“Anxiety has been with me for as long as I can remember,” explains writer Bella Mackie, 35, who, throughout early adult life, developed a string of rules and avoidance tactics to try and ward off panic attacks, claustrophobia and agoraphobia.

Unfamiliar streets became no-go zones, going into town with its crowds of shoppers was unthinkable, and getting stuck on a stationary Tube train on New Year’s Eve 2000 stopped her from taking the London Underground again for the next 18 years. “I probably felt like that for most of my 20s,” says Mackie, a former features writer for Guardian and Vice.

“It was kind of my default adulthood really, but by the time my marriage ended, I couldn’t even go to the supermarket down the road. I was so used to allowing my mind to dominate everything; it could take me to dark places that I would indulge for hours and hours every day.”

Mackie’s husband told her he was leaving before they’d even celebrated their first wedding anniversary. The break-up was the catalyst for a breakdown so severe that she felt too fearful to leave the house. But it was also a catalyst for change.

Fed up with feeling trapped by anxiety, Mackie decided to do something she hadn’t tried before: Go for a run. “There’s a moment in Catcher In The Rye when Holden Caulfield runs across the school playing fields and explains it away by saying: ‘I don’t even know what I was running for - I guess I just felt like it’,” she says. “I think I just wanted to shut my brain up, and I thought that if I tried to do something physical, like going for a run, that it might just work.”

To her own surprise, it helped. The reason, she believes, is that running and anxiety are kind of similar in their physicality. “You sweat, your heart rate spikes and you feel out of breath. Your stomach churns. Because I was experiencing the familiar symptoms, but in a positive way, I felt like I was able to go a bit further with my running. I never fainted or passed out or freaked out, so I could just keep going into my unsafe areas.”

After that initial night, Mackie says she felt something change. “It became this amazing freeing thing, where I could keep passing those limits and going to scarier places. I couldn’t ignore the anxieties, but I could break out of it for a few minutes per day when I pulled on my trainers.”

Since that first jog down an alleyway at the side of her house, she’s run every day for the past five years, and credits it with helping her to get her back on her feet.

Now, she’s written a book on her experiences, called Jog On: How Running Saved My Life. As well as her own experiences, Mackie cites studies that back her belief in running as a form of self-help. A survey of more than 8,000 people carried out by the Glasgow Caledonian University, looking at whether running can make you happy, found some interesting results. Parkrun participants emerged with an average score of 4.4 (where ‘6’ is extremely happy) compared to the general population, who scored an average 4.

Initial trials in the USA on veterans with post traumatic stress disorder have also found that exercise can bring about a reduction in fear, along with a lessening of physical symptoms, while a study into the effect of running on people with a history of psychosis reported that it can cut the effects by 27%.

Mackie is keen to stress that she doesn’t recommend replacing medication or therapy with running, but that it can be a supplement to traditional forms of mental health treatment.

It’s not just adults that can benefit either; physical exercise can be very useful for children’s mental wellbeing too. One 2017 study in Norway found that moderate to vigorous exercise in six to eight-year-olds meant they were less likely to show symptoms of major depressive disorder two years later.

The study also found that the older children got, the less physical activity they took each day. “Parents don’t imagine that their children will have mental problems that early,” says Mackie. “We think of mental health awareness among teenagers and people in their 20s, and I think it still comes as a shock to parents of younger children. It’s actually quite a normal thing.”

Whatever your age, Mackie says there’s pleasure to be found in what she calls a “runner’s break” - a type of mindful meditation where your mind is completely clear of intrusive thoughts.

“When you’re running, your body takes over and your brain is looking out for the pavement in front of you. It doesn’t really have the chance to bury into the worries and the fears that you might have normally,” she says. “I think that’s probably why most people do it. To make time for an hour out of their frantic lives and to get away from it all.

“It’s so successful in doing that - probably more than a spin class or a gym session where you’re surrounded by people. Not necessarily because it’s solitary, but because you’re literally running away from stuff. It’s a literal thing.”

Mackie did find a happy ending in the romance stakes too. She’s now married to Radio 1 DJ Greg James; they tied the knot in a low-key registry office ceremony, Mackie wearing a yellow silk dress which she described in Vogue as like wearing “particularly chic nightwear”.

That said, getting hitched is not the conclusion of the story: “This book is not about a great love affair gone awry,” Mackie writes. While she still has anxiety, in running she’s found an important coping mechanism, that can help her manage on days when it’s a struggle to leave the house - and that’s the real triumph.

Jog On: How Running Saved My Life by Bella Mackie is published by William Collins, priced £12.99. Available now.