People who need a cup of coffee - or three - to get through the day may be genetically predisposed to crave caffeine, according to a new study led by researchers at the Harvard School of Public Health.

Researchers have identified two genes associated with caffeine consumption, according to reports, both of which are involved in the breakdown of caffeine in the liver. People who have certain variations of those genes, known as CYP1A2 AND AHR, are able to metabolize the stimulant more efficiently than those who don't have it, which scientists say may increase their tolerance.

"It turns out that your liver, more than your brain, determines daily caffeine intake," said the study's senior author Dr. Neil Caporaso of the National Cancer Institute.

In a study of 47,000 adults across the U.S., researchers found that individuals with those genetic markers usually consumed about 40 more milligrams of caffeine than people with who did not have it, equal to one-third of a cup of coffee or an eight-ounce can of Coke.

Fortunately, jonesing for caffeine may have some health benefits. A recent study from the American Heart Association discovered that women who drank more than one cup of coffee - which is rich in antioxidants - per day had almost a 25 percent reduced chance of developing a stroke.