Just in time for the holidays comes a study that says loneliness spreads like a disease through people's social networks. In other words, that sad, isolated feeling is contagious.

It's a little hard to wrap your mind around the notion that social networks transport the urge to avoid social networks: "Surely a hermit who takes a newspaper is not a hermit in whom one can have complete confidence,'' as Tom Stoppard wrote in Arcadia. But this is because we think of loneliness as the absence of something. If you look at it instead as an active force, causing people to unplug the phone and not bother answering letters, then you can track it in a community.

The paper, in the latest Journal of Personality and Social Psychology, looked at data from the 61-year-old study of public health in Framingham, Massachusetts. Loneliness is important to epidemiologists because it correlates with lower immune function and higher risks of heart disease and diabetes. John T. Cacioppo, James H. Fowler, and Nicholas A. Christakis looked at the social networks of Framingham patients and concluded that "loneliness occurs in clusters, extends up to three degrees of separation, is disproportionately represented at the periphery of social networks, and spreads through a contagious process.'' When a lonely person drops out of a social network, the authors argue, he also cuts the connection that others have, through him, to that network.

A version of the paper, in pdf form, is here.

Happy holidays, everyone. Now get off the Internet and call a friend.