Human beings are social animals and our biological, psychological, and social systems evolved to thrive in collaborative networks of people. In many societies, social networks are likely to thin as people age, leading in many cases to isolation and loneliness. In this article we review the evidence that social isolation affects health and mortality, whether or not the isolation is accompanied by subjective loneliness. Some studies suggest that the impact of isolation and loneliness on health and mortality are of the same order of magnitude as such risk factors as high blood pressure, obesity, and smoking.
