A newly-published study has shown that loneliness can spread from one person to another, like a disease.

Researchers used information from the Framingham Heart Study, which began in nineteen forty-eight. The Framingham study gathers information about physical and mental health, personal behavior and diet. At first, the study involved about five thousand people in the American state of Massachusetts. Now, more than twelve thousand individuals are taking part.

Information from the Framingham study showed earlier that happiness can spread from person to person. So can behaviors like obesity and the ability to stop smoking.

University of Chicago psychologist John Cacioppo led the recent study. He and other researchers attempted to show how often people felt lonely. They found that the feeling of loneliness spread through social groups.

Having a social connection with a lonely person increased the chances that another individual would feel lonely. In fact, a friend of a lonely person was fifty-two percent more likely to develop feelings of loneliness. A friend of that person was twenty-five percent more likely. The researchers say this shows that a person could indirectly be affected by someone's loneliness.

The effect was strongest among friends. Neighbors were the second most affected group. The effect was weaker on husbands and wives, and brothers and sisters. The researchers also found that loneliness spread more easily among women than men.

The new study involved researchers from the University of Chicago, Harvard University and the University of California at San Diego.

A report on the findings was published this month in The Journal of Personality and Social Psychology.

The New York Times newspaper reports that, on average, people experience feelings of loneliness about forty-eight days a year. Yet the study found that having a friend who is lonely can add about seventeen days a year of loneliness. It also found that every additional friend can decrease loneliness by about five percent, or two and a half fewer lonely days.

Loneliness has been linked to health problems like depression and sleeping difficulties. The researchers believe that knowing the causes of loneliness could help in reducing it.

The researchers did not study how loneliness spreads. However, Professor Cacioppo says existing research offers some possibilities. Lonely people are often mistrustful of others. This behavior spreads from one person to another, along with the emotion responsible for it.

The study suggests that people can take steps to stop the spread of loneliness. They can do this by helping individuals they know who may be experiencing loneliness. The result can be helpful to the whole social group.