Coffee addicts may be born, not made. A recent international study led by Harvard researchers has identified six new genes linked to the way caffeine affects us.

The work, led by Marilyn Cornelis, a research associate at the Harvard T.H. Chan School of Public Health, found a total of eight genes, two of which had been identified in prior work by Cornelis and others. Two of the new genes were related to metabolism of caffeine and two were related to its psychoactive effects. The two remaining genes are related to lipid and glucose metabolism, but their role in coffee consumption isn't clear.

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The discoveries provide insight into why caffeine affects people differently, and how these effects influence coffee-drinking behavior, Cornelis said. One person, for example, may feel energized on a daily cup of coffee, while another might need four cups to feel the same effect. If the one-cup-a-day person drinks four cups, Cornelis said, he or she might feel jittery or have digestive problems. People have difference tolerance levels, in other words.

If you are a genetically slow caffeine metabolizer, it takes longer to clear caffeine from your body. Thus, less coffee will affect you more. 

See also: L.A.'s 10 Best New Coffee Shops of 2013

The findings suggest that people naturally modulate their coffee intake to experience the optimal effects exerted by caffeine and that the strongest genetic factors linked to increased coffee intake likely work by directly increasing caffeine metabolism.

“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,” said Cornelis, who herself “hates” coffee.

“The new candidate genes are not the ones we have focused on in the past, so this is an important step forward in coffee research,” she added.

The new genes explain about 1.3 percent of our coffee-drinking behavior. Though that may seem like a small amount, it is about the same as that reported for other habitual behaviors, such as smoking and alcohol consumption, Cornelis said.

Culture is probably a sizable influence too, the researchers said, but there’s also a strong chance that additional genes remain to be found, perhaps many more. The findings were published Tuesday in the journal Molecular Psychiatry, which happens to be our favorite coffee-break reading material.

The work was conducted by the international Coffee and Caffeine Genetics Consortium, which was launched two years ago by investigators who had published parallel work on caffeine-related genes. The researchers joined forces and recruited additional investigators, with each team contributing DNA samples and data sets, including surveys of the coffee-drinking habits of 120,000 people of European and African-American ancestry.

The genes found so far might represent only the tip of the iceberg on coffee consumption, Cornelis said. Not only may there be more genes involved in caffeine metabolism, coffee is rich in active compounds in addition to caffeine, some of which may also have physiological effects.

“The next question is who is benefiting most from coffee,” Cornelis said. “If, for example, caffeine is protective, individuals might have very similar physiological exposure to caffeine, once you balance the metabolism. But if coffee has other potentially protective constituents, those levels are going to be higher if you consume more cups, so they might actually be benefitting from non-caffeine components of coffee. So it’s a little bit complex.”


Now if scientists would only bring that same focus to breaking down the benefits of chocolate croissants!

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