Researchers scanned genetic variations in over 40,000 individuals to search for links with high caffeine intake. And they found two stretches of DNA associated with high intake of tea, coffee, chocolate, softdrinks and other caffeine sources.

Study author Dr Neil Caporaso of the National Cancer Institute in Maryland, said people with the high consumption genetic variation consume more caffeine -- about 40 mg -- or a third of a cup of coffee or a can of cola -- than others.

"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," he was quoted as saying by the 'BBC'.

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.

The study's co-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. "For caffeine at last we have been able to find some genetic factors."

The findings have been published in the 'PLoS Genetics' journal.