Why you decline another coffee

They exist in every office, the caffeine refuseniks. Smugly, they pass the coffee machine, pouring a sanctimonious glass of water as they explain that they had their one cup in the morning and that was enough.

Well, now their self-righteousness has at last been punctured by science: it’s not self-control that means people can restrict themselves to a single morning coffee, it’s genes.

Research has found that one gene in particular appears strongly linked to the amount of coffee people drink. Such is the effect that having a particular mutation, present in a large proportion of the population, means people take a cup a day less.

The scientists involved speculate that the reason why is not that they dislike coffee, but that those with this mutation are better at metabolising caffeine. Interestingly, there was no evidence the mutation made people enjoy coffee less.

‘‘The gene did not seem to affect preference for coffee, but it does affect consumption,’’ Nicola Pirastu, from Edinburgh University, said. There was a pleasing symmetry to this because previous work had identified genes that did affect how much people like the drink – but left consumption unchanged.

Pirastu said this was not as paradoxical as you might initially think.

‘‘When you think about it, how many times have you drunk bad coffee and thought, ‘This will do’ and kept on drinking?

‘‘If that happened with an apple you would just discard it. So there is a big disjunction between consumption and preference.’’

He thinks this is because we drink coffee not for taste but functionality – and that this gene mutation may make it more functional.

For his research, published in the journal Nature Scientific Reports, he looked at different communities in seven villages dotted across Italy, totalling 1300 people. Despite the populations being culturally very similar, a stark difference emerged in their espresso consumption. Those with a variation in this gene, called PDSS2, took more than a shot less.

The study could not examine why this is the case, but the same gene has previously been linked to the process of caffeine metabolising, and Pirastu said this was the most likely hint as to the mechanism.

To check if this was a universal effect, he and his colleagues also looked at 1700 Dutch coffee drinkers, where the favoured medium for caffeine is not espresso but filter coffee, drunk in considerably greater quantities. Here they found that those with the mutation again drunk around a cup less.

Pirastu said that the findings were not just about coffee. Showing how genes can drive consumption choices could be significant in combating poor diets.

‘‘The study shows there is a genetic component in our behaviours: we are wired to act in different ways. This will help us understand not only how we are behaving but why.

‘‘That is important if you want to change people’s habits, which is a big goal for public health."