolved to make sure that you invest in the relationships that are critical to your survival and the survival of the species.

It’s through biobehavioral synchrony that we feel that profound connection. We see this in romantic relationships, we see it in relationships between parents and children, and we see it in best friends. While we often look for desirable practical qualities in a romantic partner – would they be a good parent to my children? Do we share similar goals in life? – our priorities for a best friend differ.

“In best friendships, we know that the parties are more relaxed, more open with each other,” says Machin, “because they are not always having to remain attractive for their partner.” A best friendship is all about shared humour, values and support. You can live on opposite sides of the Earth and still feel that closeness with your one special friend.

“It’s as if every sinew in your body is engaged in having a relationship with that person,” says Machin. “That for me sums up how important best friends are. Evolution has seen fit to engage every mechanism in your body – the behavioural, the physiological, the neurological – to make sure that you’re as tightly bonded to this person as you possibly can be. We wouldn’t have evolved this way if those relationships weren’t critical for survival.”