Causes

Anemia can be due to a condition present at birth (congenital) or to a condition you develop (acquired). Anemia occurs when your blood doesn't have enough red blood cells.

This can happen if:

• Your body doesn't make enough red blood cells
• Bleeding causes you to lose red blood cells more quickly than they can be replaced
• Your body destroys red blood cells

What red blood cells do

Your body makes three types of blood cells — white blood cells to fight infection, platelets to help your blood clot, and red blood cells to carry oxygen from your lungs to the rest of your body and carbon dioxide from the body back to the lungs.

Red blood cells contain hemoglobin — an 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 to be exhaled.

Most blood cells, including red blood cells, are produced regularly in your bone marrow — a spongy material found within the cavities of many of your large bones. To produce hemoglobin and red blood cells, your body needs iron, vitamin B-12, folate and other nutrients from the foods you eat.

Causes of anemia

Different types of anemia have different causes. They include:

• Iron deficiency anemia. This most common type of anemia is caused by a shortage of 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.

  Without iron supplementation, this type of anemia occurs in many pregnant women. It's also caused by blood loss, such as from heavy menstrual bleeding; an ulcer in the stomach or small bowel; cancer of the large bowel; and regular use of some pain relievers that are available without a prescription, especially aspirin, which can cause inflammation of the stomach lining resulting in blood loss. It's important to determine the source of iron deficiency to prevent recurrence of the anemia.

• Vitamin deficiency anemia. Besides iron, your body needs folate and vitamin B-12 to produce enough healthy red blood cells. A diet lacking in these and other key nutrients can cause decreased red blood cell production. Some people who consume enough B-12 aren't able to absorb the vitamin. This can lead to vitamin deficiency anemia, also known as pernicious anemia.
• Anemia of inflammation. Certain diseases — such as cancer, HIV/AIDS, rheumatoid arthritis, kidney disease, Crohn's disease and other acute or chronic inflammatory diseases — can interfere with the production of red blood cells.
• Aplastic anemia. This rare, life-threatening anemia occurs when your body doesn't produce enough red blood cells. Causes of aplastic anemia include infections, certain medicines, autoimmune diseases and exposure to toxic chemicals.
• Anemias associated with bone marrow disease. A variety of diseases, such as leukemia and myelofibrosis, can cause anemia by affecting blood production in your bone marrow. The effects of these types of cancer and cancer-like disorders vary from mild to life-threatening.
• Hemolytic anemias. This group of anemias develops when red blood cells are destroyed faster than bone marrow can replace them. Certain blood diseases increase red blood cell destruction. You can inherit a hemolytic anemia, or you can develop it later in life.
• Sickle cell anemia. This inherited and sometimes serious condition is a hemolytic anemia. It's caused by a defective form of hemoglobin that forces red blood cells to assume an abnormal crescent (sickle) shape. These irregular blood cells die prematurely, resulting in a chronic shortage of red blood cells.