Tortured artists and sappy songwriters have long sensed that loneliness is not such a good thing, but now we know for a fact that it is detrimental to your mental and physical well-being. A growing body of research shows that feelings of emotional isolation can literally both make people ill and hasten death. Contrary to what was once believed, scientists are now ranking loneliness “as high a risk factor for mortality as smoking.”

“Psychobiologists can now show that loneliness sends misleading hormonal signals, rejiggers the molecules on genes that govern behavior, and wrenches a slew of other systems out of whack,” New Republic reports. “A partial list of the physical diseases thought to be caused or exacerbated by loneliness would include Alzheimer’s, obesity, diabetes, high blood pressure, heart disease, neurodegenerative diseases, and even cancer—tumors can metastasize faster in lonely people.”

The proof is everywhere: From baby macaques raised in isolation who become sick and underdeveloped, to studies from the 80’s showing how HIV-infected gay men were significantly more likely to die if they were closeted (i.e. feeling isolated) than if they were “out” and felt included in a group. While Loneliness Studies is only a recently growing field, it has already revealed so much about the scientific legitimacy of the mind-body connection associated with loneliness.

The theory explains that we are evolutionarily hardwired to live as part of a group — back in the Savannah days, humans that strayed away from the tribe would likely be devoured by wild animals, so more socially-inclined humans were naturally selected. This is why our body releases health-threatening stress hormones, like cortisol, when we feel isolated: to warn us that our isolation is a threat to our survival.

Of course, loneliness “is not synonymous with being alone, nor does being with others guarantee protection from feelings of loneliness,” writes John Cacioppo, a leading psychologist in the field. The key is the feeling of rejection, or lack of intimacy. But hopefully now that emotional isolation is being taken seriously as a public health issue, we can finally implement the social change needed to stop stigmatizing and rejecting those we might view as outsiders. And no, following Amanda Bynes on Twitter doesn’t count.