Loneliness is as deadly as smoking 15 cigarettes a day

A 2015 meta-analysis of 148 studies by Julianne Holt-Lunstad found that social isolation increases mortality risk by 29% — comparable to smoking 15 cigarettes a day and more dangerous than obesity. The mechanism involves elevated cortisol, poor sleep, inflammation, and reduced immune function, all triggered by the chronic stress of feeling disconnected. The UK, US, and Japan have appointed ministers for loneliness in response to what researchers now call an epidemic.

Source: Holt-Lunstad, J., Smith, T.B. & Layton, J.B., 'Social Relationships and Mortality Risk', PLOS Medicine (2010)