Anemia is a lack of red blood cells and/or the iron-rich molecule in red blood cells (hemoglobin) that carries oxygen throughout the body and gives blood its red color. If the body does not have enough oxygen, the muscles and organs cannot function properly, which can lead to fatigue and other symptoms of anemia.

Anemia may be caused when the bone marrow, which produces new red blood cells to replace the normal, daily destruction of old ones, cannot produce enough new red blood cells to keep up with the body's demand. It may also occur when the red blood cells are abnormally short-lived. Alternatively, it may be caused by a lack of available hemoglobin on the existing red blood cells.

Red blood cells are produced in the bone marrow, which is the soft, inner part of the bones. Besides red blood cells, the bone marrow produces white blood cells, which are part of the immune system, and platelets, which help repair damaged blood vessels.

The average normal blood hemoglobin level for adults for men is 14 to 17 grams/deciliter (g/dL) and 12 to 15 g/dL for women. Anemia may be defined as a blood hemoglobin level under 12 grams/deciliter. However, many individuals do not experience symptoms of anemia until their hemoglobin level drops below 10 g/dL especially if the decline has been gradual over weeks to months.

Anemia is not always a primary disease but can be a sign of another disease process. It can be either chronic (developing over a long period of time) or acute (rapid onset). While anemia can be linked to more than 100 causes, the three basic reasons for the condition are:

• The body is losing red blood cells (bleeding)
• The body is not producing enough red blood cells
• The body’s red blood cells are being destroyed (e.g. antibodies, chemicals)

Anemia is a common condition, particularly among:

• Pregnant women
• Women who have a heavy menstrual flow
• Infants
• Older adults with poor nutrition
• African Americans
• Alaskan natives
• Native Americans
• Immigrants from developing countries
• Individuals of lower socioeconomic status