Happiness is catching, new research has confirmed, and depends on how cheerful about life your friends feel.

Happiness is spread through social networks and exists in clusters of close friends and neighbours, according to a study published today in the British Medical Journal. Being around happy people at work does not help, the research found... - happiness is most contagious in your street. Living next door to somebody who becomes happy can increase your own chances of happiness by 34%.

The research was carried out by academics from the University of California in San Diego, who used data from the Framingham heart study in Massachussetts, which has been going since 1948. Most of the children and many of the grandchildren of the original participants are regularly monitored to establish the state of their health.

Professors Nicholas Christakis and James Fowler have carried out research on the impact of social networks on other aspects of health and found that they influence obesity and smoking habits. The current study was designed to find out whether happiness is peculiar to an individual or dependent on the people around him or her.

The researchers assessed the happiness of people (whom they termed egos) and their friends, neighbours and relations (alters). They asked whether they agreed or disagreed with four statements relating to the previous week: "I felt hopeful about the future," "I was happy," "I enjoyed life," "I felt that I was just as good as other people." Happiness was a perfect score in all four. The academics found it does not matter how many friends you have.

"Having additional social contacts is helpful to the ego's happiness only if the extra social contacts are happy themselves," said Chistakis and Fowler. What is important is how happy your friends are and how close to you they live.