Coffee addicts have an excuse for blaming their genes.
According to new research, genetic factors could explain why some people consume large amounts of caffeine.
US researchers scanned genetic variations in over 40,000 individuals to search for links with high caffeine intake.
They found two stretches of DNA associated with high consumption of tea, coffee, chocolate, soft drinks and other sources of caffeine.
The study is published in the journal PLoS Genetics.
Study author Dr Neil Caporaso of the National Cancer Institute, Bethesda, Maryland, US, said people with the high consumption genetic variation consume more caffeine - about 40mg - or a third of a cup of coffee or a can of cola - than other individuals.
He told the BBC: "There are hundreds of genes known for specific medical conditions - for dietary consumption we know very little.
"Now, for the first time, we know specific genes that influence the amount of caffeine that individuals consume."
The two stretches of DNA linked with high caffeine consumption contain two genes thought highly likely to be involved in the way the body processes caffeine.
One - CYP1A2 - has previously been shown to be involved in the body's break down of caffeine.
The second - AHR - helps regulate the first gene.
Study author, Dr Marilyn Cornelis of the Harvard School of Public Health, said there has always been some anecdotal evidence that everyone responds differently to caffeine, but most research has focused on environmental factors.
She said: "For caffeine at last we have been able to find some genetic factors."