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Drinking coffee should not be excessive to understand the two sides of coffee.

Published: 2026-08-25 Author: World Gafei

Last Updated: 2026/08/25, For a long time, people have said that coffee contains caffeine, so coffee is refreshing; after drinking coffee, you can't sleep at night. However, I have heard people say from time to time that it is useless for me to drink coffee, so I still fall asleep. Some even said: contrary to my expectations, I still feel sleepy after drinking coffee. In view of this, recently, some scientists have been restudying coffee.

For a long time, people have said: "Coffee contains caffeine, so coffee is refreshing; after drinking coffee, you can't sleep at night." However, from time to time, people say, "it's useless for me to drink coffee, so I'm still fast asleep." Some even said, "contrary to my expectations, I still feel sleepy after drinking coffee." In view of this, recently, scientists continue to re-study coffee, and the results can no longer be explained by "coffee refreshing". For example, American scientists conducted various experiments on 80 subjects aged from 18 to 40. These subjects were divided into four groups. The first group received a placebo drink with no effect, and the other three groups received different doses of coffee. Then a computer program was used to calculate and show the subjects' stress response ability and the time needed to achieve excitation. the results showed that the group with the least dose of coffee had the strongest stress response ability and the shortest time to achieve excitement. The two groups that received more coffee were as responsive as or weaker than those with the least dose, and took longer to get excited-close to what the scientists had expected: a cup of coffee would be enough.

Another experiment showed that people who drank coffee and alcohol did not have a refreshing effect on them. So experts warn: don't fight your drunkenness with a pot of coffee, or you'll be lucky to get into the subway car and get off at the right station.

Adults with attention deficit syndrome, in particular, have a strange reaction after drinking coffee: much quieter than usual. If these people have had coffee before an operation, they should explain it to the anesthesiologist, as this cup of coffee may cause the patient to wake up from anesthesia and return to a slight sleep.

One neurologist even advises some headache patients to drink a cup of espresso before going to bed, so that they can easily fall asleep. Coffee plays a role in dilating problematic cerebral vessels here. For some people who do not have headaches, coffee can also play a hypnotic effect. According to some older people, drinking a cup of coffee before going to bed does not affect sleep at all.

There are two reasons why coffee has a function contrary to traditional belief. One is the special mode of action of coffee. Caffeine in coffee blocks a substance called adenosine, which inhibits the secretion of excitatory neurotransmitters (such as dopamine or epinephrine). But coffee can also increase the cross section of blood vessels and respiratory tract temporarily, so coffee lowers blood pressure and respiratory rate at first (many people feel that coffee has a calming effect), but after 15 to 20 minutes, the brain begins to get excited. so if you go to bed after drinking coffee for a long time, you are likely to be sleepless all night. Another reason has to do with the biological principle of "environmental stability in the body". Every organism has to create a "balance of force" in the body, and some people suffer from attention deficit disorder or are already stimulated by alcohol. if you use coffee, it will no longer work; on the contrary, it is possible for the body to use emergency braking.

In addition, the effect of coffee on attention and learning ability is not one-way, there is an idea that coffee is conducive to aimless learning, if you are reading a book easily while leisurely tasting the fragrant coffee, then a lot of what you read will be "injected" into the brain.

In fact, the two sides of coffee is not so absolute and accurate, but one thing should be kept in mind: do not overdo it.

Source: Xinmin Evening News (Shanghai)

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