Understanding Anemia -- the Basics

What Is Anemia?

Anemia is a condition that develops when your blood lacks enough healthy red blood cells or hemoglobin. Hemoglobin is a main part of red blood cells and binds oxygen. If you have too few or abnormal red blood cells, or your hemoglobin is abnormal or low, the cells in your body will not get enough oxygen. Symptoms of anemia -- like fatigue -- occur because organs aren't getting what they need to function properly.

Anemia is the most common blood condition in the U.S. It affects about 3.5 million Americans. Women, young children, and people with chronic diseases are at increased risk of anemia. Important factors to remember are:

  • Certain forms of anemia are hereditary and infants may be affected from the time of birth.
  • Women in the childbearing years are particularly susceptible to iron-deficiency anemia because of the blood loss from menstruation and the increased blood supply demands during pregnancy.
  • Older adults also may have a greater risk of developing anemia because of poor diet and other medical conditions.

There are many types of anemia. All are very different in their causes and treatments. Iron-deficiency anemia, the most common type, is very treatable with diet changes and iron supplements. Some forms of anemia -- like the mild anemia that develops during pregnancy -- are even considered normal. However, some types of anemia may present lifelong health problems.

What Causes Anemia?

There are more than 400 types of anemia, which are divided into three groups: 

  • Anemia caused by blood loss
  • Anemia caused by decreased or faulty red blood cell production
  • Anemia caused by destruction of red blood cells 

Anemia Caused by Blood Loss 

Red blood cells can be lost through bleeding, which often can occur slowly over a long period of time, and can go undetected. This kind of chronic bleeding commonly results from the following: 

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Anemia Caused by Decreased or Faulty Red Blood Cell Production 

With this type of anemia, the body may produce too few blood cells or the blood cells may not function correctly. In either case, anemia can result. Red blood cells may be faulty or decreased due to abnormal red blood cells or a lack of minerals and vitamins needed for red blood cells to work properly. Conditions associated with these causes of anemia include the following: 

  • Sickle cell anemia
  • Iron-deficiency anemia
  • Vitamin deficiency
  • Bone marrow and stem cell problems
  • Other health conditions 

Sickle cell anemia is an inherited disorder that, in the U.S. affects mainly African-Americans and Hispanic Americans. Red blood cells become crescent-shaped because of a genetic defect. They break down rapidly, so oxygen does not get to the body's organs, causing anemia. The crescent-shaped red blood cells can also get stuck in tiny blood vessels, causing pain

Iron-deficiency anemia occurs because of a lack of the mineral iron in the body. Bone marrow in the center of the bone needs iron to make hemoglobin, the part of the red blood cell that transports oxygen to the body's organs. Without adequate iron, the body cannot produce enough hemoglobin for red blood cells. The result is iron-deficiency anemia. This type of anemia can be caused by: 

  • An iron-poor diet, especially in infants, children, teens, vegans, and vegetarians
  • The metabolic demands of pregnancy and breastfeeding that deplete a woman's iron stores
  • Menstruation
  • Frequent blood donation
  • Endurance training
  • Digestive conditions such as Crohn's disease or surgical removal of part of the stomach or small intestine
  • Certain drugs, foods, and caffeinated drinks 

Vitamin-deficiency anemia may occur when vitamin B12 and folate are deficient. These two vitamins are needed to make red blood cells. Conditions leading to anemia caused by vitamin deficiency include: 

  • Megaloblastic anemia: Vitamin B12 or folate or both are deficient
  • Pernicious anemia: Poor vitamin B12 absorption caused by conditions such as Crohn's disease, an intestinal parasite infection, surgical removal of part of the stomach or intestine, or infection with HIV
  • Dietary deficiency: Eating little or no meat may cause a lack of vitamin B12, while overcooking or eating too few vegetables may cause a folate deficiency.
  • Other causes of vitamin deficiency: pregnancy, certain medicationsalcohol abuse, intestinal diseases such as tropical sprue and celiac disease 

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During early pregnancy, sufficient folic acid can help prevent the fetus from developing neural tube defects such as spina bifida

Bone marrow and stem cell problems may prevent the body from producing enough red blood cells. Some of the stem cells found in bone marrow develop into red blood cells. If stem cells are too few, defective, or replaced by other cells such as metastatic cancer cells, anemia may result. Anemia resulting from bone marrow or stem cell problems include: 

  • Aplastic anemia occurs when there's a marked reduction in the number of stem cells or absence of these cells. Aplastic anemia can be inherited, can occur without apparent cause, or can occur when the bone marrow is injured by medications, radiationchemotherapy, or infection.
  • Thalassemia occurs when the red cells can't mature and grow properly. Thalassemia is an inherited condition that typically affects people of Mediterranean, African, Middle Eastern, and Southeast Asian descent. This condition can range in severity from mild to life-threatening; the most severe form is called Cooley's anemia.
  • Lead exposure is toxic to the bone marrow, leading to fewer red blood cells. Lead poisoning occurs in adults from work-related exposure and in children who eat paint chips, for example. Improperly glazed pottery can also taint food and liquids with lead. 

Anemia associated with other conditions usually occurs when there are too few hormones necessary for red blood cell production. Conditions causing this type of anemia include the following: 

Anemia Caused by Destruction of Red Blood Cells 

When red blood cells are fragile and cannot withstand the routine stress of the circulatory system, they may rupture prematurely, causing hemolytic anemia. Hemolytic anemia can be present at birth or develop later. Sometimes there is no known cause. Known causes of hemolytic anemia may include: 

  • Inherited conditions, such as sickle cell anemia and thalassemia
  • Stressors such as infections, drugs, snake or spider venom, or certain foods
  • Toxins from advanced liver or kidney disease
  • Inappropriate attack by the immune system (called hemolytic disease of the newborn when it occurs in the fetus of a pregnant woman)
  • Vascular grafts, prosthetic heart valves, tumors, severe burns, exposure to certain chemicals, severe hypertension, and clotting disorders
  • In rare cases, an enlarged spleen can trap red blood cells and destroy them before their circulating time is up.
WebMD Medical Reference Reviewed by Laura J. Martin, MD on June 26, 2016

Sources

SOURCES:
American Academy of Family Physicians.
The American Medical Athletic Association.
Albemarle Pulmonary Medical Associates, PA.
Gary W. Tamkin, MD, Attending Physician, Highland General Hospital -- Alameda County Medical Center, Oakland.
Cornell University Department of Animal Science.

CDC.

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