Anyone who has ever been suddenly overcome with the urge to smile after passing a smiling person on the street is likely familiar with the idea that happiness is contagious. But having happy friends also tends to make you happier, according to a recent study published in the British Medical Journal. More surprisingly, the study also suggests that your overall happiness level can be influenced by the happiness of acquaintances and even by total strangers.

Your happiness level has huge implications for your health, including having a protective effect on your immune system and lowering the levels of stress hormones you produce. Being happy has also been associated with reduced pain perception, improved cardiac function, and reduced mortality.

In the study, American researchers examined data collected over 20 years from the Framingham Heart Study, an ongoing epidemiological study on heart health conducted in Framingham, Massachusetts, to determine how people’s ratings of their own happiness related to the happiness of other people in their social network. They found distinct happy and unhappy clusters significantly bigger than would be expected by chance.

Happy people tended to be at the center of social networks and had many friends who were also happy. Amazingly, happiness appears to spread outward not just to friends, but to friends of friends, and even to the friends of friends of friends, three degrees away from the original happy person. This means that the happiness of people you may not have ever met may influence your happiness level.

The researchers note that the effect is not just due to happy people connecting with other happy people, which they do. Beyond that, there seems to be a contagious process in which happiness spreads throughout the connections in a social network.

Interestingly, this spreading effect held true only for happiness. The researchers found that the spread of unhappiness was much less consistent and also more limited in scope.

The researchers estimate that each happy friend you have boosts your own chances of being happy by 9 percent. Having grumpy friends decreases it by about 7 percent. In general, the more friends you have, the more likely you are to be happy because each friend increases the probability that you're at the center of a network, which means you are more eligible to get a wave of happiness spreading through the social network.

While the data for the study was conducted prior to the advent of social networking Web sites on the internet, you can bet that such communities operate in a similar way. According to the researchers, since this type of technology enhances your contact with friends, it should support the kind of emotional contagion observed in the study.

The researchers also provide another reason to be cheerful during these tough economic times. According to the research, an extra chunk of money increases your odds of being happy only marginally — notably less than the odds of being happier if you have a happy friend. Maybe this year you can give the people in your social network a different type of holiday gift: a smile.

To join in a social network that allows you to connect with other people who share your health concerns, sign up for Healia Health Communities today. It just might make you happier :-)

_{Photo: Angi Unruh, Flickr, Creative Commons}