When you are a child in the playground it is pretty simple, but “Do you want to be my friend?” isn’t a line you hear from adults. Teenage years are filled with friendships easily made (and some easily forgotten), when you are feeling keen, sociable and energetic. Then there are engagements, marriage, relocation, career changes, families: life comes calling with its multiple demands, and friendships evolve as a result. I have been happy to see my friends move through these huge life moments, but as much as I value my friendships, I have found myself lonely at times. Some friends are physically far away, while others are time-poor and, with the best will in the world, it isn’t simple to see each other as often as we would like.

According to a recent study by the Red Cross in partnership with Co-op, more than nine million adults in the UK are often or always lonely. We are facing a loneliness epidemic, with Theresa May taking the step earlier this year of appointing Tracey Crouch as what some have dubbed the “minister for loneliness” to try to tackle the issue.

Loneliness is something we all feel at times and to varying degrees, but it can also be something that we feel uneasy about admitting to.

Another study, published in the journal Personal Relationships, found that investing in close relationships was associated with better health, happiness and wellbeing in adulthood.

Still, making friends as an adult can be hard, and takes time – last week a study from the University of Kansas found that two people need to spend 90 hours together to become friends, or 200 hours to qualify as close friends.

Clinical psychologist Linda Blair agrees that this can be difficult to achieve: “Usually the basis of making a friend is a shared experience.” These are often in abundance in our earlier years, but once those easy opportunities are gone, you can forget that the initial basis for a friendship is to have a similar passion or interest. Joining a group or class based on something you really love, or volunteering for something you care about, can be a great first step for finding friendships, she advises.

Although it can be tricky and nerve-racking, making new friends as an adult can also be rewarding: a message Jacqueline Thomas, 52, is keen to share. Moving to the Warwickshire village of Bulkington in 2015 with her partner David, who is soon to retire, she relished the opportunity to start anew.

“We’ve had to start from scratch because we didn’t know anybody here. Our kids have grown up, so we were looking at a slightly quieter life, but it’s actually turned out to be busier than before,” she says.

Jacqueline started by introducing herself to her neighbours. She credits signing up to a variety of classes and groups at the village hall as the catalyst for her new friendships. She joined the WI hesitantly, worried it would be “all jam and Jerusalem, and I’d be the youngest person there”. But she now says it was one of the best decisions of her life.

Don’t be afraid to try something new, she stresses. A lifelong wheelchair user, Jacqueline was intrigued by a poster in the village hall advertising an adapted martial arts class. Having gone along with some doubts, she was surprised to find how much she enjoyed it. Encouraged by her teacher, Carl Hodgetts, who in 2006 became the first wheelchair-using kickboxing instructor in the UK, she now proudly holds a white belt in Shiying Do adapted martial art. “It just takes one leap of faith. Even if you’re absolutely terrified, do it,” she says, adding: “Even I’m a bit shocked about the martial arts, though.”

Over the past couple of years, and nearing 30, I made a conscious effort to make friends. Not to replace old ones, but to make new connections. Friendships, says Blair, are “like an onion. There’s all these layers of friends and the inner layer are your best friends – you probably only have two or three in your whole life.” You might not gain a new best friend, but finding friends for different interests in your life, at different stages, can be a positive.

A personal success story came from a friend’s wedding last summer. Rebecca and I bonded over our rumbling bellies as we awaited the bride’s entrance. It turned out we lived near each other in London and had gone to the same school in Dorset (albeit in different years, which when you’re a child makes a crucial difference). We discussed travel, food and summer plans, but I wasn’t sure our newfound friendship would exist outside the tipsy haze of a wedding celebration. But I had resolved not to let these moments slip away and took her number. Fast forward to a meetup in a bar in central London. I had fretted about what to wear, whether she would recognise me and if there would be awkward silences; but we are now firm friends, exploring the capital and taking it in turns to suggest somewhere new.

Joining local running and cycling groups has also been a positive step. It is an excellent way to meet people in the area. Pete McLeod, 25, a fellow athletics fan and member of my track and field club, Hercules Wimbledon, agrees. After finishing his master’s at Loughborough University, he moved to Wimbledon for his first job and joined the club to keep fit. Making new friends has been a bonus: “It’s really rewarding. You get to practise something you enjoy but also have the opportunity to meet new people.”

Pete made a New Year resolution in 2015 to push himself out of his comfort zone and speak to people more: “The club was a good opportunity to put that into practice … when people aren’t out of breath.” He counts some members of the sprinting group as very good friends now, with the japes and conversations flowing over into tennis matches or walks and coffee at the weekend.

It is important to be proactive, says Juliana Nabinger, 42, who moved from Brazil to Chile with her husband and two young children three years ago. “Don’t sit and wait – it won’t happen. You have to actively search for new friends.” Now fluent in Spanish, she says that when she first moved she would use the few words she knew to ask questions while waiting for her children to finish at school, even when she knew the answers: “At first it was difficult because I really started to miss my friends and adult conversation, but the kids kept me busy and, through them, I made friends.”

Now, via a Facebook group of English-speaking mums and her Spanish conversations at the school gates, she has a solid group of local and expat friends. “The best thing is, you’re older and you don’t judge people,” she says. The worst? “Sometimes people don’t understand your feelings or choices because they don’t know everything. They only have parts of a puzzle.”

Friendships can also come from the most unexpected places. Moving from Eday, a small island in Orkney, with a community of about 140 people, to mainland Orkney, Stephen Walters, 43, and his family went from knowing almost everyone to not knowing anyone socially. His wife, Ronie, started the UK’s most northerly roller derby league, the Orkney ViQueens. Initially, Stephen joined to train as a referee and was the only man there, but he went on to became a coach despite having little previous experience on skates. Within a year he had an abundance of friends of all ages, he says.

Roller derby’s ethos of inclusion and equality has been a big attraction for him: “I have bipolar disorder and there are a couple of others with similar issues. You can tell when somebody is not quite their usual self and people generally look out for each other, which is really nice.”

Not having been involved much in a sport before, he admits he was concerned it would be difficult at his age, but now urges others to give it a try: “Go out and try some activities you’re interested in and talk to people. If it doesn’t work, try another one.”

Embarking on friendships as an adult can be terrifying, exciting, rewarding and challenging. Nothing can replace the special connections you have with those who have known you over the years, but taking that leap of faith Jacqueline mentioned can reinvigorate and get the ball rolling. Before rushing off to her afternoon martial arts class, she imparts some simple but effective advice: when it comes to making friends, “Don’t be afraid of being scared. Do it anyway.”

Linda Blair’s friendship tips

Build your self-confidence

Liking yourself before going off in search of friends is an important step to building healthy relationships. “Think about what you like about yourself. When you’re comfortable with yourself, it shines out of you.”

Find something you feel passionate about

Join a language class if you love languages or volunteer outdoors if you love nature. “That’s where you’ll find friendships.”

Put yourself out there

Remember, nothing ventured, nothing gained. “It isn’t that you lose if you meet someone and it doesn’t fit for a friendship. That’s not losing, that’s having tried.”

Meet in a neutral place

Once you have taken the first step and are moving on to meeting outside the initial environment where you made a connection, chose a neutral public space. This can lessen the pressures that, say, hosting at home can bring, and give you time to focus on each other.

Ask questions

“If you want to be popular, ask people about themselves and listen sincerely when they answer. A good listener is rare these days. It is the best passport you could possibly have to friendship.”

Don’t expect too much

A common mistake is expecting too much from one person. It is more realistic and healthier to have a variety of friends for different reasons.