Caffeine makes water fall asleep


Contrary to the well-known stimulating effect on humans, caffeine slows down the movement of water molecules. Researchers from the ESPCI in Paris and AMOLF in Amsterdam report this in a recent publication in the Journal of Physics Communications.

Illustration: Caffeine makes a water molecule (H2O) fall asleep.

A cup of coffee is known for its boosting effect. That is because it contains caffeine: the most commonly used stimulant in the world. It enjoys enormous popularity in beverages like coffee, tea, soft drinks, and energy drinks. Caffeine stimulates the central nervous system and boosts human performance by speeding up reaction times and by increasing alertness.

The human body consists for about 60% of water. On a molecular scale, water is very dynamic and water molecules dance with tiny ultrafast movements. Would they show the same behaviour in the presence of caffeine? The researchers from the ESPCI in Paris and AMOLF in Amsterdam asked themselves this question and performed experiments in the laboratory to find out. They used an advanced laser system to study the movement of water molecules and they discovered that the presence of caffeine slows down the movement of water molecules by a factor 5. They observed that one molecule of caffeine slows down 10 surrounding water molecules. Hence, in a cup of coffee, one in a thousand water molecules is slowed down.

The researchers also studied the effect of taurine, a frequently-used constituent of energy drinks. They discovered that taurine also puts the brake on water molecules; a single molecule of taurine slows down 4 water molecules. Energy drinks often contain both caffeine and taurine. Their combined effect causes 1 in 2000 water molecules to be slowed down.
However, do not worry in case you have just poured yourself a cup of coffee; to notice the effect of slow water, you need to drink so many cups of coffee that it becomes unrealistic. The consumption of one cup of coffee slows down only one in a million water molecules in the human body.

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Wilbert Smit,, +33 (0)1 40 79 46 70

Wilbert J. Smit, Eliane P. van Dam, Roberto Cota, and Huib J. Bakker, Caffeine and taurine slow down water molecules, Journal of Physics Communications 3, 2019.