Coffee Puts a Break in Your Circadian Rhythm

You might want to nix that 5:00 p.m. end-of-the-workday coffee that you always reach for. The University of Colorado in Boulder, in conjunction with Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England, recently published a study in Science Translational Medicine that shows how caffeine can actually alter your circadian rhythm.

How the study was conducted

Although it’s no secret that coffee can keep you awake, the research reveals what caffeine actually does to the body; it essentially slows down the internal clock in your cells, causing you to stay up later in the night.

The study, led by Kenneth Wright, involved five people who were kept in an area at CU Boulder’s Sleep and Chronobiology Laboratory for 49 days. The participants were placed in one of the following settings: under low light conditions with a caffeine pill, under low light conditions with a placebo pill, under bright light conditions with a caffeine pill, and under bright light conditions with a placebo pill. The varying levels of light were included in the study because light is known to affect the body’s circadian rhythm. Although it is a natural, biological process, artificial light tricks our bodies into thinking it is still bright out, which can cause us to want to stay up.

In order to gather data on our internal clocks, researchers took samples of everyone’s saliva, which contains melatonin, a substance involved in the synchronization of the circadian rhythms of physiological functions, such as sleep timing. The level of melatonin increases when the body believes it’s time to sleep, and decreases when it’s time to wake up.

From the test, the researchers were able to determine that the circadian rhythms of the participants who took the caffeine pill under low lighting conditions were pushed back 40 minutes. With lighting and caffeine, the clock was set back another 65 minutes, for a total of 105 minutes of disrupted time.

The study also concentrated on how caffeine affects other areas of the body. Researchers, for example, were able to determine that caffeine actually blocks adenosine, which is a neurotransmitter that usually suppresses the arousal of a person and helps the body prepare itself for sleep.