Every moment of happiness counts when it comes to protecting your heart, researchers have said.
Happiness was more commonly linked to leisure, rather than work
A team from University College London said happiness leads to lower levels of stress-inducing chemicals.
They found that even when happier people experienced stress, they had low levels of a chemical which increases the risk of heart disease.
The research is published in Proceedings of the National Academy of Sciences.
It showed that those who were happy less often had higher levels of a bloodstream chemical called plasma fibrinogen, which shows if there is inflammation present.
It is an indicator of how great a risk a person has of developing heart disease in the future.
Researchers tested 116 men and 100 women who were taking part in a major study of thousands of London-based civil servants recruited between 1985 and 1988 when 35-55 years old to investigate the risk factors for coronary heart disease.
They carried out tests on people at work, during leisure periods and in the laboratory.
People were also asked whether or not they were happy at 33 moments during the day.
The researchers then evaluated how often people were happy in the course of the day.
Leisure was, unsurprisingly, linked with more happy moments than work.
It was found that some people reported they never felt happy, while others reported feeling occasional happiness and those who felt happy most of the time.
The results were adjusted for gender, age, employment status, weight, smoking habits and psychological distress.
Levels of cortisol - a stress hormone - were 32% lower in people who reported more happy moments.
Cortisol has been related to abdominal obesity, Type 2 diabetes, high blood pressure and autoimmune disorders.
The researchers also discovered happy people have had lower levels of fibrinogen when they were stressed.
Professor Jane Wardle, who worked on the study, said: "All the research to date has been on unhappiness, rather than happiness.
"This research suggests we should aim to maximise the happiness of the population."
Professor Andrew Steptoe, who led the study, said: "It has been suspected for the last few years that happier people may be healthier both mentally and physically than less happy people.
"What this study shows is that there are plausible biological pathways linking happiness with health."
He added: "What we find particularly interesting is that the associations between happiness and biological responses were independent of psychological distress.
"We already know that depression and anxiety are related to increased physical health risk. This study raises the intriguing possibility that the effect of happiness may be somewhat separate."
Professor Peter Weissberg, Medical Director at the British Heart Foundation said: "The results of this study build upon this team's work, which we are delighted to have supported.
"Evidence that emotional state is important for good heart health is growing and this shows that people who are happy and unstressed are likely to have less potentially dangerous stress chemicals in their bodies."