Want to cheat jet lag? A drink of coffee could do the trick

Caffeine affects the body clock by delaying a rise in the level of melatonin, the main sleep hormone released by the body. Photo / iStock

Drinking coffee in the evening can turn back the body clock and could help fight jet lag - but only for travellers heading west, scientists believe.

Coffee appears to trick the body into thinking that it is around an hour earlier in the day, reactiviating bodily functions that should be powering down in the evening.

For people travelling west on a plane who need to push back their body clocks, drinking a double espresso when changing time zones is likely to help with jet lag, said scientists from the Medical Research Council in Cambridge and the University of Colorado. But those travelling east may make jet lag worse by drinking coffee.

Dr John O'Neill, the joint lead researcher at the council's Laboratory of Molecular Biology, said: "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.

"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."

The researchers showed that caffeine affects the body clock by delaying a rise in the level of melatonin, the main sleep hormone released by the body. The US team studied five people to see when melatonin started to appear in saliva. Each person lived in the lab for 49 days without a clock or external light to tell them if it was night or day.

They were then given caffeine, the equivalent of a double espresso, or a placebo three hours before they went to sleep and were exposed to dim or bright light - which also delays the human circadian clock - to find out when the surge in melatonin occurred. In those who were given the caffeine, their melatonin levels rose on average 40 minutes later than those given the placebo.

To understand the mechanisms underpinning this, the UK-based researchers added caffeine to human cells in the lab and found that it also delayed their built-in circadian clock. Disruption of the circadian rhythm, from shift work or regular jet lag, can increase the risk of cancers, heart disease, type 2 diabetes and neurodegenerative disorders such as Alzheimer's. The research is published in the journal Science Translational Medicine.