Scientific research shows that happiness has real health implications, providing proof that happiness has a physiological effect on conditions such as diabetes and heart disease. Findings suggest that those who are happier heal more quickly, have stronger immune systems and, on average, live longer.
Happiness Protects the heart
A team from University College London found that happiness leads to lower levels of stress-inducing chemicals.  They found that when happier people experienced stress, they had low levels of a chemical that is associated with increasing the risk of heart disease.
It was found that those who were happy less often had higher levels of a bloodstream chemical called plasma fibrinogen, which shows if there is inflammation present in the body, an indicator of how great a risk a person has of developing heart disease in the future.
They also found that levels of cortisol - a stress hormone - were 32 per cent 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.
The lead author said:
"It has been suspected for the last few years that happier people may be healthier both mentally and physically than less happy people.
A 2009 study from the University of Pittsburgh involving nearly 100,000 women, found that those with an optimistic outlook had a 90 per cent lower risk of suffering heart disease and were 14 per cent less likely to die over the eight years the study took place than their pessimistic peers. 
Another 2009 study found a link between happiness and faster recovery from surface wounds.  Sixty participants who underwent a procedure that created a wound on the skin, and those with a positive attitude had a faster recovery time.
Happiness and colds
Research in 2003 found that people who are energetic, happy and relaxed are less likely to catch colds. 
The researchers found people who had a positive emotional attitude were not infected as often and experienced fewer symptoms than people with a negative emotional style.
After assessing 334 healthy volunteers, each volunteer got a squirt in the nose of a rhinovirus - the germ that causes colds.
The researchers kept the subjects under observation for five days to see whether or not they became infected and how they manifested symptoms.
Tests showed that positive people were no less likely to be infected with the virus. However, infection seemed to produce fewer signs and symptoms of illness.
"But a negative emotional style had no effect on whether or not people got sick."
He said that a more upbeat attitude may also help to reduce the risk of other infectious diseases, explaining:
"The symptoms of a cold are caused by the release of chemicals such as cytokines, histamines and bradykinins.
"The release of these chemicals is to some extent under the control of hormones that are produced when we experience various emotions.
Happiness and longevity
A study published by a Dutch professor last year found that after reviewing 30 studies carried out worldwide over periods ranging from one to 60 years, that the effects of happiness on longevity were "comparable to that of smoking or not", and said that happiness could lengthen life by between 7.5 and 10 years. 
He found that whilst feeling cheerful did not appear to prolong the lives of those already suffering from disease, on the contrary, among healthy populations, happiness appeared to protect against falling ill, thus prolonging life.
He found that happy people were more inclined to watch their weight, were more perceptive of symptoms of illness, and generally lived healthier lives.
The author explained: "Chronic unhappiness activates the fight-flight response, which is known to involve harmful effects in the long run such as higher blood pressure and a lower immune response."