Section 12. Disorders of Nutrition and Metabolism

Chapter 155. Minerals and Electrolytes

Topics: Introduction | Calcium | Copper | Fluoride | Iodine | Iron | Magnesium | Phosphate | Potassium | Selenium | Sodium | Zinc

Iron

Much of the iron in the body occurs in hemoglobin. Hemoglobin is the component of red blood cells that enables them to carry oxygen and deliver it to the body's tissues. Iron is an important component of hemoglobin and muscle cells. Iron is also necessary for the formation of many enzymes in the body.

The body recycles iron: When red blood cells die, the iron in them is returned to the bone marrow to be used again in new red blood cells. A small amount of iron is lost each day, mainly in cells shed from the lining of the intestine. This amount is usually replaced by the 1 to 2 milligrams of iron absorbed from food each day.

Food contains two types of iron: heme iron (found in animal products) and nonheme iron (found in most foods and in iron supplements). Nonheme iron accounts for more than 85% of iron in the average diet. However, less than 20% of nonheme iron that is consumed is absorbed into the body. Nonheme iron is absorbed better when it is consumed with animal protein and with vitamin C. Heme iron is absorbed much better than nonheme iron.

Iron Deficiency

Iron deficiency is the most common mineral deficiency in the world, causing anemia in men, women, and children.

In adults, iron deficiency is most commonly caused by loss of blood. In premenopausal women, monthly menstrual bleeding may cause the deficiency. In men and postmenopausal women, iron deficiency usually indicates bleeding in the digestive tract--for example, from a bleeding ulcer or a polyp in the colon. The deficiency may also result from bleeding in other areas of the body, such as the kidneys.

Iron deficiency may result from an inadequate diet, primarily in infants and small children, who need more iron because they are growing. Adolescent girls who do not eat meat are at risk of developing iron deficiency because they are growing and starting to menstruate. Pregnant women are also at risk of this deficiency, because the growing fetus requires large amounts of iron.

Symptoms

When iron reserves in the body are exhausted, anemia develops (see Section 14, Chapter 172). Anemia causes paleness, weakness, irritability, drowsiness, and fatigue. Concentration and learning ability may be impaired. When severe, anemia may cause headache, ringing in the ears (tinnitus), spots before the eyes, digestive upset, shortness of breath, dizziness, and a rapid heart rate. Occasionally, severe anemia causes chest pain and heart failure. Menstrual periods may stop.

In addition to anemia, iron deficiency may produce such symptoms as pica (a craving for nonfoods such as ice, dirt, or pure starch), spoon nails (a deformity in which the fingernails are thin and concave), and leg cramps at night. Rarely, iron deficiency may cause a thin membrane to grow across part of the esophagus, resulting in difficulty swallowing.

Diagnosis

The diagnosis of iron deficiency is based on symptoms and on blood test results. Results include a low level of hemoglobin (which contains iron), a low hematocrit (the proportion of red blood cells to the total volume of blood), and a low number of red blood cells, which are abnormally small. The amount of iron in transferrin--the protein that carries iron in blood when iron is not inside red blood cells--is determined. If the amount is less than 10%, iron deficiency is likely. Iron deficiency is confirmed if the level of ferritin (a protein that stores iron) in the blood is low. However, inflammation, infection, cancer, or liver damage can result in a normal or high ferritin level even when iron deficiency is present.

Occasionally, a bone marrow examination is needed to make the diagnosis. A sample of bone marrow cells is removed, usually from the hipbone, through a needle and examined under a microscope to determine the iron content.

Treatment

Because the most common cause of iron deficiency in adults is excessive bleeding, doctors first look for a source of bleeding. Drugs, such as oral contraceptives (birth control pills), may be needed to control excessive menstrual bleeding. Surgery may be needed to repair a bleeding ulcer or remove a polyp in the colon. A blood transfusion may be necessary if the anemia is severe.

General treatment includes daily doses of an iron supplement taken by mouth. Normal dietary intake of iron may not be sufficient to replace lost iron (because less than 20% of iron in a typical diet is absorbed into the body). Iron is absorbed best when the supplement is taken on an empty stomach, 30 minutes before meals or 2 hours after meals, particularly if the meals include foods that reduce the absorption of iron (such as vegetable fibers, phytates, bran, coffee, and tea). However, taking iron supplements on an empty stomach can cause indigestion and constipation. So some people must take the supplements with meals. Antacids and calcium supplements can also reduce iron absorption. Consuming vitamin C in juices or taking it as a supplement enhances iron absorption. Eating small amounts of meat, which contains the easily absorbed form of iron (heme iron), enhances the absorption of the poorly absorbed form of iron (nonheme iron). Iron supplements almost always turn stools black--a harmless side effect.

Rarely, iron is given by injection. Injections are necessary for people who cannot tolerate tablets or for a few people who cannot absorb enough iron from the digestive tract.

Correcting iron deficiency anemia usually takes 3 to 6 weeks, even after the bleeding has stopped. After the anemia is corrected, an iron supplement should be taken for 6 months to replenish the body's reserves. Blood tests are usually performed periodically to determine whether the person is receiving enough iron and to check for continued bleeding.

Women who are not menstruating and men should not take iron supplements or multiple vitamins with iron unless specifically instructed to do so by a doctor. Taking such supplements can make diagnosing bleeding from the intestine difficult. Such bleeding may be due to serious disorders including colon cancer.

Because a developing fetus requires iron, iron supplements are recommended for most pregnant women. Most babies, particularly those who are premature or who have a low birth weight, need an iron supplement. It is given as an iron-fortified formula or, to breastfed babies, as a separate liquid supplement.

Iron Excess

Excess iron can accumulate in the body. Causes include many blood transfusions and iron therapy given in excessive amounts or for too long. Another cause is hemochromatosis, a hereditary disorder. Excess iron consumed all at once causes vomiting, diarrhea, and damage to the intestine. Excess iron consumed over a period of time may damage coronary arteries. Treatment often consists of the drug deferoxamine, which binds with iron and carries it out of the body in urine. Treatment of hemachromatosis consists of bloodletting (phlebotomy).

See the sidebar Hemochromatosis: When Iron Accumulates.