Why doesn't donating blood affect your health?

Blood is the source of life and an indispensable substance in medical rescue activities. At present, medical [clinical] blood can only come from healthy people. Under normal circumstances, a person's total blood volume is about 8% of his body weight, that is to say, a person weighing 50 kg has about 4 kg of blood, with a total volume of 4000 ml. Of these blood, only 80% generally participates in the blood circulation in the body, performing the duties of transporting oxygen and nutrients and resisting bacterial invasion, and the remaining 20% is stored in organs such as liver and spleen, which are called "blood banks" of the human body. When people are engaged in labor, strenuous exercise or a small amount of blood loss, blood will be immediately replenished into the blood circulation. The basic components of blood are red blood cells, white blood cells, platelets and plasma, and about half of blood is plasma. All blood components have a certain life span, red blood cells are about 120 days, white blood cells are 7 ~ 10 days, and platelets are about two weeks. Every moment, a certain number of blood cells die, and at the same time, a corresponding number of blood cells regenerate, thus maintaining the physiological balance of blood. The continuous metabolism of blood components is the basis of blood existence. Scientific research shows that a blood loss does not exceed 10% of the total blood volume, which will not affect health. On the contrary, scientific and reasonable blood donation can also stimulate the hematopoietic function of bone marrow, accelerate hematopoiesis, reduce the viscosity of blood, promote blood metabolism, enhance human immunity and prevent certain diseases. At most three weeks after blood donation, the blood in the body can completely return to normal level. For example, some people think that blood donation will hurt your vitality, become addictive, make you fat and affect your fertility. There is no scientific basis.