A person’s coffee-drinking behavior may be partially explained by genetics, according to research conducted by an international team of scientists led by Marilyn Cornelis, a research associate in the nutrition department at the Harvard School of Public Health.

The research indicates that eight genes in the human body may be related to coffee consumption, either directly or indirectly. While two genes had been previously identified in a study by Cornelis, six other genes have shed new light on how coffee works in the body.

Four of the eight genes are directly related to caffeine metabolism, or how fast one’s body gets rid of the caffeine; two others are related to neurotransmitters, which are connected to human behavior; and the last two are not related to caffeine directly but rather metabolic function, associated with glucose levels in the blood.

“[The two genes connected to neurotransmitters] could be related to why some people like [coffee],” said Daniel I. Chasman, a professor of medicine at Harvard Medical School and co-author of the research.

Yet it was the two glucose-related genes, according to Chasman, that were “most surprising.” Glucose levels are associated with the risk of diabetes, which could help explain some of coffee’s health benefits.

“It might be the connection between coffee drinking and protection from diabetes,” he said.

The research was a genome-wide association study, meaning that scientists chose a large population sample of participants who have a range of coffee-drinking behaviors. They then tested each genetic variant and tried to identify the variants associated with each phenotypic trait—for example, whether people enjoy coffee or not.

“The coffee data is by self-report,” Chasman said. “You sent [participants] the questionnaire and they told you how much coffee they drank. That’s how we measure it.” The study included responses from 120,000 people.

The eight genes accounted for 1.3 percent of the variance in coffee-drinking behaviors, which is similar to results obtained when looking at genetic determinants of smoking and alcohol consumption. Cornelis said the number was probably underestimated due to error in the self-report data. Other factors, including the availability of coffee and the cultural influence in each country, can also contribute to the differences in behaviors, according to the researchers.  

“For myself, I don’t drink coffee. I don’t like the taste of it.” Cornelis said. However, she said that she is trying to develop the habit because of the health benefits of caffeine.

According to Cornelis, this research specifically deals with coffee consumption behavior, which is distinct from her previous research that focused on caffeine consumption.

Cornelis said the research had important implications. “We showed the fact that our genes really do play a role in modulating our coffee intake in order to achieve our optimal stimulant effect of caffeine,” she said.

“The next question will be, are there other roles that these gene have? In most cases of the research, genes told us a little bit about outcome. But here we found out that perhaps the outcome could tell us a little bit about the genes,” she said.