British scientists say they have discovered that a positive state of mind plays a key role in people's long term health.

Andrew Steptoe, professor at University College London, and his colleagues surveyed more than 200 middle-aged civil servants and found that the happiest people had lower levels of chemicals which are linked to heart disease and type II diabetes, according to the British journal Proceedings of the National Academies of Science.

The researchers monitored the emotional and physical state of the volunteers at work, at home and in a laboratory. They found the saliva of those who were happiest contained lower levels of cortisol, a stress hormone related to type II diabetes and high blood pressure.

Happier men had significantly lower heart rates - down from 76 beats a minute to 68-70. Men and women who were generally unhappy reacted to stress by producing in their blood more plasma fibrinogen chemicals - a strong predictor of cardiovascular disease.

Earlier in March, American researchers have found that a good bout of laughter every day prolongs a person's life as it stimulates the blood-flow and benefits the heart while depression poses the risk of an early death.

(Xinhua News Agency/Agencies April 20, 2005)