For 20 years, Professor Ruut Veenhoven has been obsessed with our wellbeing. Now he's collected 8,000 pieces of research from more than 120 countries to create a World Database of Happiness he claims will ensure joie de vivre. Julia Stuart asks him to share the magic formula

On the sixth floor of the creepily silent social-sciences block at Erasmus University in Rotterdam is an office lined with box files. Two researchers sit silently tapping on computer keyboards. The only signs of personality are a potted rubber plant and a stuffed Garfield toy. Through the window are a row of tower blocks and a sky so obliterated by cloud that one could be forgiven for thinking the sun no longer existed.

Standing in the office is a bespectacled, bearded man in black trousers and black shirt. His grey jacket matches his grey hair and the grey carpet. Professor Ruut Veenhoven does not at first appear to be the most charismatic of individuals, but he is a man that many would be delighted to take into a quiet corner at a party. For the sociologist - and the contents of the 150-odd file boxes surrounding him - may well have something that each and every one of us is after: the secret of happiness.

For the past 20 years, Veenhoven, 62, the world's only Professor of Social Conditions for Human Happiness, has been collecting every scrap of reliable research from around the globe relating to life satisfaction. The result is the World Database of Happiness - more than 8,000 findings from 120 countries, which Veenhoven has sorted and made available on the internet for fellow researchers, students and those looking for ways to boost their joie de vivre.

Veenhoven nips out and returns with strong coffee. Clearly, his years of research have so far failed to reveal that nothing makes a woman happier than a chocolate biscuit on her saucer. The professor, who is also editor of the Journal of Happiness Studies, started the database in the early 1980s. Divided into two parts, the first rates the happiness of 90 nations on a scale of 0-10, based on 2,498 general population surveys from 1946 to 2004. The second contains 8,496 findings of the correlation between happiness and elements as diverse as looks, weight at birth, watching television and intelligence.

So what is the secret to happiness? The first step, says Veenhoven, is to live in the right place. Step forward Denmark, Switzerland and Malta, currently the happiest countries in the world, with scores of eight out of 10. Iceland and Ireland would also be very good choices, coming in at joint second with 7.8. You may also want to consider upping sticks to Ghana, a surprise entry at number three with 7.7. Canada, Guatemala, Luxembourg, the Netherlands and Sweden are having a gay old time at joint fourth with 7.6. Finland and Mexico follow gleefully at joint fifth, with 7.5.

"Happy countries are, typically, rich countries," explains Veenhoven. "They are, typically, countries with a lot of freedom, often well-governed and democratic, and they tend to be tolerant. Switzerland, for example, is one of the most democratic countries in the world, with a referendum system that varies from canton to canton."

How does he explain the presence of Ghana, Guatemala and Mexico in the top five, none of which is exactly known for its perfect democracy or high GDP? "Maybe the data for Ghana is somewhat inflated because sampling is not perfect there. But Latin American countries tend to be happier than you would expect them to be. We don't know why that is."

Interestingly, a high number of the happiest countries are, on the face of it, depressingly cold. "People are happier in moderate climates rather than in warm ones, even if you factor out wealth," explains Veenhoven. "One explanation is cultural. In the old days, colder climates required that people co-operated, especially men and women, otherwise you couldn't survive. That created the more equal culture that we enjoy now. In warmer countries, a woman can raise a crop by herself, for example, so men and women work less together. It's clear that people are happier if they live in equal, non-hierarchical conditions. The other explanation is biological. The pressure of illness is higher in tropical countries, whereas in colder climates people flourish and are happier."

And what about Britain? It sits, not entirely happily, at joint eighth with El Salvador and Honduras. Scoring 7.2, it is just behind Belgium with 7.3, and just ahead of Germany with 7.1. But if you think we're a miserable bunch, pity the glut of former Soviet-bloc countries, collecting around the bottom. And shed a tear for poor old Tanzania, which sits, head in hand, with the lowest score of 3.2, just below Zimbabwe.

OK, so what if you hightail it to Copenhagen, all your basic human needs are met - food, shelter, sex, friends - and you manage to find a challenging job to avoid the pit of despair that is boredom, but still you're miserable? According to Veenhoven, there is plenty that you can do about it. "One of the myths in psychology is that you are born either happy or not. It is true that some people have inherited depressive diseases, but these are the exceptions. Some people say that happiness is 60 per cent inherited. I think that these people are wrong. It could be as little as 20 per cent."

According to the social scientist's data, the biggest cause of unhappiness in the advanced world is what he calls "mild psychological limitations". A study that looked into the difference between the least and most happy Australians showed that 20 to 30 per cent was down to personality. "People can be a bit neurotic or socially clumsy, and I guess a lot of people would cheer up with a bit of therapy," he says. "Just improve yourself."

