Dec. 5 (Bloomberg) -- Global recession got you down? Happy friends could do more to improve your mood than money, U.S. researchers said in the British Medical Journal.

Happiness is catching, rippling through social networks to up to three degrees of separation, researchers from Harvard Medical School and the University of California, San Diego, found after assessing more than 4,700 people over 20 years. The smaller the distance between friends, the bigger the effect, which lasted up to a year, the scientists said.

“This is probably the analogy that’s seen in financial markets where there’s a sudden stampede of emotional states,” said study co-author Nicholas Christakis, a professor in the department of health care policy at Harvard in Cambridge, Massachusetts. “It’s like if greed is infectious, so is happiness.”

A person is 25 percent more likely to be happy after a shift toward happiness in a friend who lives within 1 mile (1.6 kilometers), researchers found. Happy next-door neighbors made it 34 percent more probable that a person would feel good. Cheerful spouses, and siblings who live within a mile, boosted happiness to a smaller degree, while co-workers didn’t have an effect.

The findings came from the Framingham Heart Study, which has been running since 1948 in Framingham, Massachusetts. Researchers looked at questionnaires participants filled out from 1983 to 2003, using computer models to map 54,228 social ties listed by people in the study.

Happy, Hopeful

Researchers defined happiness as a perfect score on the questions “I felt hopeful about the future,” “I was happy,” “I enjoyed life” and “I felt that I was just as good as other people.”

The Framingham data had been used before to assess depression as a risk factor for heart disease, but this was the first time researchers looked at happiness across a broad network, Christakis said.

“We show that your happiness depends not only on your friends and family but on whether your friends of friends are happy,” he said in a telephone interview.

People’s good feelings may spread even to someone they don’t know. Researchers saw that happiness in people three degrees removed could make an individual 5.6 percent more likely to be happy. Having an extra $5,000 only made people 2 percent more likely to be happy, the authors said in a statement.

The study is “groundbreaking” because it shows that some psychological and social factors likely to influence health may spread across social networks, Andrew Steptoe, a professor at University College London, and Ana Diez Roux, a professor at the University of Michigan School of Public Health, wrote in an accompanying editorial.

Yale University researchers, however, said in a second study in the journal that social network research can be deceiving. Their research showed teenagers appeared more likely to have acne, headaches or be tall if those conditions were widespread among their friends, but that the results were insignificant once the data was adjusted for environmental factors.

To contact the reporter on this story: Naomi Kresge in Zurich at nkresge@bloomberg.net

Last Updated: December 4, 2008 19:01 EST