US researchers have identified two genes that could explain why some of us are tempted to reach for those caffeine-packed drinks.
Dr Marilyn Cornelis of the Harvard School of Public Health and Dr Neil Caporaso of the National Cancer Institute in the USA carried out a genome-wide association study of over 47,000 adults from five US studies. Their findings identified two genes called CYP1A2 and AHR associated with high consumption of caffeinated products such as tea, coffee and chocolate.
Previous twin studies have shown that genetics could play a role in our caffeine preferences, but it was unclear which genes were involved. Dr Caporaso said people with some variants of these genes consume more caffeine, on average about 40mg, which is the equivalent of a third of a cup of coffee.
CYP1A2 is expressed in the liver and 'is up to 95 percent responsible for caffeine metabolism', Dr Cornelis said. The team also linked to caffeine consumption a region of DNA near a gene called AHR, which regulates how CYP1A2 is expressed.
'When trying to tease out the genetics of behaviours such as overeating or alcoholism, researchers commonly ask whether the genes at play are ones that regulate how a substance is metabolised or ones that mediate the body's response. With caffeine, there is now a clear answer: It's in the liver, not in your brain', said Dr Caporaso.
The study was published in the journal PLoS Genetics.