How Coffee at Night Changes Your Body Clock

Ever wonder how drinking coffee at night can affect how you sleep?

New research conducted by Medical Research Council Laboratory of Molecular Biology in the U.K. and the University of Colorado suggests that caffeine consumption--the equivalent of a double espresso--three hours before bedtime can turn back a person's body’s clock by an hour by delaying the nightly rise in the level of the hormone melatonin.

The researchers invited five people to live in a lab for 49 days without a clock or any knowledge of external light to tell them if it was night or day. Participants were exposed to bright or dim light. Bright light, like caffeine, is known to be a stimulus that lengthens the circadian phase.

The participants were then given either caffeine - the equivalent of a double espresso - or a placebo three hours before going to sleep. Their saliva was then tested three hours later to see how much melatonin had been produced.

The results showed that when caffeine was consumed, melatonin levels rose around 40 minutes later than with the placebo. This represented a shift about half as long as what was caused by the bright light.

To confirm the results, a team of UK-based researchers added caffeine to human cells in a lab, and found the same results - the built-in circadian clock was delayed.

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Sourced from: Medical News Today, How an evening coffee can disrupt our body clock