The amount of caffeine we drink may not be grounded in habit or lack of sleep. New research suggests that our own DNA is the biggest factor in determining whether we reach for that cup of java each morning.
A new study published in PLoS Genetics found that people who carry a particular version of two specific genes were much more likely to consume caffeine. The genes identified were CYP1A2, previously linked to the metabolism of caffeine, and AHR, involved in the regulation of CYP1A2.
"We know caffeine had an inherited component but for the first time we know specifically the major genes involved," said Dr. Neil Caporaso, branch chief of genetic epidemiology at the National Cancer Institute and senior investigator for the study. "Genetic studies have identified many associations with diseases, but very few for diet agents."
"We have a very clear finding for two genes that are highly plausible," he continued. "This offers a scalpel to investigate the many health effects of caffeine."
Harvard researchers analyzed the genes of more than 47,000 middle-aged Americans. Those in the study who had the "high-consumption" version of the gene drank about 40 mg more caffeine per day than people who had the "low-consumption" variant. Authors noted that this amount equals about an extra can of soda or a third of a cup of coffee.
The study noted that nine out of 10 adults eat or drink caffeine regularly and eight in 10 Americans who consume caffeine are coffee drinkers.
Caporaso said that it was "astonishing" to find the two associated caffeine genes after searching more than 300,000 genetic markers. And, since one gene regulates the other, "to find them both holding hands was amazing," he said.
"Caffeine is the most commonly consumed substance with important psychoactive properties," said Caporaso. "Just try skipping your coffee for two days! Knowing the specifics of the genetic influence on its disposition will jumpstart lots of studies."
Researchers said that the information will act as a new tool to study physical effects influenced by caffeine, including exercise, sleep, anxiety and many other medical conditions. They also hope to study why people react differently to caffeine and how the drug can impact other conditions like diabetes and heart disease.
"This is one of the most obvious examples of where we're going with personalized medicine," said Dr. Michael Watson, executive director of the American College of Medical Genetics. "We're able to look at the variations and the way people deal with drugs and the way they metabolize them."
"This is not something that just geneticists are going to be doing in the future," said Watson. "Once we figure it out, a person's primary care physician will use the information with their patients."