The desire to keep drinking coffee may not be so much a question of lifestyle or not getting enough sleep, but rather a consequence of having a particular set of genes, US researchers reported in the journal PLoS Genetics. The authors explained that people who have two versions of two particular genes have a much higher chance of wanting to consume more caffeine than others.

The authors explained that previous studies on twins appear to show that how much coffee an individual drinks is partly hereditary. However, nobody could pinpoint which genes drove this caffeine preference.

These genes are CYP1A2 and AHR. CYP1A2 is thought to be involved in caffeine metabolism, while AHR has a role in CYP1A2 regulation. Both genes are involved in the breakdown of caffeine in the liver.

Senior researcher, Dr. Neil Caporaso, of the National Cancer Institute, said:

“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. This offers a scalpel to investigate the many health effects of caffeine.”

It seems that those who consume more caffeine are better able to tolerate it, the investigators believe.

Caporaso said:

“It turns out that your liver, more than your brain, determines daily caffeine intake. You might think – ‘I drink caffeine to feel good, or not to feel bad’ – but that, in turn, is established by how fast your liver breaks down the caffeine. If your liver breaks it down very rapidly, then likely you drink more.”

The researchers, led by a team from the Harvard School of Public Health, examined the genes of 47,341 middle-aged individuals of European descent in the USA. They all completed a questionnaire which included details on their coffee, tea, soda and chocolate intake. Those with the specific gene version (“high-consumption variant”) tended to drink on average 40mg more caffeine per day – equivalent to a can of coke or a third of a cup of coffee – compared to those without the genetic variant (termed “low-consumption variant”).

The scientists also found that 90% of adult Americans consume caffeine regularly in liquid or solid form, while 80% of caffeine consumers drink coffee.

The team was astonished to find two associated caffeine genes after sifting through over 300,000 genetic markets. And to “find them both holding hands was amazing.” One gene regulates the other.

Caporaso wrote:

“Caffeine is the most commonly consumed substance with important psychoactive properties. Just try skipping your coffee for two days! Knowing the specifics of the genetic influence on its disposition will jumpstart lots of studies.”

The authors believe their findings will help further studies that look into the physical effects of caffeine, including anxiety, sleep, physical activity, as well as some medication conditions. Further research is needed into determining why caffeine affects people in different ways, and how it impacts on heart disease and diabetes.

“Genome-Wide Meta-Analysis Identifies Regions on 7p21 (AHR) and 15q24 (CYP1A2) As Determinants of Habitual Caffeine Consumption”
Cornelis MC, Monda KL, Yu K, Paynter N, Azzato EM, et al. (2011)
PLoS Genet 7(4): e1002033. doi:10.1371/journal.pgen.1002033

Written by Christian Nordqvist