Caffeine fiends are off the hook. Their espresso dependency isn't entirely voluntary, they were just born that way. And those who get the jitters after half a cup of joe can't help it either. Coffee habits and caffeine tolerance are the product of our genes -- specifically eight genes.

That's the takeaway from the research recently conducted by the Coffee and Caffeine Genetics Consortium -- an international research team headed by Marilyn Cornelis, a scientist currently working at the Harvard T.H. Chan School of Public Health.

Most significantly, scientists isolated two new genes that dictate how caffeine is metabolized, while another two newly pinpointed genes were linked to coffee's psychoactive effects. These genes, researchers say, help explain why one cup is enough to give one person a solid boost, while another person may need three or four cups for the same effect.

The scientists involved in the study say the eight newly discovered coffee genes explain roughly 1.3 percent of our coffee-drinking behavior -- about the same amount of blame genes take for other habitual behaviors, like smoking and drinking.

Not that coffee should be considered bad for you the way health officials regard smoking and excessive alcohol consumption. In fact, Cornelis says there's some legitimacy to the science in recent years suggesting coffee drinking may have some health benefits.

More than half of all Americans over the age of 18 drink coffee daily; the average coffee drinker in the United States downs just more than three cups per day.

"I'm not a coffee drinker; I hate the taste of it," Cornelis said in a press release. "If there were more people like me in the study we wouldn't have found those genes."

But Cornelis says she's trying to develop a taste for the dark liquid. She and her colleagues think more research could uncover additional genes related to our coffee habits and to the beverage's effects on our bodies.

"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," she added. "So it's a little bit complex."

The research was published this week in the journal Molecular Psychiatry.