Are we wired to get wired? The folks at the Coffee and Caffeine Genetics Consortium believe so. They've found six new genetic variants associated with coffee consumption, in an analysis of about 120,000 java drinkers.
It's hardly surprising to discover that four of the highlighted genes are associated with metabolism of caffeine, the compound that helps wake us up and kick the brain into gear in the morning. But two of the genes linked to coffee consumption appear to be related to sugar and fats in the blood, which could lead to insights into some of coffee's reported beneficial health effects, according to the study published online Tuesday in the journal Molecular Psychiatry.
"We're really not sure how these play a role in caffeine behavior, if it's caffeine necessarily or some other component of coffee, or something we add to coffee," said study author Marilyn Cornelis, a nutrigeneticist at the Harvard School of Public Health.
More than half of Americans older than 18 drink coffee daily, gulping about 3.1 nine-ounce cups apiece, according to the Harvard School of Public Health.
Several studies have linked coffee drinking with positive health effects, including lower risk of Parkinson's disease, liver disease and type II diabetes. Effects on cancer development and cardiovascular issues are somewhat controversial, however.
Caffeine habits seem to be at least partially heritable, but the compound's effect varies widely among individuals, researchers have found.
"To identify factors that explain those differences is important because they might also impact differences in the health effects that coffee provides," Cornelis said.
The research drew on several genome databases of people of European and African American ancestry. It confirmed a previously discovered association between coffee habits and two genes, and uncovered similar correlations with six other genome areas.
Two of those areas could offer insight on taste conditioning and the habit-forming effects of coffee: They are involved in mood-related circuitry in the brain, the study found. One of the identified genes also has been associated with smoking initiation, a find that "possibly points to some addictive pathways," Cornelis said.
How humans came to have java genes is anyone's guess at this point. Several of the highlighted genes are related to drug metabolism in general, according to the study.
"Those are important not only to drugs that are mechanically produced, but to compounds we're exposed to in the environment," said Cornelis. "Maybe those have had important roles in protecting us over the years and have been maintained. Why, specifically for caffeine, it's not clear."
But once the genes adapted to the caffeine habit, though, they began driving human behavior, researchers suggest.