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What is Anemia?

Tuesday, May 2, 2023 - 12:56
Contributors to this article: 

Guy Slowik FRCS

Anemia is a condition in which the blood does not supply the body with enough oxygen.  This is because, in anemia, either the number of red blood cells circulating in the body is lower than normal  or the levels of hemoglobin inside the red blood cells fall below normal. 

If hemoglobin and/or red blood cell levels are low, less oxygen is delivered to the tissues by the blood.

As a result, people with anemia often feel tired, weak, cold, and short of breath.

Red blood cells (known as “RBC's" or erythrocytes)  carry oxygen from the lungs to the tissues and remove carbon dioxide and other waste products from the tissues. 

Hemoglobin is the iron-containing red pigment that gives the red blood cells their color; and it also gives red blood cells their ability to carry oxygen.

Anemia is the most common disorder of the red blood cells, affecting about 3.5 million Americans.


hemoglobin, red blood cells and oxygen



Why Does Anemia Occur (What causes anemia)?

There are different causes for anemia.

Anemia occurs if either:

  • The body is not making enough red blood cells (decreased red cell production)
  • The body is destroying too many red blood cells (increased red cell destruction) 
  • The body is losing blood (for example from heavy menstrual periods or internal or external bleeding)
  • The body is lacking the ingredients to produce enough (or healthy) hemoglobin

These different causes of anemia result in many many different types of anemia (different medical conditions).

Thus, anemia is not a disease. Like a fever, anemia indicates that another problem is occurring in the body.

The types of anemia caused by decreases in red cell production include iron deficiency anemia and vitamin deficient anemia.

The type of anemia caused by the body destroying to many red blood cells (and the the bone marrow can't catch up production of new red blood cells)  is often inherited. The resulting anemia is called hemolytic anemia.

A severe bleeding episode can result in temporary anemia until the body has had time to make up the blood that was lost. But even small, persistent losses of blood may cause anemia if you eat a poor diet. A healthy person whose diet contains plenty of iron and vitamins can produce large amounts of new blood, reducing the risk of anemia.

Iron deficiency is the most common cause of anemia.

A poor diet can cause anemia.

Anemia may result from various health conditions, medications, or treatments such as chemotherapy.

The more severe types of anemia are often inherited.

Women of childbearing age are twice as likely as their male counterparts to have anemia, mostly because women lose iron through menstruation each month. Iron deficiency anemia affects about nine percent of women in the United States,  according to data from the National Center for Health Statistics. Anemia is far more common in resource-poor countries. The World Health Organization (WHO) estimates that two billion people – 30 percent of the world’s population – are anemic. Iron deficiency anemia affects half of women and 40 percent of children in developing countries. Poor diet and infectious diseases are the major causes of anemia in resource-poor countries.


Facts About Anemia

  • The word anemia is Greek for "without blood."
  • Anemia is a common problem for menstruating women because their iron supplies are depleted monthly.
  • In young children, marrow in all the bones produces red blood cells. As a person ages, red blood cells are eventually produced only in the marrow of the spine, ribs, and pelvis.
  • The life span of a red blood cell is between 90 and 120 days.
  • Old red blood cells are removed from the blood by the liver and spleen, and the iron is returned to the bone marrow to make new cells.
  • The word erythrocyte is derived from the Greek words “erythros” (meaning “red”) and “cyte,” meaning “cell.” Erythrocytes, or red blood cells, were first observed with a microscope in the late 1600s.

Risk Factors for Anemia

Most people can easily avoid anemia by eating an adequate diet that includes enough iron-rich foods. But some people are at greater risk of anemia because of circumstances, illness, family history, genetics, or other factors. Because anemia has many causes, many such risk factors for anemia exist. A few of the most common risk factors are described below.

