Anemia is a condition where the number of healthy red blood cells (RBCs) in the blood is lower than normal. RBCs transport oxygen throughout the body, so a shortage of these cells can be serious.
Iron-deficiency anemia is the most common type of anemia. It commonly affects children and women of all ages - especially women who are menstruating. It's estimated that at least 1 in 5 women in North America does not have enough iron in her blood. It can also seriously affect men when it is caused by colon polyps, colon cancer, or other gastrointestinal (GI) malignancies (cancers). Iron-deficiency anemia is often one of the first warning signals that a person may have a GI malignancy.
Sickle-cell anemia is another well-known type of anemia. This condition affects millions of people worldwide. It is a hereditary disease, passed on to children by parents with the altered genetic material. People most commonly affected include those of African descent, Middle Eastern descent, Mediterranean descent, and East Indian descent. Every year, 1 in 12 African American babies is born with a genetic potential to pass sickle-cell anemia on to their children. It's estimated that 1 out of 400 African American babies will have the disease.
Aplastic anemia is a form of anemia where the bone marrow stops producing all types of blood cells. This type of anemia is very serious, but fortunately rare. It affects 2 to 12 out of every million people each year. Aplastic anemia occurs in both adults and children.
Anemia of chronic disease is a mild form of anemia that occurs with people who have diseases that last more than 1 to 2 months. Such diseases include tuberculosis, HIV, cancer, kidney disease, rheumatologic disorders, and liver disease.
Pernicious anemia is a form of anemia more common in elderly people and is caused by either a lack of dietary intake or poor absorption of vitamin B12 from the diet. It is also a common condition seen in alcoholics.
Anemia is not an actual disease - it's a condition that's caused by some other problem. There are three basic ways you can develop anemia:
The most common cause of anemia in North America is blood loss. Many women are borderline anemic, usually because their diets lack the proper nutrients to replace their monthly blood loss through menstrual flow. Another frequent cause is GI bleeding due to illnesses like ulcerative colitis, diverticulitis, and colon cancer. Use of certain medications such as aspirin* and nonsteroidal anti-inflammatory drugs (NSAIDs) may also cause GI bleeding.
Other conditions that can cause bleeding include:
- gastric ulcers
Low production of healthy RBCs
The body needs iron to make hemoglobin, a protein in RBCs that carries the oxygen from the lungs to the rest of the body. Hemoglobin also gives blood its red color. In addition to lack of iron, there can be a lack of vitamin B12 and folic acid in the diet as well.
These deficiencies are less common in North America, but they still occur. People with increased iron requirements include infants, pregnant women, and teenagers going through a growth spurt. Slow bleeding can also cause iron-deficiency anemia. Even healthy people lose a small amount of blood in their stool. A slightly larger amount can easily go unnoticed and yet be enough to cause anemia.
The cause of anemia of chronic disease is not completely understood. It is related to a decreased production of RBCs.
Individual RBCs only last about 4 months and must be replaced by new ones, which are made in the bone marrow. Aplastic anemia is caused when the marrow is destroyed or so badly damaged that it can't produce enough RBCs. Some medications and radiation therapy can kill bone marrow, but the most common cause is an autoimmune reaction. This occurs when cells that normally protect you against disease attack your own tissue instead. In 50% of cases, the cause of the autoimmune reaction is unknown.
Other conditions that can destroy bone marrow and cause aplastic anemia include viral hepatitis and severe rheumatoid arthritis. Fanconi's anemia is a rare inherited aplastic condition in which the bone marrow is deficient. Anemia is common for people who have severe kidney disease. This is because healthy kidneys make a hormone called erythropoietin, a natural hormone that causes the bone marrow to produce more RBCs as they are needed by the body. Diseased kidneys cannot produce enough of this hormone to keep the body supplied with RBCs, leading to anemia.
Rapid destruction of RBCs
Healthy bone marrow can only produce so many RBCs a month. If the body is destroying cells faster than they are made, anemia will result. Old, "worn out" RBCs are mostly broken down in the spleen, which is the organ that filters the blood, checks it for infection, and removes undesirable substances. Some conditions can cause the spleen to grow larger. A variety of conditions may cause hypersplenism (enlarged spleen), including liver disease, malaria, lupus, or tuberculosis. An oversized spleen can trap and destroy even healthy RBCs, causing anemia
Sickle cell anemia and thalassemia are inherited diseases in which the RBCs are deformed. Sickle cell anemia is widespread among people of African American descent, while thalassemia tends to run in families of Mediterranean descent. Sickle cell anemia is a genetic disease that occurs when individuals receive a copy of the sickle cell gene from both parents, resulting in misshapen or crescent-shaped RBCs. The spleen recognizes them as abnormal, and it grows to cope with the extra workload of destroying them. This destruction of RBCs causes anemia. Interestingly, the gene that causes sickle cell disease also gives people protection from a parasite that causes malaria.
Anemia can also be caused by a combination of factors. Anemia is very common in people with cancer. In fact, about half of people with cancer develop anemia. It can have a variety of different causes, including chemotherapy or radiation therapy that damage the bone marrow where RBCs are produced, tumors in the bone marrow, blood loss, poor nutrition, or a combination of these reasons.
In people with severe kidney disease, anemia is caused by a combination of decreased production of RBCs, decreased RBC lifespan, and blood loss related to dialysis.