Megaloblastic anemia is anemia caused by disorders of deoxyribonucleic acid synthesis, mainly caused by a lack of vitamin B12 or folic acid in the body, but can also be caused by acquired DNA synthesis disorders such as hereditary or drug. The main causes of folic acid deficiency are as follows: First, insufficient intake. Folic acid can be lost when food is lacking fresh vegetables, overcooked or pickled. Ethanol can interfere with the metabolism of folic acid, and alcoholics often have folic acid deficiency. Also inflammation, tumors, and surgically removed patients can lead to insufficient absorption of folic acid. Second, it needs to be increased. The need for folic acid increases in pregnant women, growing children and adolescents, as well as in patients with chronic recurrent hemolytic leukemia, tumors, and hyperthyroidism. If the supplementation is not enough, folic acid deficiency can occur. Third, the influence of drugs. For example, methotrexate and etanercept can inhibit the production of folic acid. The etiology of vitamin B12 deficiency also includes: 1. Decrease in intake. The storage of vitamin B12 in the human body is about 2-5mg, and the daily requirement is 0.5-1µg, so vitamin B12 deficiency will not occur in normal people. Older people and patients with gastrectomy have reduced gastric acid secretion and can have impaired absorption of vitamin B12; 2. Deficiency of internal factors. It is mainly seen in patients with atrophic gastritis, post-total gastrectomy, patients with pernicious anemia, patients with severe pancreatic exocrine deficiency, which can also lead to vitamin B12 malabsorption, or the presence of abnormally high concentrations of bacteria and parasites in the small intestine, which can also affect the absorption of vitamin B12. The above diseases that cause folic acid deficiency, or vitamin B12 deficiency, can all cause megaloblastic anemia.