What Causes Iron-Deficiency Anemia?

Iron-deficiency anemia occurs when there is too little iron in the body. A person can have a low iron level for three reasons:

• Blood loss, either from disease or injury
• Not getting enough iron in the diet
• Not being able to absorb the iron in the diet

Iron-deficiency anemia also can develop when the body needs higher levels of iron, such as during pregnancy.

Loss of Iron Through Blood Loss

In general, when blood is lost, iron is lost. If the body does not have enough iron reserves to make up for the iron loss, a person will develop iron-deficiency anemia.

Blood is lost in a number of ways. In women, iron and red blood cells are lost when bleeding occurs from very long or heavy menstrual periods as well as from childbirth. Women also can lose iron and red blood cells from slowly bleeding fibroids in the uterus.

Blood also is lost through internal bleeding. Most often this loss of blood occurs slowly and can be due to:

• A bleeding ulcer, colon polyp, or colon cancer
• Regular use of aspirin or other pain medicine such as nonsteroidal anti-inflammatory drugs (for example, ibuprofen and naproxen)
• Hookworm infection
• Urinary tract bleeding

A more rapid loss or removal of blood that can cause iron-deficiency anemia occurs in situations such as:

• Severe injuries
• Surgery
• Frequent blood drawing

Lack of Iron in the Diet

Meat, poultry, fish, eggs, dairy products, or iron-fortified foods (that is, foods that have iron added) are the best sources of iron found in food. Eating patterns that exclude these foods or food supplements may lead to iron-deficiency anemia. For example, some vegetarians do not eat enough foods with iron. Other people get iron-deficiency anemia because of eating poorly due to alcoholism or aging. Following a diet that has an imbalance of food groups also can lead to this type of anemia. Examples of diets that can lead to iron-deficiency anemia include:

• Low-fat diets. Following a low-fat diet over a long period of time may limit sources of iron from animal foods.
• Diets high in sugars. These types of diets are often low in iron.
• High-fiber diets. These types of diets can slow the absorption of iron.

Infants who are fed cow's milk in the first year are at risk for iron-deficiency anemia because cow's milk is low in iron. The same is true for infants who are breastfed after 4 months of age. These infants need iron supplements.

An Increased Need for Iron

People may need more iron at some periods in their lives. If they do not get more iron at these times, they may develop iron-deficiency anemia. Periods of rapid growth or growth spurts in children and teens are a good example of an increased need for iron. Pregnancy also is an example. The need for iron doubles during pregnancy due to an increased blood volume, the growth of the fetus, and the blood loss that occurs during childbirth.

Inability To Absorb Enough Iron From Food

Certain factors make it hard for the body to absorb enough iron from food. These factors include:

• Intestinal surgery or diseases of the intestine, such as Crohn's disease or celiac disease
• Prescription medicines that reduce acid in the stomach
• Low levels of folate, vitamin B12, or vitamin C in the diet

How Iron-Deficiency Anemia Develops

First, iron is lost from the body by one of the ways listed above. Usually, this happens slowly over a period of time. Most often, the person is not taking in enough iron to meet the needs of the body.

Next, the body starts to use iron that it has stored. When the stored iron is used up, new red blood cells have less hemoglobin than normal, and fewer red blood cells are produced. Finally, when the number of red cells is too low, iron-deficiency anemia develops.