April 7, 2011 -- DNA may play a large role in determining how much caffeine people consume in beverages such as coffee, tea, and soda and food such as chocolate, new research indicates.
Scientists from the Harvard School of Public Health, the National Cancer Institute, and other institutions say they have discovered two genetic variations that influence the metabolism of caffeine and are associated with how much caffeine people consume. People with particular variations of two specific genes are more likely to consume caffeine, and to drink more of it when they do, study leader Marilyn C. Cornelis, PhD, of the Harvard School of Public Health, tells WebMD.

Genes and Coffee

The genes are identified as CYP1A2, long known to play some role in caffeine metabolism, and another called AHR, which affects regulation of CYP1A2.
All people have both genes, but the study, involving more than 47,000 middle-aged Americans of European descent, finds that people with the highest-consumption variant for either gene consumed about 40 milligrams more caffeine than people with the lowest-consumption gene varieties. Forty milligrams is the equivalent of 1/3 cup of caffeinated coffee or one can of soda.
Cornelis says her own father may carry the variations that correspond to higher caffeine consumption because he drinks “at least 10 cups” daily.
“He’s not trying to achieve pleasurable effects,” she tells WebMD. “Rather, he’s trying to maintain levels as a means to avoid the withdrawal symptoms. Without a cup he’d wake up in the middle of the night with a headache.”
That suggests he “could possibly have the genetic profile of a fast caffeine metabolizer,” she says in an email.
The researchers say it’s likely that genetics plays a major role in other behaviors, such as alcohol consumption and smoking.

Coffee Consumption

The researchers say in a news release that their conclusions are based on an analysis of five studies conducted between 1984 and 2001. Average caffeine consumption via coffee, tea, caffeinated sodas, or chocolate was recorded.
About 80% of the caffeine intake among participants involved in the analysis was from coffee, similar to the adult caffeine consumption in the U.S. “We propose that those with the genotype corresponding to ‘higher caffeine consumption’ are metabolizing caffeine at a different rate vs. those with the ‘lower caffeine consumption’ genotype, and so require a different level of intake to maintain or achieve physiological caffeine levels that produce pleasurable effects,” Cornelis tells WebMD.
So what does this mean?
“Clearly these genetic variants are affecting how our body processes caffeine,” she tells WebMD.
Caffeine is implicated in a number of medical and physiological conditions. Caffeine affects mood, sleep patterns, energy levels, and mental and physical performance.
“Caffeinated products, particularly coffee, have long been implicated in various health conditions.”
She says that “studying the effects of caffeine, say, on the cardiovascular system, would be challenging if the group of subjects we’re studying process caffeine differently.”

More ‘Caffeine Genes’ May Be Identified

This genetic knowledge could be used “to advance caffeine research and potentially identify subgroups, defined by genotype, of the population most susceptible to the effects of caffeine,” Cornelis tells WebMD. “More research on the precise function of these variants is needed, however, and there are likely more ‘caffeine genes’ to be identified.”
She tells WebMD that her team’s findings “demonstrate that our search approach -- scanning the entire human genome -- works.”
Also, it shows for the first time that genetics may be responsible for inherited differences in how people drink coffee.
The study is published in the April issue of PLoS Genetics.