Anaemia (Greek, “bloodlessness”), blood condition involving an abnormal reduction in the number of red blood cells (erythrocytes) or in their haemoglobin content. Red blood cells are the means by which oxygen is carried to the various parts of the body. People who are anaemic develop symptoms caused by the inadequate delivery of oxygen to their body tissues. The condition is far more common in women than in men. There are three primary causes: (1) reduced production of red blood cells, which may result from deficiency in nutrients or hormones, or from disease or other conditions; (2) excessive destruction of red blood cells, often a hereditary problem; and (3) excessive blood loss, such as that caused by gastrointestinal ulcers, heavy menstrual periods, or overdose of aspirin. The most usual symptoms of anaemia are pallor, shortness of breath, low vitality, dizziness, and digestive disorders.

The most common type of anaemia is iron-deficiency anaemia, which occurs when the body’s need for iron increases, as during certain periods of childhood and in pregnancy, or when there is insufficient iron in the diet. Pernicious anaemia, a chronic ailment that mostly affects people over 40, is a result of vitamin B₁₂ deficiency. Rather than a diet deficient in the vitamin, this is usually caused by intestinal malabsorption, resulting in decreased B₁₂ uptake. Sickle-cell anaemia is the result of a hereditary defect in the synthesis of haemoglobin. Aplastic anaemia occurs when there is severe reduction in red blood corpuscles, and when the bone marrow is unable to regenerate them. Ionizing radiation is one possible cause.

Past treatment of the condition has included removal of the spleen, repeated transfusions of blood, and a diet featuring beef or calf’s liver. Transfusions are still used in cases of acute blood loss; iron supplements for iron-deficiency anaemia and injections of vitamin B₁₂ for pernicious anaemia are often effective. Synthetically manufactured erythropoietin (normally produced by the human kidney) is now used to stimulate the production and growth of red blood cells. Other therapy focuses on curing the underlying causes of the nutritional or hormonal deficiency. Blood transfusions and, increasingly, bone marrow transplants, are necessary forms of treatment for aplastic anaemia patients.