Loneliness, like a bad cold, can spread among groups of people, research at the University of Chicago, the University of California-San Diego and Harvard shows.

Using longitudinal data from a large-scale study that has been following health conditions for more than 60 years, a team of scholars found that lonely people tend to share their loneliness with others. Gradually over time, a group of lonely, disconnected people moves to the fringes of social networks.

"We detected an extraordinary pattern of contagion that leads people to be moved to the edge of the social network when they become lonely," said University of Chicago psychologist John Cacioppo, one member of the study team and one of the nation's leading scholars of loneliness. "On the periphery people have fewer friends, yet their loneliness leads them to losing the few ties they have left."

Other members of the study team were James Fowler, Associate Professor of Political Science at the University of California-San Diego, and Nicholas Christakis, Professor of Medicine and Professor of Medical Sociology in the Harvard Medical School.

Before relationships are severed, people on the periphery transmit feelings of loneliness to their remaining friends, who also become lonely. "These reinforcing effects mean that our social fabric can fray at the edges, like a yarn that comes loose at the end of a crocheted sweater," said Cacioppo, the Tiffany & Margaret Blake Distinguished Service Professor in Psychology.

Because loneliness is associated with a variety of mental and physical diseases that can shorten life, Cacioppo said it is important for people to recognize loneliness and help those people connect with their social group before the lonely individuals move to the edges.

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The scholars' findings were published in the article, "Alone in the Crowd: The Structure and Spread of Loneliness in a Large Social Network," published in the December issue of the Journal of Personality and Social Psychology.

For the study, the team examined records of the Framingham Heart Study, which has studied people in Framingham, Mass. since 1948. The original group, including more than 5,209 people, was originally studied for the risks of cardiovascular disease.

The study has since been expanded to include about 12,000 people, as the children and the grandchildren of the original group and others have been included to diversify the population sample. The Framingham study now includes more tests, including measures of loneliness and depression. The second generation in the study, which includes 5,124 people, was the focus of the loneliness research.

Because the study is longitudinal, researchers kept in touch with the subjects every two to four years and accordingly collected names of friends who knew the subjects. Those records became an excellent source of information about the people's social networks.

By constructing graphs that charted the subjects' friendship histories and information about their reports of loneliness, researchers were able to establish a pattern of loneliness that spread as people reported fewer close friends. The data showed that lonely people "infected" the people around them with loneliness, and those people moved to the edges of social circles.

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The team found that the next-door neighbors in the survey who experienced an increase of one day of loneliness a week prompted an increase in loneliness among their neighbors who were their close friends. The loneliness spread as the neighbors spent less time together.

Previous work suggested that women rely on emotional support more than men do, and in this study women were more likely than men to report "catching" loneliness from others. People's chances of becoming lonely were more likely to be caused by changes in friendship networks than changes in family networks.

Research also shows that as people become lonely, they become less trustful of others, and a cycle develops that makes it harder for them to form friendships. Societies seem to develop a natural tendency to shed these lonely people, something that is mirrored in tests of monkeys, who tend to drive off members of their groups who have been removed from a colony and then reintroduced, Cacioppo said.

That pattern makes it all the more important to recognize loneliness and deal with it before it spreads, he said.

"Society may benefit by aggressively targeting the people in the periphery to help repair their social networks and to create a protective barrier against loneliness that can keep the whole network from unraveling," he said.

The research was supported by a grant from the National Institute on Aging.

"Previous research has shown that loneliness and lack of social connection can have a significant negative effect on the overall health and well-being of older people," said Richard Suzman, Ph.D., director of the NIA's Division of Behavioral and Social Research, which funded the research. "This pioneering research into the connections of individuals within their social networks has important implications for the larger issue of social interactions and health."