Earlier this year, Denmark came top in a world map of happiness (the UK ranked 41st out of 178 nations). And for more than 30 years it has ranked first in European satisfaction surveys. So what makes Danes so content?

Researchers in this week's Christmas issue of the BMJ decided to find out why life satisfaction in Denmark substantially exceeds that in Sweden and Finland, the two countries most similar to Denmark.

Their hypotheses range from the unlikely (hair colour, genes, food and language) to the more plausible, such as family life, health and a prosperous economy.

However, their analysis points to two explanatory factors. Firstly, winning the 1992 European Football Championship put Danes in such a state of euphoria that the country has not been the same since. This may explain the high level of life satisfaction in Denmark after 1992, they write.

Secondly, while Danes are very satisfied, their expectations for the coming year are rather low. In contrast, Italy and Greece, which rank low on life satisfaction, rank high on expectations for the year to come, together with Swedes and Finns.

The causes of the stolid depth of Danish wellbeing are undoubtedly multifactorial, they say. The Danish football triumph of 1992 has had a lasting impact, but the satisfaction of the Danes began well before 1992, albeit at a more moderate level. The key factor that explains this, and that differentiates Danes from Swedes and Finns, seems to be that Danes have consistently low (and realistic) expectations for the year to come.

So the key to happiness may lie in the fact that if you lower your expectations enough you might feel a bit better next Christmas, they conclude.