Young adults are more likely to feel lonely than older generations, according to a study by the Office for National Statistics.
The research found that almost 10 per cent of 16 to 24-year-olds said they "always or often" felt lonely - the highest proportion of any group.
The figure was more than three times higher than among over 65s, with researchers suggesting people could become more "resilient" to loneliness with age.
Earlier this year Theresa May set out plans to tackle the issue as she warned that millions of people were suffering from a lack of regular contact with others.
The ONS study, based on a survey of more than 10,000 adults, found that people over 75 were 63 times less likely to report feeling lonely than those under 24.
Experts said loneliness is linked to a lack of permanence or sense of belonging - such as young renters who felt few connections to their local community.
Cal Strode, of the Mental Health Foundation, said that loneliness among young people could be driven by social media and the "digital world".
"Teens can have thousands of friends online and yet feel unsupported and isolated. Technology, including social media, could be exacerbating social isolation," he said.
Most at-risk groups
The study found women were consistently more likely to report issues with loneliness than men, though this could be due to under-reporting by men.
Older women who had been widowed and were living alone were particularly likely to be lonely, especially if they also suffered from illness.
People who were single, middle-aged, living alone and with poor health, were identified as another peak of loneliness.
Those least likely to be affected were middle-aged, homeowners who were in relationships and involved in their local community.
As harmful as smoking
Izzi Seccombe, chair of the Local Government Association's committee on well-being, said: "The harm loneliness can cause, both physically and mentally, can be devastating to people of all ages - it is a serious public health concern which studies suggest can be as harmful as smoking 15 cigarettes a day.
"We all need to be on the lookout for each other, which could be as simple as a quick visit to check on a neighbour, who could be a young mum without any family nearby, or an older person living alone," said Ms Seccombe, who is leader of Warwickshire County Council.
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