A double shot of espresso can rewind the body clock to an hour and could help fight jet lag for those travelling to the west, scientists claim.

Published in the journal Science Translational Medicine, scientists from University of Colorado and the Medical Research Council in Cambridge explain how caffeine actually affects the circadian rhythm.

"This is the first study to show that caffeine, the mostly widely used psychoactive drug in the world, has an influence on the human circadian clock," said University of Colorado's Department of Integrative Physiology Professor Kenneth Wright.

According to the study, caffeine can trick the body into thinking it's an hour earlier in the day - making it an effective way to deal with time zone changes, for example, when you are travelling from London to New York.

"The effect of caffeine on sleep and wakefulness has been long established, but its impact on the underlying body clock has remained unknown," said MRC Laboratory of Molecular Biology joint lead researcher Dr John O'Neill. "These findings could have important implications for people with circadian sleep disorders, where their normal 24 hour body clock doesn't work properly, or even help with getting over jet lag."

O'Neill adds this explains why people have caffeine-induced insomnia aside from the chemical-stimulating factor that caffeinated drinks contain.

"Our findings also provide a more complete explanation for why it's harder for some people to sleep if they've had a coffee in the evening - because their internal clockwork thinks that they're an hour further west," he said. "By understanding the effect caffeinated drinks have on our body clock, right down to the level of individual cells, gives greater insight into how we can influence our natural 24 hour cycle - for better or for worse."

As much as it helps travelers going to the west, caffeine, however, does the other way around to those travelling to the other side.

As Wright added, "findings suggest that if you take caffeine at the wrong time, it could make your jet lag on an eastward trip worse."