Working hard and relationships were the most important factors
Hard work may be the last thing people want as they return to their jobs after the festive break, but experts say it could be the key to happiness.
Researchers from Gothenburg University in Sweden have been studying published data on what makes people happy.
They believe working to achieve a goal, rather than attaining it, makes people more satisfied - although they said good relationships were important.
UK experts agreed, but said the work had to match an individual's strengths.
The Gothenburg team have been studying hundreds of interviews carried out with people across the world to find out what makes them feel fulfilled.
They said winning the lottery or achieving a goal at work gave a temporary high, but it did not last.
Instead, they found that working hard to reach a target was more fulfilling.
Lead researcher Dr Bengt Bruelde, from the university's philosophy department, said: "The important thing is to remain active.
"From our research the people who were most active got the most joy. It may sound tempting to relax on a beach, but if you do it for too long it stops being satisfying."
He said the full research would be published in the summer.
Averil Leimon, of the British Psychological Society, said: "Hard work is satisfying, but only if it suits you.
"The work has to use a person's strengths otherwise it can be demoralising.
"If it does, research has shown that the happiness is not even linked to the rewards that are on offer.
But she added: "Relationships can also have a significant impact. Strong relationships whether through family, the church, friends or work can inoculate you against feeling low."