Once a year, not often. My friend gives it once a quarter (his blood is thick).
The total blood volume of a normal person accounts for about 8% of the body weight, and a person weighing 60 kg has about 4800 ml of blood. Donating 200 ml of blood at a time only accounts for 1/20 of the whole body blood volume, and will not affect the normal blood circulation. Moreover, the life cycle of red blood cells is about 120 days in plain area and about 80 days in plateau area. Blood donation at intervals of not less than 6 months is harmless to health. In normal blood circulation, 80% of human blood participates in circulation to ensure normal physiological function, and the remaining 20% is stored in organs such as liver, spleen and subcutaneous capillaries. When the body needs it, this part of the blood will be released immediately and added to the blood circulation. Therefore, donating no more than 400 ml of blood at a time will not cause harm to the body.
Not only is it harmless, but it is also good for your health:
First, it can prevent and relieve hyperviscosity.
Scientists have studied the relationship between blood and blood donation by using hemorheology and hemodynamics, and found that adhering to long-term moderate blood donation, especially donating tangible components such as red blood cells and platelets, can obviously reduce blood viscosity, speed up blood flow and increase cerebral blood flow, thus alleviating or preventing hyperviscosity, making people relaxed, clear-headed and energetic.
Second, it can prevent and reduce the occurrence of cardiovascular and cerebrovascular diseases.
Third, male blood donation can reduce the occurrence of cancer.
Fourth, it can promote and improve mental health.
Fifth, it can prolong life.
Disposable blood collection equipment completely avoids the way of blood infection.
Besides, I appreciate and admire everything you have done!