According to a report recently published in Science Translational Medicine, researchers may have discovered the key to how caffeine consumption can disrupt the body’s clock: its affects on melatonin.
It appears that drinking the equivalent of a double espresso three hours before bedtime can turn back the clock by an hour, by delaying an increase in melatonin levels. The melatonin hormone makes people feel sleepy and can be released upon certain triggers (e.g., exposure to dim lights).
The body’s clock operates in every cell in the body. It turns genes on and off at different times, which allows humans to adapt to external night and day cycles.
The report describes an experiment where five people were invited to live in a lab for 49 days without any exposure to external light or clocks to inform them if it was day or night.
Participants were exposed to dim lighting and bright lighting. Bright lighting acts as a stimulus that extends the circadian (24-hour) phase. They were either given caffeine (an amount equivalent to a double espresso) or a placebo three hours before they went to sleep. Each participant’s saliva was tested three hours later to determine how much melatonin was produced.
Researchers discovered that when caffeine was given, melatonin levels increased about 40 minutes later compared to the placebo, representing a shift approximately half as long as one caused by bright light.
Caffeine increases the levels of cyclic adenosine monophosphate (cAMP), which is an important intracellular messenger molecule.
The cAMP molecule is important when it comes to the inner workings of the body clock, so researchers have concluded that there is a link between caffeine’s biochemical effects and its role in delaying the circadian clock. Lowering the levels of the cAMP molecule leads to a decrease in the delay that caffeine normally produces.
The study’s lead researcher Dr. John O’Neill suggests that these findings could be important for people with circadian sleep disorders.
Sources for Today’s Article:
Brazier, Y., “How an Evening Coffee Can Disrupt Our Body Clock,” Medical News Today web site, September 18, 2015; http://www.medicalnewstoday.com/articles/299638.php.
Burke, T., et al., “Effects of caffeine on the human circadian clock in vivo and in vitro,” Science Translational Medicine 2015, doi: 10.1126/scitranslmed.aac5125.