The Facts
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 very common, affecting children and women of all ages - especially women who are menstruating. It's estimated that at least one-fifth of all women in North America have iron-poor blood.
Sickle cell anemia is another well-known type of anemia. This condition affects several million people worldwide. People most commonly affected include those of African descent, Middle Eastern descent, Mediterranean descent, and South Asian descent. It affects about 80,000 African-Americans. Every year, 1 in 12 African-American babies are born with a genetic potential to pass sickle cell anemia on to their children. It's estimated that 1 baby out of 400 among African-Americans will have the disease.
Aplastic anemia is a form of anemia where the bone marrow stops producing blood cells. This type of anemia is very serious, but fortunately, it's 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.
Causes
Anemia is not an actual disease - it's a condition that's caused by some other problem. There are 3 basic ways you can develop anemia:
1) Blood loss
The most common cause of anemia in North America is menstruation. Many women are borderline anemic, usually because their diet lacks the proper nutrients to replace their monthly blood loss. Another frequent cause is gastrointestinal (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
- hemophilia
- hemorrhoids
- hookworms
2) Low production of healthy red blood cells
Insufficient iron in the diet is the most common cause of anemia worldwide. 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 still do occur. People likely to have dietary iron-deficiency anemia are infants, pregnant women, and teenagers going through a growth spurt. Slow bleeding can also cause iron-deficiency anemia. Even healthy people lose up to 1 mL 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 red blood cells.
Individual red blood cells only last about 4 months and must be replaced by new ones, which are made in the bone marrow. If the marrow is destroyed or so badly damaged that it can't produce enough RBCs, it's called aplastic anemia. Some medications and radiation therapy can kill marrow, but the most common cause is an autoimmune reaction. That's when cells that normally protect you against disease attack your own tissue instead. In 75% of cases, the cause of the autoimmune reaction isn't known.
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. Very occasionally, pregnancy can cause temporary aplastic anemia.
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 red blood cells as they are needed by the body. Diseased kidneys cannot produce enough of this hormone to keep the body supplied with red blood cells, leading to anemia.
3) Rapid destruction of red blood cells
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, 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 fairly common 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 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 chemotherapy or radiation therapy, which damage the bone marrow where red blood cells 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 red blood cells, decreased red blood cell lifespan, and blood loss related to dialysis.
