Human iron metabolism is the set of chemical reactions maintaining human homeostasis of iron. The control of this necessary but potentially toxic substance is an important part of many aspects of human health and disease. Hematologists have been especially interested in the system of iron metabolism because iron is essential for red blood cells, where most of the human body's iron is contained. Understanding this system is also important for understanding diseases of iron overload, like hemochromatosis, and iron deficiency, like iron deficiency anemia.
Iron is an absolute requirement for most forms of life, including humans and most bacterial species. Plants and animals all use iron; hence, iron can be found in a wide variety of food sources.
Iron is essential to life due to its unusual flexibility to serve as both an electron donor and acceptor.
Iron can also be potentially toxic. Its ability to donate and accept electrons means that if iron is free within the cell, it can catalyze the conversion of hydrogen peroxide into free radicals. Free radicals can cause damage to a wide variety of cellular structures, and ultimately kill the cell. To prevent that kind of damage, all life forms that use iron bind the iron atoms to proteins. This binding allows cells to benefit from iron while also limiting its ability to do harm.
The most important group of iron-binding proteins contain the heme molecules, all of which contain iron at their centers. Humans and most bacteria use variants of to carry out redox reactions and electron transport processes. These reactions and processes are required for oxidative phosphorylation. That process is the principal source of energy for human cells; without it, most types of cells would die.
The iron-sulfur proteins are another important group of iron-containing proteins. Some of these proteins are also essential parts of oxidative phosphorylation.
Humans also use iron in the hemoglobin of red blood cells, in order to transport oxygen from the lungs to the tissues. Iron is also an essential component of myoglobin to store and diffuse oxygen in muscle cells.
The human body needs iron for oxygen transport. That oxygen is required for the production and survival of almost all cells in our bodies (mature erythrocytes being one exception). Human bodies tightly regulate iron absorption and recycling. Iron is such an essential element of human life, in fact, that humans have no physiologic regulatory mechanism for excreting iron. Most humans prevent iron overload solely by regulating iron absorption. Those who cannot regulate absorption well enough get disorders of iron overload. In these diseases, the toxicity of iron starts overwhelming the body's ability to bind and store it.
Iron is a mineral found in every cell of the body. Iron is considered an essential mineral because it is needed to make part of blood cells.
The human body needs iron to make the oxygen-carrying proteins hemoglobin and myoglobin. Hemoglobin is found in red blood cells and myoglobin is found in muscles.Iron also makes up part of many proteins in the body.
Food Sources
The best sources of iron include:
Dried beans, dried fruits, eggs (especially egg yolks), iron-fortified cereals, liver, lean red meat (especially beef), oysters, poultry, dark red meat, salmon, tuna, whole grains.
Reasonable amounts of iron are also found in lamb, pork, and shellfish.
Iron from vegetables, fruits, grains, and supplements is harder for the body to absorb. These sources include:Dried fruits, prunes, raisins, apricots, legumes, lima beans, soybeans, dried beans and peaskidney beans, seeds, almonds, brazil nuts, vegetables, broccoli, spinach, kale, collardsasparagus, dandelion greens, Whole grains, wheat, millet, oatsbrown rice.
If you mix some lean meat, fish, or poultry with beans or dark leafy greens at a meal, you can improve absorption of vegetable sources of iron up to three times. Foods rich in vitamin C also increase iron absorption.
Some foods reduce iron absorption. For example, commercial black or pekoe teas contain substances that bind to iron so it cannot be used by the body.
Side Effects
Low Iron Levels
The human body stores some iron to replace any that is lost. However, low iron levels over a long period of time can lead to iron deficiency anemia. Symptoms include lack of energy, shortness of breath, headache, irritability, dizziness, or weight loss. For more details on this condition see iron deficiency anemia.
Those at risk for low iron levels include:Women who are menstruating, especially if they have heavy periodsWomen who are pregnant or who have just had a babyLong-distance runnersPeople with any type of bleeding in the intestines (for example, a bleeding ulcer)People who frequently donate bloodPeople with gastrointestinal conditions that make it hard to absorb nutrients from foodBabies and young children are at risk for low iron levels if they do not receive the appropriate foods. Babies moving to solid foods should eat iron-rich foods. Infants are born with enough iron to last about six months. An infant's additional iron needs are met by breast milk. Infants that are not breastfed should be given an iron supplement or iron-fortified infant formula.Children between age 1 and 4 grow rapidly, which uses up iron in the body. They should be given iron-fortified foods or iron supplements. Note: Milk is a very poor source of iron. Children who drink large quantities of milk and avoid other foods may develop "milk anemia." Recommended milk intake is two to three cups per day for toddlers.Adolescents are more prone to low iron levels because of rapid growth rates and inconsistent eating habits.
Too Much Iron
The genetic disorder called hemochromatosis affects the body's ability to control how much iron is absorbed. This leads to too much iron in the body. Treatment consists of a low-iron diet, no iron supplements, and phlebotomy (blood removal) on a regular basis.
It is unlikely that a person would take too much iron. However, children can sometimes develop iron poisoning by swallowing too many iron supplements. Symptoms of iron poisoning include:Fatigue, anorexia, dizziness, nausea, vomiting, headache, weight loss, shortness of breathgrayish color to the skin.