  • Inadequate iron intake. Not eating enough iron-rich foods is the most common cause of anemia. While most of the developed world has more-than-adequate access to iron-rich foods, resource-poor countries
  • Inadequate intake of vitamin B12. Vitamin B12 plays an important role in the production of red blood cells. Vitamin B12 generally is found  only in animal foods including meat, poultry, fish, eggs, and dairy product (tempeh being the one vegetarian exception to this rule). Strict vegetarians, .
  • Inadequate intake of folate (Vitamin B6). The body needs Vitamin B6 to make hemoglobin. In addition, Vitamin B6 helps increase the oxygen-carrying ability of the blood. Vitamin B6 is found in many foods. Chickpeas (garbanzo beans), beef liver, yellowfin tuna, and salmon are exceptionally rich sources of this vitamin. Most breakfast cereals are fortified with the vitamin: One serving of fortified cereal provides 25 percent of the recommended daily allowance.
  • Intestinal problems. People with underlying intestinal disease such as Crohn’s Disease or celiac disease are at greater risk of developing anemia.
  • Chronic conditions. Many chronic health problems may increase the risk of anemia. These include diabetes, kidney problems, heart disease, thyroid disease, liver disease, and many cancers.  Long-term infections can also contribute to anemia.
  • Pregnancy. A pregnant woman needs to take in enough iron for both her developing fetus and herself. Many pregnant women have difficulty consuming enough iron-rich foods because of pregnancy-related nausea, which is one reason physicians recommend all pregnant women take a multivitamin that contains at least
  • Menstruation. Women who menstruate heavily can lose a significant amount of iron during each period. If this iron loss is not offset by diet or supplements, anemia can result.
  • Family history of anemia. Many types of anemia are inherited. Sickle cell anemia is the most well known of the inherited types of anemia; thalassemia is another inherited disorder that can cause inadequate .
  • Medications. Some medications, especially chemotherapy drugs, can cause anemia. Even common over-the-counter medications can contribute to anemia. For instance, nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen or naproxyn may cause gastrointestinal bleeding, which in turn can cause anemia. Overuse of heartburn medications can inhibit absorption of Vitamin B12 and contribute indirectly to anemia.

Understanding a bit more about blood:

To understand why anemia occurs, one must first understand a little about the composition and function of blood. Blood is a mixture of plasma (the fluid part of the blood) and cells. Blood is about 55 percent plasma and 45 percent cells.

The blood contains several types of cells, including erythrocytes (red blood cells), white blood cells (which help fight off infection), and platelets (which play a vital role in helping blood to clot). About 99 percent of all cells in the blood are erythrocytes. A healthy adult has about 5 million red blood cells in every cubic millimeter of blood.

Red blood cells are concave in shape, which gives them a greater surface area than other cells. In turn, the greater surface area increases their ability to carry oxygen from the lungs to cells in the body – and carbon dioxide away from cells to the lungs.

red blood cells


Red blood cells are made through an extraordinarily complex process that takes several days to complete. Every second, the body makes about two million red blood cells. The average life of a red blood cell is 120 days.

The actual process of red blood cell production takes place in the red bone marrow, the spongy tissue inside the bones. Production of red blood cells is stimulated by erythropoietin, a hormone made by the kidneys when low levels of oxygen are present in the blood. Erythropoietin stimulates "master cells," called stem cells, in the bone marrow to differentiate into red blood cells. Once the stem cell "commits" to becoming a red blood cell, it extrudes its nucleus and fills with hemoglobin.

The process of creating and recycling red blood cells is exceptionally complex. Trouble can occur at any point in this process.


National Center for Health Statistics, FastStats. (2011). Anemia or Iron Deficiency. Retrieved from http://www.cdc.gov/nchs/fastats/anemia.htm

National Institutes of Health. Office of Dietary Supplements. (2011). Dietary Supplement Fact Sheet: Vitamin B6. Retrieved from http://ods.od.nih.gov/factsheets/vitaminb6

National Institutes of Health. Office of Dietary Supplements. (2011). Dietary Supplement Fact Sheet: Vitamin B12. Retrieved from http://ods.od.nih.gov/factsheets/VitaminB12-QuickFacts

World Health Organization. Nutrition, Micronutrient Deficiencies, Iron-deficiency Anemia. Retrieved from: http://www.who.int/nutrition/topics/ida/en/index.html


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