Loneliness has been linked to depression and other health problems. Now, a study says it c

an also spread. A friend of a lonely person was 52% more likely to develop feelings of loneliness. And a friend of that friend was 25% more likely to do the same. Earlier findings showed that happiness, fatness and the ability to stop smoking can also grow like infections within social groups. The findings all come from a major health study in the American town of Framingham, Massachusetts.

The study began in 1948 to investigate the causes of heart disease. Since then, more tests have been added, including measures of loneliness and depression.

The new findings involved more than 5,000 people in the second generation of the Framingham Heart Study. The researchers examined friendship histories and reports of loneliness. The results established a pattern that spread as people reported fewer close friends.

For example, loneliness can affect relationships between next-door neighbors. The loneliness spreads as neighbors who were close friends now spend less time together. The study also found that loneliness spreads more easily among women than men.

Researchers from the University of Chicago, Harvard and the University of California, San Diego, did the study. The findings appeared last month in the Journal of Personality and Social Psychology.

The average person is said to experience feelings of loneliness about 48 days a year. The study found that having a lonely friend can add about 17 days. But every additional friend can decrease loneliness by about 5%, or two and a half days.

Lonely people become less and less trusting of others. This makes it more and more difficult for them to make friends—and more likely that society will reject them.

John Cacioppo at the University of Chicago led the study. He says it is important to recognize and deal with loneliness. He says people who have been pushed to the edges of society should receive help to repair their social networks.

The aim should be to aggressively create what he calls a "protective barrier" against loneliness. This barrier, he says, can keep the whole network from coming apart.

Besides loneliness, which of the following can also spread among people？

A．Friendship.

B．Happiness.

C．Depression.

D．Smoking.