Caffeine and Drinking Coffee at Night May Mess Up Your Internal Clock

Drinking caffeine can disrupt your sleep. But did you know that drinking caffeine in the evening also delays the internal circadian clock that tells us when to get ready for sleep and when to prepare to wake up? That's exactly what scientists found in this latest study.

"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 Kenneth Wright, one of the researchers, in a news release. "It also provides new and exciting insights into the effects of caffeine on human physiology."

The researchers actually recruited five human subjects, three females and two males, who went through an experiment; they were tested under four conditions, including low light and a placebo pill, low light and the equivalent of a 200-milligram caffeine pill, bright light and a placebo and bright light and the caffeine pill.

So what did they find? Those who took the caffeine pill under low-light conditions had a roughly 40-minute delay in their nightly circadian rhythm. The magnitude of the delay from the caffeine does was about half that of the delay induced in test subjects by a three-hour exposure to light.

Those exposed to bright light without the caffeine had a delay of 85 minutes, and those with the caffeine had a delay of 105 minutes.

The results may explain why caffeine-drinking "night owls" go to bed later and wake up later. The results may also have implications for the treatment of some circadian sleep-wake disorders.

The findings are published in the journal Science Translational Medicine.

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