People of all ages are at risk from diseases brought on by loneliness, new data has revealed. According to figures published by the Office for National Statistics, 2.4 million adult British residents – of all ages – suffer from chronic loneliness.

That number, combined with research highlighting the medical dangers posed by loneliness, could see the condition being recognised as the UK’s most dangerous health issue.

The latest figures form part of efforts to further the work of murdered MP Jo Cox, who launched a commission on loneliness shortly before her death in June 2016. They also follow the death in March of leading loneliness researcher John Cacioppo. Both Cacioppo and the Cox Commission, which was wound up last month, believed the number of adults suffering from loneliness in the UK is even higher than the ONS suggests – at up to 9 million adults.

Loneliness has long been linked with psychological problems like alcohol and drug abuse, eating disorders and depression. But Cacioppo’s key insight was that loneliness is fundamentally a biological problem. Its key causes are not in the mind or society, but in the body. And so is its most profound effect – death.

Analysis of 300,000 people in 148 studies found that loneliness is associated with a 50 per cent increase in mortality from any cause. This makes it comparable to smoking 15 cigarettes a day, and more dangerous than obesity.

As the lead researcher of the analysis, Julianne Holt-Lunstad, comments: “Loneliness significantly increases risk for premature mortality.”

Only when this shocking connection is understood will we start to treat loneliness as the public health emergency it is.

Loneliness has reached epidemic proportions in the UK, where researchers estimate that up to one in four people suffer from it. This number will certainly rise as the population ages, as more people live alone, and workplace automation further weakens bonds between people.

Cacioppo, who argued that the root cause of loneliness is evolution, pointed out that modern society is worlds away from the community-based life for which we are designed. Humans are such deeply social animals that it makes no more sense to consider a person in isolation than it does an ant or a bee. Even as adults, we are so dependent on our groups that for millennia, separation from them was a de facto death sentence.

For this reason, said Cacioppo, we evolved to experience social rejection in the same way as physical pain. Brain scans have shown that “social pain”, such as being shunned by a community, activates the same region – the dorsal anterior cingulate – as bodily trauma.

When we feel threatened by isolation, evolved responses drive us into a state of cognitive hypervigilance. We voraciously scour situations for social information that might allow us to reestablish personal connections.

Tragically, though, the very same hyper-alert state creates characteristic errors in social thinking that make us negatively misinterpret the information we detect. When we are lonely, we tend to misread others’ intentions as critical, competitive or threatening. We are less able to imagine things from their perspective.

A nation of isolation

At the same time, loneliness makes our own thinking more self-centred, caustic and distant. Responses made with this mindset can easily provoke the rejection we most fear, causing a self-fulfilling feedback loop. This, said Cacioppo, is the Catch 22 of loneliness: to escape it, we need other people, but the emotion itself impairs our ability to attract them.

In Cacioppo’s theory, cognitive bias causes us to poorly frame the problems of isolation. But the same insight suggests a route to tackling loneliness. Cognitive behavioural therapy (CBT) is a well established, proven intervention which is designed precisely to reframe faulty thinking about distressing situations.

Research conducted by Cacioppo and his colleagues compared CBT with enhancing social skills, giving greater social support and providing more chances for interaction. All reduced people’s loneliness, but social cognitive therapies were three times more effective than alternatives.

CBT is cost effective compared to other forms of therapy. But the numbers requiring help are daunting. They will become more so as structural and demographic forces weaken social connections further and result in ever more people living in isolation. Unless we find the will – and the money – to decisively tackle loneliness, the coming decades could see it recognised as Britain’s biggest killer.