“Our immune system evolved to hum along at peak capacity when we’re happy but to slow down dramatically when we’re not. This is why long-term unhappiness can literally kill you through its immune-suppressing effects, and why loneliness in late adulthood is deadlier than smoking. Indeed, once you’re over sixty-five, you’re better off smoking, drinking, or overeating with your friends than you are sitting at home alone.”
William von Hipple, from “The Social Leap”