London - It's no secret that a coffee before bedtime can destroy your chances of a decent night’s sleep.
But we can no longer pin the blame entirely on the alertness-boosting effects of caffeine.
Drinking a strong coffee in the evening can produce the same effect as jet lag – by fooling our body into thinking we are in a completely different time zone.
Researchers say the beverage slows down our internal clock, making our body think it is around an hour further west than it actually is. Some 200mg of caffeine – the amount found in some coffees – is enough to convince the brain it is a whole time zone behind, experts found.
As a result coffee drinkers are likely to find it harder to get to sleep – but also find it harder to get up in the morning, too.
The British and US research appears to reinforce the advice to avoid caffeine in the evening. But it could also shed new light on the effects of a chaotic body clock, which has been linked to a host of ills from cancer and heart disease to diabetes and Alzheimer’s.
Researcher John O’Neill, of the Medical Research Council in Cambridge, said: “This adds a new layer to understanding what caffeine does. Not only does it stop you from going to sleep, it is delaying your biological clock, so when you do finally go to sleep you want to sleep in longer because you are caffeine-lagged.”
As part of the study, researchers looked at the effect of a pill containing 200mg of caffeine on a group of men and women. The group were exposed to different levels of light at bedtime as they stayed in a windowless laboratory for seven weeks without clocks.
A mug of instant coffee contains around 100mg of the stimulant and a cup of tea has 50mg. The average single espresso, the base of many high street coffees, contains 80mg of caffeine – although research has shown that some pack more than 200mg in a single shot.
Results showed that pill delayed the onset of melatonin, a hormone produced by the body in the evening that makes us feel sleepy.
The combination of caffeine and a dimly-lit bedroom caused an average lag of 40 minutes – roughly the equivalent of crossing one time zone when flying west. In some cases the body clock went back two hours.
The overall effect was the same as being exposed to bright light for three hours when trying to get to sleep.
Writing in the journal Science Translational Medicine, researchers said the results mean caffeine could even be used to help travellers avoid jet lag itself.
Daily Mail