Coffee can really boost your energy. Coffee refreshing effect mainly comes from the caffeine. Caffeine can agitate caffeine is fat-soluble, can enter the brain, in the brain, caffeine antagonism adenosine A receptor, adenosine A receptor is mainly distributed in the acetylcholine neurons. Therefore, caffeine is equivalent to the excitation of acetylcholinergic neurons, this part of the neurons are mainly related to memory, association, learning, etc., so there is a definite “refreshing” effect. The amount of caffeine in coffee varies depending on the type of coffee beans and how the coffee is made. The caffeine content in a cup of about 250 ml of freshly brewed black coffee is about 90-200 mg, so 1 ml of black coffee contains about 0.4-0.8 mg of caffeine, and it is safe for the human body to consume up to 300 mg of caffeine per day. The exact amount of coffee needed to produce a refreshing effect is not the same for everyone and depends largely on caffeine tolerance. Caffeine can begin to work in the body in less than an hour and the effects wear off within 3 to 4 hours. Specialized populations such as pregnant women and the elderly have a longer duration of action. Consumption of caffeine does not reduce the amount of sleep needed, so the body may feel more tired after the effect. It is recommended to consume coffee in moderation, not in excess, otherwise it may easily lead to panic, insomnia and other side effects. For patients with underlying diseases such as gastroesophageal reflux, gastritis, gastric ulcer, etc., it is necessary to strictly control the intake of coffee and to avoid drinking strong coffee.