Drinking coffee at night may push back your body clock and give you jetlag.

Image: (Ramain/iStockPhoto)

Drinking a double espresso at night may not only keep you awake longer, but could also push you into a whole new time zone, new research suggests.

Night-time caffeine intake delays our body clock by about 40 minutes, suggests a study published in Science Translational Medicine.

“Everyone knows caffeine promotes wakefulness and disturbed sleep,” lead author Professor Kenneth P Wright Jr of the Sleep and Chronobiology Laboratory at University of Colorado Boulder said.

“But there’s another way that caffeine is affecting our physiology that we really hadn’t considered before.”

It is well known that caffeine stimulates brain chemicals that keep us awake and blocks those that promote sleep.

But previous research in animals has suggested caffeine may also interact with our circadian clock — which affects not just our brain, but the rest of our body, including liver, fat and muscle cells.

When we are not in sync with our body clock, we feel sleepy and our body is not primed for eating or being physically active.

The woozy feeling we have with jetlag is a case in point.

“In jetlag, not only your brain is in a different time zone but your liver is too,” Professor Wright said.

Double espresso versus bright light

Professor Wright and colleagues studied what happened to people’s body clocks when they were exposed to caffeine to the equivalent of a double espresso coffee at night, three hours before their usual bed time.

They compared this to what happened when people were exposed to bright light at night time, which is already known to delay the body clock.

To measure body clock time, the researchers tested saliva levels of melatonin, a key hormone involved in regulating the body clock. A rise in melatonin levels coincides with us feeling sleepy.

“We found caffeine was able to delay the body clock by about 40 minutes, compared to placebo,” Professor Wright said.

“It’s not just promoting acute wakefulness, but it’s changing the whole timing of your entire system.

“In this case, caffeine is pushing you into another time zone.”

The researchers found the effect of caffeine on the body clock was not as strong as the effect from night-time exposure to bright light, but was still significant.

“It has an effect that is about half of what we see with light,” Professor Wright explained.

He said the findings suggested chronic use of caffeine to stay up late will train the body clock to be delayed and will make it difficult for people to get up at the usual time, without suffering jetlag-type effects.

Small but sensitive study

While the researchers only tested five people over the course of 49 days, each person was exposed to all the different study conditions — which meant they were compared to themselves.

The study was double blind placebo controlled, so neither researchers nor subjects knew if they were consuming a placebo or caffeine.

“Using that sensitive design allowed us to test fewer people and really determine what the impact was of the different treatments that we tested,” Professor Wright said.

The researchers were also able to show that caffeine bound to an adenosine receptor in human cancer cells, which boosts cyclic adenosine monophosphate levels which affect the timing of the cell’s clock.

But further research was needed to check if the circadian clock of other human cells — for example liver cells — were really also affected by caffeine, Professor Wright said.

This article was originally published on the ABC. Read the original article here.

Do you find coffee affects your body clock?