Loneliness is deadlier than obesity and should be considered a major public health hazard, the biggest ever review into the problem has suggested.

Researchers in the US looked at 218 studies into the health effects of social isolation and loneliness involving nearly four million people.

They discovered that lonely people had a 50 per cent increased risk of early death, compared to those with good social connections. In contrast, obesity raises the chance of dying before the age of 70 by around 30 per cent.

Lead author Dr Julianne Holt-Lunstad, Professor of Psychology at Brigham Young University, Utah, said people should be preparing for retirement socially as well as financially, because for many people the workplace is their biggest source of companionship.

“Being connected to others socially is widely considered a fundamental human need—crucial to both well-being and survival,” she said.

“Extreme examples show infants in custodial care who lack human contact fail to thrive and often die, and indeed, social isolation or solitary confinement has been used as a form of punishment.

“Yet an increasing portion of the population now experiences isolation regularly.”