Beta-endorphins (which alleviate depression) and HGH - human growth hormone (aids immunity and is important for growth, surprisingly) increased by 27% and 87% respectively when volunteers in a study group anticipated watching a humorous video.
Other research on laughter has found that it decreases stress hormones such as cortisol and epinephrine which suppress the immune system. It also increased NK (natural killer) cells which are known to attack tumour cells and cells infected with viruses. This means that laughter would be beneficial to those suffering from cancer and HIV.
Laughter also reduces high blood pressure and increases vascular blood flow while improving oxygenation of the blood. It relieves pain as well, possibly through the release of endorphins which are associated with feelings of well-being and relaxation.
Some research suggests that we are 30 times more likely to laugh in social settings than alone which supports the notion that laughter is more of a socially orientated behaviour. However, the exact figure of 30 times is a bit presumptuous and can't be taken as an exact calculation, but the general idea is supported by this study.
Laughter also relaxes muscles, a similar effect to anti-anxiety medications.
Increases salivary Immunoglobin A, an antibody that fights bacteria and infections. Interferon-gamma levels have been shown to increase due to laughter (these assist the immune system and are also beneficial in fighting tumours).
Apparently the body can't tell the difference between real and fake laughter suggesting that it is the muscular and respiratory effects that induce the feelings that go along with it, as opposed to the perception of what is or is not 'funny'. However, perception of humour is important for 'setting off' the laughter response most of the time. Laughter therapy can be an exception of this, in which participants are invited to laugh without cause, often to great benefit to their health.
Also, apparently, children laugh about 400 times per day and adults laugh around 15. Not sure how this was measured but the figures are so vastly different that its indicative at least that adults laugh less than children.
"Some physicians estimated that 80% of all illnesses are somehow stress related. Today, over 100 million Americans are suffering from some kind of stress-related problem. Stress is actually linked to the 6 leading causes of death in this country [America]; accidents, cirrhosis of the liver, suicide, coronary heart disease, cancer, and lung disease."
Exercises facial, leg, back, abdominal, respiratory and diaphragm muscles.
Contagious, hence the use of dubbed laughter in tv shows such as Friends.
Reduces dopac (major catabolite of dopamine and involved in production of epinephrine).
"Research now shows it is physiologically impossible to be in a state of appreciation and a state of fear at the same time. Thus, appreciation is the antidote to fear."
In a study of high-risk diabetic patients, those who were given medication and viewed comedy of their choice were compared to those who received medication. After 2 months those in the laughter group had lower epinephrine and norepinephrine levels (adrenaline and noradrenaline respectively) which implied that they felt less stress. They also had lower levels of inflammation and higher levels of HDL (commonly referred to as being 'good cholesterol'). After a year the laughter group had an increase of HDL by 26% compared to 3% in the medication only group. The laughter group also had a 66% decrease in harmful C-reactive proteins compared to 26% in the other group.
If laughter leads to hiccuping and coughing it can help clear the respiratory tract of mucus plugs.
"Hospitalized children who see clown shows have shorter hospital stays than those who don't."
I have no idea where I got those quotations from :P, ack well...