Have you ever wondered why some people seem to constantly have a cup of coffee in their hands, while others only need a single cup in the morning? There may well be a genetic explanation, say US experts.
The scientists - from the Harvard School of Public Health and the University of North Carolina - believe they have discovered two genes that play a part in how the human body processes and breaks down coffee.
According to the experts, some people have a variant of one or both of the genes - called CYP1A2 and AHR - that causes high consumption of coffee, whereas others have the low-consumption variant (that is, they drink little to no coffee).
Writing in the journal PLoS Genetics, the scientists studied the genes of more than 47,000 people, comparing their version of one or the other genes with how much coffee they drank.
They discovered that the people who had the highest-consumption version of the CYP1A2 or AHR gene drank 40mg more caffeine than those who had the low-consumption genes. And though 40mg of caffeine doesn't amount to much (around the amount found in a third of a cup of coffee), the researchers insist their findings show that things like how much coffee we drink are dictated by our genetic makeup.
So if you have the low-consumption variant of either gene, thank yourself lucky - as it means your body processes coffee more slowly, so you don't need to top up very often to feel the energising effects of caffeine.
How much coffee do you drink in an average day?