ON THE surface, Framingham, Massachusetts looks like any other American town. Unbeknown to most who pass through this serene place, however, it is a gold mine for medical research. Since 1948 three generations of residents in Framingham have participated in regular medical examinations originally intended to study the spread of heart disease. In the years since, researchers have also used Framingham to track obesity, smoking and even happiness over long periods of time. Now a new study that uses Framingham to analyse loneliness has found that it spreads very much like a communicable disease.

Feeling lonely is more than just unpleasant for those who yearn to be surrounded by warm relationships—it is a health hazard. Numerous studies show that loneliness reduces fruit-fly lifespans, increases the chances of mice developing diabetes, and causes a host of adverse effects in people, including cardiovascular disease, obesity and weakening of the immune system. Simply being surrounded by others is no cure. In people, the mere perception of being isolated is more than enough to create the bad health effects. However, in spite of its significant impact, precious little is known about how loneliness moves through communities.

Keen to shed some light on the mystery, John Cacioppo of the University of Chicago and his colleagues turned to the Framingham data. They found that all participants in the study were routinely asked to list people who would probably know their whereabouts in the next two to four years. Most importantly, they were asked to describe their relationship with each person as friend, spouse, sibling, neighbour or colleague. The original purpose of such questions was to help the researchers behind the heart-disease project stay in touch with participants even when they moved out of Framingham. But the loneliness team immediately recognised them as a way to identify social interactions.

Between 1983 and 2001, even more useful information was collected when participants were regularly asked to state how many days a week they felt certain feelings. One of the options they were presented with was “I felt lonely”. The answers, when combined with the data on where participants were living and who their friends and family were, allowed Dr Cacioppo and his colleagues to analyse the formation and transmission of isolation.

They report in the Journal of Personality and Social Psychology that loneliness formed in clusters of people, and that once one person in a social network started expressing feelings of loneliness, others within the same network would start to feel the same way. The effects spread as far as three degrees of separation. Those who had immediate contact with lonely people were around 50% more likely than average to feel lonely themselves. In people who knew people who had direct contact with lonely people, the figure was 25%. Those with three degrees of separation showed roughly a 10% increase.

The reason for the spread, the team argues, is because loneliness causes people to act towards others in a less generous and more negative fashion. As someone becomes lonely, he is more likely to interact with his friends negatively, and they are then more likely to interact with other friends negatively. If these interactions are repeated, the ties of friendships fray and people become lonelier and more isolated.

The effects were more noticeable among friends than family, and stronger among women than men. The researchers argue that this is because the costs of abandoning relationships are lower for friends than they are for family members, and because women look to friends for emotional and social support more than men do. When they fail to receive it, they are more likely to become lonely.

Yet these findings are only the first step. The team of researchers is starting to look at other towns and cities, to see if there are any public policies or city-planning techniques that thwart the spread of loneliness. No solutions have been discovered so far, but through the process of studying other communities the researchers have discovered that when it comes to having clusters of lonely people, Framingham, unfortunately, is very much like any other town in America.