GENETICS may be what separates people who can't function without coffee and those who never touch the stuff, according to a new large-scale study.
Scientists have long known that your DNA influences how much java you consume, but the new study has pinpointed six new genetic variants associated with habitual coffee drinking.
Four of the new variants implicate genes that are involved with caffeine, either in how the body breaks it down or in its stimulating effects, the researchers said in the paper.
The two other newly implicated genes were the most surprising, as they are not clearly linked to coffee of caffeine, but rather involved with cholesterol levels and blood sugar.
Researchers believe these findings could help to explain why a given amount of coffee or caffeine has different effects on different people, and provides a genetic basis for future research exploring the links between coffee and health.
To make their findings published in the journal 'Molecular Psychiatry', researchers from Harvard School of Public Health and Brigham and Women's Hospital analysed 20,000 regular coffee drinks of European and African American ancestry.
Researchers also analysed the results of around two dozen previous studies with a combined total of more than 120,000 people. Each participant described how much coffee they consumed a day and also allowed scientists to scan their DNA.
The new work looked for minute differences in the DNA of participants that were associated with drinking more or less coffee.
The resultant study suggests that people naturally curb their coffee intake to achieve the best effect caffeine can give them, and that the strongest genetic factors linked to increased coffee intake likely work by directly increasing caffeine metabolism.
Marilyn Cornelis, research associate in the Department of Nutrition at Harvard School of Public Health and lead author of the study, said: "Coffee and caffeine have been linked to beneficial and adverse health effects. Our findings may allow us to identify subgroups of people most likely to benefit from increasing or decreasing coffee consumption for optimal health."
Daniel Chasman, associate professor at Brigham and Women's Hospital and the study's senior author, said: "Like previous genetic analyses of smoking and alcohol consumption, this research serves as an example of how genetics can influence some types of habitual behaviour."
Ms Cornelis went on to explain that none of the identified genetic variants was related to how intensely a person tastes coffee, and Cornelis said that surprised her.
She added that doesn't drink coffee, because she can't stand the stuff.