Anemia has several causes. In general, anemia occurs when the number of RBCs or the amount of hemoglobin in them is below normal. This can occur if the body fails to produce enough RBCs, destroys them faster than they can be replaced, or loses too many of them through bleeding. The symptoms of anemia occur because people who are anemic cannot transport enough oxygen in their blood to feed all their body tissues. As a result, they feel fatigued and their heart has to work harder to pump the blood through the body more often. Common types of anemia and their causes include:

• Iron-deficiency anemia: As the name suggests, this type of anemia is caused by a lack of iron. Iron is a vital part of the hemoglobin molecule; without an adequate amount of iron, your body cannot make enough hemoglobin. The human body is very efficient at recycling iron and so the dietary need for iron is low for most people. However, if blood is lost, even small amounts, and not replaced, you can become iron deficient. This may occur in as many as one in every five reproductive-age women, although estimates of its prevalence vary widely. It also affects nearly half of pregnant women.  Slow, chronic bleeding within the body, such as a stomach ulcer, or inflammatory bowel disease, or even excessive use of drugs such as aspirin or ibuprofen can also lead to iron loss and iron deficiency anemia.


• Vitamin deficiency anemias: In addition to iron, there are several vitamins that are required to produce healthy RBCs. These include folate, vitamin B6 and vitamin B12. Lack of any of these in your diet can lead to decreased RBC production and thus anemia. Pernicious anemia is a relatively rare type of anemia caused by vitamin B12 deficiency. People with pernicious anemia lack an important molecule called intrinsic factor that helps people absorb B12 from their diet, so no matter how much B12 they eat they cannot get enough to make healthy RBCs. Pernicious anemia mostly occurs in adults over 60 and is more common in people of Scandinavian and Northern European decent.


• Anemia caused by chronic disease: Several chronic diseases can also cause anemia including rheumatoid arthritis, cancer, and kidney failure among others. Long-term inflammation and low levels of a hormone called erythropoietin that are caused by these diseases or their treatments can interfere with RBC production and cause anemia.


• Aplastic anemia: Red blood cells are normally produced in the bone marrow. Sometimes, the bone marrow stops producing RBCs at normal levels, often for unknown reasons. Some identifiable factors that can be responsible for aplastic anemia include chemotherapy, radiation therapy, environmental toxins, pregnancy, and autoimmune disorders such as lupus.


• Leukemia: Cancer of the blood-forming cells of the bone marrow, also called leukemia, can dramatically change the production of RBCs and other blood cells, leading to anemia. Other cancers that affect the blood, such as multiple myeloma and lymphoma can also cause anemia.


• Hemolytic anemia: When blood cells are destroyed faster than they can be replaced, anemia results. The normal lifespan for an RBC in the bloodstream is around 120 days. Certain blood disorders, autoimmune diseases, or medications can shorten this lifespan considerably, in some cases to 10 days or less. This leads to anemia and may also cause skin yellowing called jaundice as the broken down blood by-products build up in the body faster than they can be eliminated.


• Sickle cell anemia: This is an inherited genetic condition that mainly affects people of African and Arabic descent. When a person inherits two copies of the gene that causes the disease, their hemoglobin molecules are defective. The name of the disease comes from the tendency of RBCs containing this defective hemoglobin to shrivel up and form a sickle or crescent shape, making it impossible for them to carry oxygen. These cells last only a brief period in the bloodstream before they are removed, but because of their odd, often pointed, shapes they can also get stuck in the small blood vessels in the body, producing painful symptoms.


• Other anemias: Several other types of anemia exist, such as the alpha- and beta-thalassemias which are caused by defective hemoglobin production. Caused by a genetic mutation, thalassemias lead to anemia by decreasing the production of hemoglobin and reducing the oxygen carrying capacity of the RBCs. Thalassemias are more common in people of Italian and Mediterranean or Middle Eastern descent.