Blood consists of a liquid called plasma and cells. Floating within the plasma are three types of blood cells:
• White blood cells (leukocytes). These blood cells fight infection.
• Platelets. These blood cells help your blood clot after a cut.
• Red blood cells (erythrocytes). These blood cells carry oxygen from your lungs, via your bloodstream, to your brain and the other organs and tissues. Your body needs a supply of oxygenated blood to function. Oxygenated blood helps give your body its energy and your skin a healthy glow.
Red blood cells contain hemoglobin — a red, iron-rich protein that gives blood its red color. Hemoglobin enables red blood cells to carry oxygen from your lungs to all parts of your body, and to carry carbon dioxide from other parts of the body to your lungs so that it can be exhaled.
Most blood cells, including red blood cells, are produced regularly in your bone marrow — a red, spongy material found within the cavities of many of your large bones. To produce hemoglobin and red blood cells, your body needs iron, other minerals, protein and vitamins from the foods you eat.
Causes of common types of anemia
When you're anemic, your body produces too few healthy red blood cells, loses too many of them or destroys them faster than they can be replaced. Common types of anemia and their causes include:
• Iron deficiency anemia. This common form of anemia affects about 1 to 2 percent of adults . The cause is a shortage of the element iron in your body. Your bone marrow needs iron to make hemoglobin. Without adequate iron, your body can't produce enough hemoglobin for red blood cells. The result is iron deficiency anemia.
• Vitamin deficiency anemias. In addition to iron, your body needs folate and vitamin B-12 to produce sufficient numbers of healthy red blood cells. A diet lacking in these and other key nutrients can cause decreased red blood cell production. Additionally, some people are unable to effectively absorb B-12.
• Anemia of chronic disease. Certain chronic diseases — such as cancer, HIV/AIDS, rheumatoid arthritis, Crohn's disease and other chronic inflammatory diseases — can interfere with the production of red blood cells, resulting in chronic anemia. Kidney failure also can be a cause of anemia.
• Aplastic anemia. This very rare, life-threatening anemia is caused by a decrease in the bone marrow's ability to produce all three types of blood cells — red blood cells, white blood cells and platelets. Many times, the cause of aplastic anemia is unknown, but it's believed to often be an autoimmune disease.
• Anemias associated with bone marrow disease. A variety of diseases, such as leukemia and myelodysplasia, a preleukemic condition, can cause anemia by affecting blood production in your bone marrow. The effects of these types of cancer and cancer-like disorders vary from a mild alteration in blood production to a complete, life-threatening shutdown of the blood-making process. Other cancers of the blood or bone marrow, such as multiple myeloma, myeloproliferative disorders and lymphoma, can also cause anemia.
• Hemolytic anemias. This group of anemias develops when red blood cells are destroyed faster than bone marrow can replace them. Certain blood diseases can cause increased red blood cell destruction. Autoimmune disorders can cause your body to produce antibodies to red blood cells, destroying them prematurely. Certain medications, such as some antibiotics used to treat infections, also can break down red blood cells.
• Sickle cell anemia. This inherited and sometimes serious anemia, which more commonly affects people of African, Arabic and Mediterranean descent, is caused by a defective form of hemoglobin that forces red blood cells to assume an abnormal crescent (sickle) shape. These irregular-shaped red blood cells die prematurely, resulting in a chronic shortage of red blood cells.
• Other Anemia’s. There are several other, rarer forms of anemia, such as thalassemia and anemias caused by defective hemoglobin.
Sometimes, no cause of anemia can be identified.