Recent research has revealed that mood of a person is strongly affected by the people around him. Research team led by Dr Nicholas Christakis, a sociologist at Harvard Medical School, and including Professor Fowler analyzed 53,228 social connections between 5,124 individuals over time.

Researchers said that how grumpy people feel can be influenced not only by the state of mind of those closest to us, but also by friends of friends that we have never met like ripples from "pebbles thrown into a pond".

Professor James Fowler of the University of California, said each 'unhappy connection' decreased the chance of a person being happy by seven per cent. However, the effect works both ways with each 'happy connection' increasing the chance of a person's happiness by nine per cent.

Data analysis showed that moods travel more freely in same-sex groups. Data also revealed that a happy friend increased the chances of someone being happy by 15 percent, a friend of a friend by about 10 per cent and a friend of a friend of a friend by about six per cent.

Researchers found that the mood of a cohabiting partner was less than 10 per cent likely to have an effect.

Researchers said that a whole range of phenomena are "transmitted" through networks of friends, including happiness and depression, obesity, drinking and smoking habits and even ill-health.