Does happiness make for a healthy heart?

People who are usually happy and enthusiastic are less likely to develop heart disease than those who tend to be glum, scientists said on Thursday, and boosting positive emotions could help cut heart health risks.

U.S. researchers said their observational study was the first to show an independent relationship between positive emotions and coronary heart disease, but stressed that more work was needed before any treatment recommendations could be made.

"We desperately need rigorous clinical trials in this area. If the trials support our findings, then these results will be incredibly important in describing specifically what clinicians and/or patients could do to improve health," Karina Davidson of Columbia University Medical Center wrote in the study in the European Heart Journal.

Heart disease is the leading killer of men and women in Europe, the United States and most industrialized countries. Together with diabetes, cardiovascular diseases accounted for 32 percent of all deaths around the world in 2005, according to the World Health Organization.

Over 10 years, Davidson and her team followed 1,739 men and women who were taking part in a large health survey in Canada.

Trained nurses assessed the participants' heart disease risk and measured negative emotions like depression, hostility and anxiety, as well as positive emotions like joy, happiness, excitement, enthusiasm and contentment - collectively known as a "positive affect".

The researchers ranked the "positive affect" across five levels ranging from "none" to "extreme" and found that for each rank the risk of heart disease fell by 22 percent.

Davidson, who led the research, said her findings suggested it might be possible to help prevent heart disease by enhancing people's positive emotions.

"Participants with no positive affect were at a 22 percent higher risk of ... heart attack or angina ... than those with a little positive affect, who were themselves at 22 percent higher risk than those with moderate positive affect," she wrote.

"We also found that if someone who was usually positive had some depressive symptoms at the time of the survey, this did not affect their overall lower risk of heart disease."

Smoking, being overweight, a history of heart problems in the family and high blood pressure are traditionally seen as major risk factors for heart disease, but studies have also linked such things as intelligence and income levels to heart risks. Research published last week found intelligence is second only to smoking as a predictor of heart disease.

Ellen Mason of the British Heart Foundation (BHF) advocacy group said Thursday's study echoed previous findings which had prompted the BHF to delve deeper.

"The BHF is funding science to unravel the biology that underlies this link," she said.