Why does caffeine make me sleep better

What it means: being able to drink coffee and sleep

Vienna - Everyone knows the situation after dinner. When asked "Coffee?" there are two answers. One: "Yes, definitely," the other: "No, for God's sake, if I have a coffee now, I won't close my eyes all night."

The fact is: "Caffeine is a pharmacologically active substance," says Markus Zeitlinger, Head of the University Clinic for Clinical Pharmacology at Med-Uni Vienna, the effect can be measured objectively in tests that examine muscle performance or attention. Caffeine is a stimulant and makes receptors jump on. This has the sensory effect of making you feel more alert, but it can also have motor effects, such as actual tremors at very high doses, for example.

So far, so well known. But: The body has degradation systems for all substances that come from the outside in order to restore the normal state of the organism. The enzyme system cytochrome P450 1A2 (CYP1A2) is responsible for caffeine. It is one of two dozen regulatory rails in the body that can be thought of as a kind of sewage treatment plant. If caffeine could not be broken down, "one would be awake forever with one dose of caffeine," says Zeitlinger, but the enzyme systems responsible can vary greatly from person to person. How pronounced CYP 1A2 is depends on the basic genetic constellation.

Highly flexible and changeable

Due to these genetic differences, called polymorphisms, the activity of the enzyme can fluctuate between ten and 200 percent. Accordingly, people with high enzyme activity break down coffee so quickly that the caffeine does not seem to have any effect. Zeitlinger calls it "Fast Metabolizer". This group can fall asleep wonderfully after an espresso - in contrast to the "slow metabolizers", which keep the caffeine and its effects in the body for much longer.

The enzyme system CYP1A2 is not only responsible for breaking down caffeine, however, a whole range of drugs are metabolized via this route, such as a number of painkillers, antidepressants, local anesthetics (the syringe at the dentist, for example), immunosuppressants or cancer drugs. "An analogy between the effects of coffee and medication is not possible in this simple form," emphasizes Zeitlinger and also explains why. "The organism is a complex, sophisticated system that can also be changed by external influences," he says, referring to the habituation effect.

Regardless of the breakdown of the caffeine, the receptors in the body get used to high doses of caffeine. The stimulating effect decreases as a result. Caffeine is also mildly addictive. Many notice this in the withdrawal symptoms that occur when not using caffeine, such as headaches or irritability. In addition, the human body is subject to circadian rhythms: Coffee in the morning can have a different effect than coffee in the evening, "because the general state of excitement varies throughout the day," says Zeitlinger. Like much in life, the effects of caffeine are also a matter of dose. The biggest misunderstanding is to believe that a cup of espresso contains more caffeine than a mug of filter coffee. "People often drink gallons of coffee, compared to a small espresso that contains a much smaller dose."

No worries

In addition, the body's breakdown systems are exposed to many different factors and influence each other - "inhibition and induction", Zeitlinger calls it. There are, for example, between nicotine and caffeine. Those who smoke break down caffeine more quickly, so smokers can drink more coffee and smokers need more coffee to feel the stimulating effect. Grilled meat also has the same effect. "It is believed that the substances produced during grilling can influence the CYP1A2 enzyme line," says Zeitlinger, although, interestingly, this is also the case with cabbage and broccoli.

If, on the other hand, you want to stop the CYP1A2 breakdown system and thus increase the effect of the coffee, you could at least theoretically achieve this effect with grapefruit juice. It is an inhibitor, just like St. John's wort, which is used as a herbal remedy for depression. "However, permanent exposure would be necessary," says Zeitlinger - nobody who eats a steak needs to fear that the espresso will not work afterwards.

When it comes to drugs, the same applies: "Nobody who cannot sleep after coffee needs to be genetically examined," emphasizes Zeitlinger, because such a test would have no significance for effectiveness. (Karin Pollack, November 4, 2017)