Coffee (and also tea, but in smaller quantities) contains caffeine. Caffeine is a stimulant of the central nervous system, accelerates heart ripple, increases urination, narrows blood vessels. The caffeine content of 150-200 mg per kilogram of body weight is a lethal dose (one cup of espresso contains about 65 mg of caffeine). The maximum caffeine content in the blood is 45-60 minutes after administration.
And so, how does caffeine work and what is its hidden danger (except for the lethal dose). By its structure, caffeine is similar to adenosine. Adenosine is an integral part of ATP (adenosine triphosphate). ATP in all living organisms plays the role of universal battery and carrier of "energy". The principle is - ATP consists of adenosine and three residues: phosphoric acid. End phosphorus residues, under the influence of enzymes, splitting off adenosine secrete heat (scientific language "energy"). As a result, we say, we walk, we read, we do everything that pleases and what is necessary for our life activity: "we are doing work." Gradually, the reserves of ATP are consumed and adenosine accumulates in our body. Adenosine, binding to adenosine receptors, tells our brain about a large amount of adenosine. The brain is reading it and making conclusions, we have spent ATF ("energy") reserves and therefore we need rest to accumulate new reserves of ATP. As a result, we feel fatigue and we are sleepy.

After drinking coffee, we get a completely different effect. Cheerfulness, the feeling that we still have strength. All this is because caffeine is very similar to adenosine (Figure 1). Therefore, having got into the body, caffeine as a key, comes to adenosine receptors, which interact with adenosine. But caffeine is not adenosine, although it is very similar, and does not report the necessary information to the brain, but it occupies the adenosine receptor. Plus, caffeine contributes to the production of adrenaline. As a result, there are no reserves of "energy" (ATP) in the body, but they will be vigorous and ready for action. Our body begins to work on wear (using reserve sources or can take from other sources than to disrupt their work). In this and the danger. Caffeine is not a source of "energy," but a snag. To consume large amounts of coffee instead of food is dangerous for the body. The constant high intake of caffeine on an empty stomach can lead to physical and nervous exhaustion.
Take care of yourself! Drinking a cup of coffee, eat a bun or a sandwich or chocolate or that you like more ...