Why loneliness is hazardous to your health

In an increasing number of research studies, scientists have documented potentially unhealthy changes in the cardiovascular, immune, and nervous systems of chronically lonely people. This may help explain the observation that socially isolated people have shorter life spans and increased risk of a host of health problems, including heart disease and depression. The subjective experience of loneliness may be important here, not the actual number of social contacts a person has.
Miller G: Social Neuroscience: Why Loneliness Is Hazardous to Your Health. Science 331 (6014): 138-140 (2011).
http://www.sciencemag.org/content/331/6014/138.short