Loneliness is a stealthy bastard. It can settle in on your soul without you even noticing, until the texture of the words appear on your tongue one day: “I’m lonely.” It’s a hollow melancholy that wraps itself around your heart and stays there, whispering fear of social rejection in your ear and growing stronger, feeding on your insecurities.

As much as we may like to think it is a symptom of old age – the kind of thing that only happens when everyone you loved is laying supine six feet under – it can touch anyone from any age or demographic. Loneliness does not discriminate; it is so prolific that you could say it is an inevitable quirk of human existence. In loneliness, my friend, you are not alone: a Red Cross study revealed that 9 million people in the UK are always or often lonely.

You are right to want to cure your loneliness, of course. It is not just stifling and frightening and tedious; it is dangerous. According to researchers at Brigham Young University in Utah, US, (who reviewed data from studies that included 3.4 million people), loneliness can increase the risk of death by at least 30%. It is as dangerous as smoking 15 cigarettes a day, and more tightly linked to our mortality than better-known lifestyle risks like obesity and lack of exercise.

Loneliness ravages our immune system, leaves us more vulnerable to cancer, affects our heart health, lowers our pain threshold, raises our blood pressure, tightens our arteries and puts us at greater risk of dementia. It is, as I said, a real bastard.

And so, how do you stop being lonely?

The very first thing is to identify it. Naming the feeling, saying the words “I’m lonely” out loud, and preferably in the presence of a trusted human being, strips that malevolent emotion of some of its power. Loneliness relies on mystery to survive; it needs to nestle into your psyche undetected in order to make you feel your emptiest.

Loneliness is at its most potent when you mistake it for something else – for depression, for heartache, for garden variety sadness. When you find the courage to admit that you are lonely, you claim a little control back for yourself. Shame clings to loneliness like a pernicious little pilot fish, so it’s best to vanquish it as quickly as possible. It is not shameful to be lonely – it is human and it is natural and it is salvageable.

Next, you must truly understand it. Loneliness is not necessarily the same thing as social isolation. Perhaps the cruellest thing about loneliness is that it can exist in the company of others. You can feel lonely in a relationship, lonely at a party, lonely in the middle of a wedding with 200 guests. For my book on this very topic, The Friendship Cure, strangers generously shared their experiences of loneliness with me, and it was astonishing how often it affected healthy, sociable people with plenty of friends.

Perhaps my favourite description was from a woman called Amy, who said that loneliness is like being at a silent disco – a party where guests dance to music they’re listening to through headphones – but she’s the only person in the seething, sweaty crowd who can’t hear it. A man called Dave said he feels the sting of loneliness on his commute every day, somewhere in the space between work Dave and home Dave.

Between them, Amy and Dave have captured what loneliness is: it is the fear of being alone, more than the act of being alone. It is that frightening gap between our multiple identities, when we press pause on the persona we present to the world and actually have to confront who we may be as people. It is the chasm between our expectations of life and the reality. The feeling that there is something missing.

And so, in order to truly tame it, you must find out what is missing. Loneliness often thrives on a feeling of inadequacy, or self-doubt, or trauma. Group or individual therapy may help to work out what is bothering you. As a minimum, some earnest introspection is required. What could be the cause of your loneliness, especially if you are not physically alone or unable to leave the house? And if you are emotionally captive in your own home, what is stopping you from leaving? Cognitive behavioural therapy may help, or simply a game of netball at the local sports club.

Finally, you must push yourself to reconnect with people in order to bid it goodbye. When you are lonely, you are your most scared of social rejection, just when you need it the most. Studies by Professors John and Stephanie Cacioppo – a husband-wife team of loneliness researchers – suggest that loneliness makes us grouchier, more defensive, less open to socialising and more likely to push away the very people who could keep us company through an existential crisis (or at the very least get brunch). They also say it is as physically powerful as hunger or thirst.

And so, you must urgently find the courage to get out and interact with other human beings in a meaningful way. You must start by putting yourself literally in the presence of other human beings. That could begin with a message, a coffee date, a walk in the park, a Sunday roast at the pub. But – this is important – be strategic about your friendships and do an audit of the people in your life.

You could be lonely because you’re catching up with people who do not lift you up, nourish you, make your life lighter. The very best cure for loneliness is genuine, loyal, fierce, loving friendship – the kind that makes you feel complete, the kind that makes you feel sentimentally satiated. If you do not have these friends in your life already, you must seek them out. That is hard, but who ever said fighting loneliness was easy?

And then, you have one final task. Loneliness is a deeply private affliction, you see, but it’s also a modern public health crisis. To eradicate loneliness altogether we must launch an aggressive campaign of kindness towards other people. We must find a way to care and be cared for, to overhaul the way we interact as a species, to value friendship in a way we have forgotten. Only then, will we be able to stop the bastard.

• Kate Leaver is a freelance journalist who writes about women, pop culture and mental health. She is author of The Friendship Cure