Caffeine addiction may be genetic, according to a new meta-study.

Marilyn Cornelis, a research associate at the Harvard T.H. Chan School of Public Health, led the new study, examining previous investigations into use of the popular stimulant. She found eight genes in humans involved in the utilization of caffeine, two of which were previously identified. Two of the genes were involved with metabolism of the drug, while another pair carried the stimulant effect. Another two were involved in the metabolism of glucose (sugar) and lipids, which include fat-soluble proteins and waxes. The role these genes play in the absorption of caffeine is still unknown, although further research will study their actions.  

"Caffeine is the most widely consumed psychoactive substance in the world. Although demographic and social factors have been linked to habitual caffeine consumption, twin studies report a large heritable component," Cornelis wrote in a 2011 article.

Investigation of how genes can affect the consumption of caffeine products could assist researchers in learning why people have differing reactions to the products. One person may need three cups of coffee a day to feel energetic, while a drinker averaging one cup a day could feel jittery at those dosages.

Genes were found to control about 1.3 percent of caffeine consumption. Although this may sound like a small amount, it is roughly the same percentage as alcohol or tobacco.

The Coffee and Caffeine Genetics Consortium was established two years ago by researchers who were pursuing similar research on genes utilized in the uptake of caffeine. Together, the investigators were able to collect data sets and DNA samples from 120,000 people of European and African-American heritage.

Coffee contains many substances in addition to caffeine, actions of which could be controlled by other genes, in addition to the handful studied in these investigations. The stimulant itself may also be partly managed by other genes in the human body.

"The next question is who is benefiting most from coffee... 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 benefiting from non-caffeine components of coffee. So it's a little bit complex," Cornelis said.

Cornelis herself does not like the taste of coffee, but has taken to drinking the substance, in order to benefit from several recently-discovered health benefits.

Study of caffiene addiction and the role played be genetics in use of the drug was detailed in the journal Molecular Psychiatry.