So, you've had therapy, your neuroticism is now well and truly coshed, but still you're not at happiness level eight. Maybe the answer is to get a better-paid job and indulge in some mood-boosting retail therapy? "If you want to be happier, getting more money isn't necessarily the solution," warns Veenhoven. "Education and income relates to about five per cent of someone's happiness."

But what would make a more significant impact would be to improve our intimate relationships - those with our friends, spouse and parents - as they constitute 10 to 15 per cent of happiness. Based on his data, Veenhoven would highly recommend marriage. "People are significantly happier when married than not, all over the world. I think it's a simple innate need."

And what of children - surely the next step to a life of contentment? Quick as a flash, Veenhoven, a father of three, prints out a graph from his computer. It shows the happiness levels of couples rising and peaking after marriage. Then, when children arrive, the black line plummets at such a rapid decent you can almost hear an aeroplane nosediving. "One of the surprises is that children don't add to happiness," says Veenhoven. "The presence of children detracts from the quality of marriage, at least to the quality of the modern, romantic, equal marriage. The situation becomes even more unhappy in modern marriages where the mother is working and looking after children."

But what of those who say that having children was the best thing they ever did? "These people might think so, but they don't know how life would have been if they hadn't had children." But the trend reverses at the age of 85, when those with children are happier than those without. "I do think that we have a need for companionship, so if you are childless but have a lot of friends, you easily compensate. But if you happen to reach 90, then most of your friends are dead and then it's an advantage to have children and grandchildren." What about faith? "Some would say go spiritual. I wouldn't. Some people equate happiness with spirituality, but I wouldn't say they are the same thing. I don't deny that, for some, spirituality is a source of satisfaction."

Rather happily, Veenhoven recommends drinking alcohol. "The optimum is two or three glasses a day. If you drink less you tend to be less happy; if you drink more you also tend to be less happy." Apparently, the type of alcohol doesn't matter. "The theory is that it's not so much the alcohol, it's the contact with others. But it does help people to relax. "As far as I can see, it's the same with going on holiday and to the theatre. People are happier if they go to the theatre than if they watch television. That doesn't mean that you should never watch television, but there should be variety and you should create opportunities to meet people."

Indeed, hobbies that get you moving tend to make you happier than those carried out slumped in an armchair. Gardeners, for example, are happier than TV watchers.

People should also consider doing voluntary work, since those who help others are also happier, but researchers are not quite sure about causality. "If you do nice things for others, that can make you happy, but it is true that happy people are nicer people, and also more active people," he says.

One would assume that good health was vital to a life of happiness. Indeed, if you become ill or suffer an injury, you become less happy, but the difference is less pronounced than one would expect. For example, people who become paralysed can recover their spirits to a remarkable degree, ending up about one point lower than average on the happiness scale.

According to the database's findings, the not-so-intelligent are just as happy as the brainy, and men and women are equally happy, on average. But there is a difference when it comes to age. Young women aged 15 to 30 tend to be happier than young men, probably because women tend to be more interested in older men, so those of their own age become frustrated. But after the age of 40 or 50, men tend to be happier. "One of the explanations is that men get more attractive as they get older and so are in a better position in the marriage market," says Veenhoven. "And most men die in the arms of their wife, while most wives die alone. The period of widowhood lasts seven to 10 years, and hurts and depresses the average person."

In general, is it not true that you get less happy as you age. But there is a fairly U-shaped dip for those in their thirties and forties. "The reason is that, at that time of life, people have less choice because they tend to have children, a mortgage and a demanding job, and if that way of life doesn't really suit them, it's less easy for them to escape," he says. Some aspects of happiness are completely out of our control. The Australian study found that about 10 per cent of the difference between the happy and the unhappy was down to sheer luck.

But is the effort required to become happier really worth it? Indeed it is, says Veenhoven. Happy people are healthier. A happy life predicates a long life, and the effect is about as strong as whether one does or doesn't smoke. Happy people are also better citizens, they vote more often, they are better informed, they give more to charity, they are better in intimate relationships, they are better lovers, better parents and better friends.

Is Veenhoven happy? "Some people expect me to be happy, but, of course, you can study it without being it. I'm like the average inhabitant of the Netherlands - that is, 7.6." I leave the professor feeling slightly happier, toying with the rather pleasant notion of a future life in a small town in Denmark (people who live in small towns are happier than those in cities) with my beloved, my pockets stuffed with condoms, a bottle of wine at hand, tending to my nasturtiums. The only thing missing would be a packet of chocolate biscuits.