Jeremy Laurance: It turns out that everybody needs good neighbours

Anyone who has ever tried to buy a house knows the presence of a good school nearby can boost prices by many thousands of pounds. But would you pay a similar premium to live next door to a cheerful neighbour?

It has always amazed me that estate agents never include (non-libellous) details of the neighbours, who have a far greater impact on your life than the bus service, size of a box room or the distance to the nearest Tesco. Why not pictures of them too, preferably grinning from ear to ear?

The idea is not as daft as it seems. Doctors have discovered that our own happiness is dependent on the moods of those around us. If you are surrounded by happy people, you are more likely to feel happy yourself. And, unexpectedly, happy neighbours matter more than happy friends, siblings or even spouses.

It is well known that people can "catch" each other's moods by "emotional contagion". Students assigned to share with a depressed room mate become depressed themselves, while waiters who provide "service with a smile" see the benefits in the size of their tips.

Yet we still think happiness depends on individual experience. Lottery wins and job success are obvious sources of happiness, just as divorce, bereavement and redundancy are linked with unhappiness. What has not been appreciated is how a key determinant of human happiness is the happiness of others.

Now a study of almost 5,000 people whose happiness was monitored over 20 years from 1983 to 2003 has found that happiness is like a virus – it is catching and close physical proximity is a key factor in its spread.

The biggest boost to happiness came from living next door to a happy neighbour, increasing the chances of happiness by 34 per cent. This was much greater than the effect of other neighbours living in the same apartment block, demonstrating the importance of physical proximity. Frequent social contact matters more to the spread of happiness than deep social connections, it seems. Spouses have a smaller effect – you have an 8 per cent higher likelihood of being happy if your partner is. Happiness spreads much more readily through same-sex relationships than opposite sex ones.

There was, however, one exception to the rule about proximity. The spread of happiness did not extend to co-workers. Perhaps employees see themselves as rivals for attention, resources and pay – and there may even be a secret relief in others' misfortune.

Shared happiness unites communities and encourages social cohesion, say the researchers from Harvard Medical School in the British Medical Journal. So go on, smile!

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Michael Rosen, children's laureate, has written a poem to mark the NHS's 60th anniversary called "These are the hands". "The NHS brought my five children into the world and saved the lives of two of them," he said. What he didn't mention was that the NHS was unable to prevent the death of his 18-year-old son, from meningitis. That he can still celebrate it is testimony to the generosity of his great heart.