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 gastrointestinal (GI) bleeding due to illnesses like ulcerative colitis, diverticulitis, and colon cancer. Use of certain medications such as acetylsalicylic acid* (ASA) 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 on RBCs that carries the oxygen from the lungs to the rest of the body. Hemoglobin also gives blood its red colour. In addition to lack of iron, there tends to 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 a day 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. If your marrow is destroyed or so badly damaged that it can't produce enough RBCs, you have aplastic anemia. 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 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 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 killing them. This destruction of RBCs causes anemia. Interestingly, the gene that causes sickle cell disease also gives people resistance to, or 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 tumours in the bone marrow, blood loss, poor nutrition, chemotherapy or radiation therapy that damages the bone marrow where RBCs are produced, 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.