Did you ever wonder why some people can drink a gallon of coffee a day, while others feel shaky and unwell after only one cup? Why is it that some find themselves in an addictive relationship with coffee, while others are content with a simple cup of joe each morning?

The answer may lie in our genes.

A new study published in Scientific Reports analyzed the genetic makeup of two different Italian village populations while also conducting surveys about their coffee intake. The villagers who reported drinking fewer cups of coffee a day demonstrated a variant of the PDSS2 gene. To check their work, the researchers conducted a similar study in the Netherlands, and while the gene variant's influence over coffee consumption was weaker, it was still present. Researchers did acknowledge that coffee culture may have also played a part, including cup size and the types of coffees popular in the countries.

So what does PDSS2 do to influence why some people chug coffee through the day and others need only a cup or two? The variant has some impact on the ways in which caffeine is metabolized by the body, mainly slowing it down. The longer it takes to metabolize caffeine, the longer its effects last. This ends up extending the duration of the coffee fix for every cup.

These findings correspond with research published in 2014 in Molecular Psychiatry that identified six gene variations linked to coffee consumption to add to a previously known two. This large study had 120,000 participants who answered questionnaires on their coffee consumption and allowed their DNA to be analyzed.

Two of the genes they discovered were related to the metabolism of caffeine, and two others were related to the "reward" effect we get from caffeine. How our body metabolizes caffeine, and how much it takes for us to get a sense of reward from drinking it surely can lean us one way or another in our coffee consumption, so those make perfect sense. The most interesting gene discovery they found was that two genes related to our glucose and lipid metabolism were also related to our coffee consumption, which was a surprise to the researchers.

This story was originally published in October 2014 and has been updated with new information.