According to psychologist Professor Ed Diener there is no one key to happiness but a set of ingredients that are vital. First, family and friends are crucial - the wider and deeper the relationships with those around you the better. It is even suggested that friendship can ward off germs. Our brains control many of the mechanisms in our bodies which are responsible for disease. Just as stress can trigger ill health, it is thought that friendship and happiness can have a protective effect. Marriage also seems to be very important. According to research the effect of marriage adds an average seven years to the life of a man and something like four for a woman.
The second vital ingredient is having meaning in life, a belief in something bigger than yourself - from religion, spirituality or a philosophy of life. The third element is having goals embedded in your long term values that you're working for, but also that you find enjoyable.Psychologists argue that we need to find fulfilment through having goals that are interesting to work on and which use our strengths and abilities.

(BBC News "The Science of Happiness" By Mike Rudin)