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Drinking the equivalent of a double espresso three hours before going to sleep can turn back our body clock by around an hour, a finding that could have important implications for a range of sleep conditions, a new study has revealed.

Researchers has shown that caffeine directly affects the body clock by delaying a rise in the level of the hormone melatonin, the main sleep hormone released by the body to make us feel sleepy.

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To discover the effect caffeine has on the body clock, the US scientists from the University of Colorado studied five people to see when melatonin starts to appear in saliva. Each person lived in the lab for 49 days without a clock or any knowledge of 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 (the bright light acted as a control as it also delays the human circadian clock) to find out when the surge in melatonin occurred.

Dr. John O’Neill joint lead researcher at UK MRC Laboratory of Molecular Biology,  the findings 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. 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.

The body clock, or circadian rhythm, operates in every single cell in the body, turning genes on and off at different times of the day to allow us to adapt to the external cycle of night and day. Disruption of this, from shift work or regular jet lag, can increase the risk of various cancers, heart disease, type 2 diabetes and neurodegenerative disorders such as Alzheimer’s.

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