Loneliness, like a bad cold, can spread among groups of people, new research finds.
While a runny nose might spread through handshakes, people likely catch the loneliness bug through negative interactions. A lonely person will be less trusting of others, essentially "making a mountain out of a molehill," said study researcher John Cacioppo, a psychologist at the University of Chicago. An odd look or phrasing by a friend that wouldn't even be noticed by a chipper person could be seen as an affront to the lonely, triggering a cycle of negative interactions that cause people to lose friends.
The upshot: A lonely person is likely to lose touch with another person, who in turn gets cut off from others, and both end up on the fringes of a social group.
"A lonely person who anticipates others are going to act negatively toward them finds evidence in their environment for that, partly because they anticipate it and partly because they elicit it," Cacioppo told LiveScience.
The finding, published in the December issue of the Journal of Personality and Social Psychology, suggests that loneliness is not a character trait, as in "that person is such a loner," but more of a state such as hunger, which evolved as a cue to motivate our ancestors to go find food.
"We're fundamentally a social species so we need others with whom we can cooperate and work," Cacioppo said. As such, loneliness may have been a cue to look out for anyone who might ostracize you, he added.
The results come from a study of more than 5,000 individuals who took part in the Framingham Heart Study between 1991 and 2001. Every two to four years, subjects completed questionnaires that measured depression and loneliness, gave their medical history and underwent a physical examination.
For instance, participants indicated how often during the previous week they had experienced a particular feeling, including loneliness, with four possible answers: 0–1 days, 1-2 days, 3-4 days and 5-7 days.
Participants also indicated friends and relatives, many of whom also took part in the study.
From this information, the researchers pieced together social networks showing connections between each individual and the average number of lonely days for the participant and that person's links.
They found loneliness is catchy with three degrees of separation. So a person's loneliness depended not just on his friend's loneliness but also on his friend's friend and his friend's friend's friend. Participants were 52 percent more likely to be lonely if a person to whom they were directly connected (one degree of separation) was lonely. For two degrees of separation, the number drops to 25 percent and 15 percent for three degrees.
The number of family members had no effect on loneliness scores.
Over time, lonely individuals become lonelier and transmit such feelings to others before severing ties. "People with few friends are more likely to become lonelier over time, which then makes it less likely that they will attract or try to form new social ties," they write. Such friendless individuals ended up on the outskirts of their social networks.
Loneliness has been linked with various mental and physical illnesses, including depression. And so the findings could have practical implications. "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," Cacioppo said.