|Classification and external resources|
Iron in heme
Iron deficiency (sideropenia or hypoferremia) is one of the most common of the nutritional deficiencies. Iron is present in all cells in the human body, and has several vital functions. Examples include as a carrier of oxygen to the tissues from the lungs in the form of hemoglobin, as a transport medium for electrons within the cells in the form of cytochromes, and as an integral part of enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and death.
The eventual consequence of iron deficiency is iron deficiency anemia where the body's stores of iron have been depleted and the body is unable to maintain levels of haemoglobin in the blood. Children and pre-menopausal women are the groups most prone to the disease.
Total body iron averages approximately 3.8 g in men and 2.3 g in women. In blood plasma, iron is carried tightly bound to the protein transferrin. There are several mechanisms that control human iron metabolism and safeguard against iron deficiency. The main regulatory mechanism is situated in the gastrointestinal tract. When loss of iron is not sufficiently compensated by adequate intake of iron from the diet, a state of iron deficiency develops over time. When this state is uncorrected, it leads to iron deficiency anemia.
- chronic bleeding (haemoglobin contains iron)
- inadequate intake
- substances (in diet or drugs) interfering with iron absorption
- malabsorption syndromes
- inflammation where it is adaptive to limit bacterial growth
- blood donation
Symptoms of iron deficiency can occur even before the condition has progressed to iron deficiency anaemia.
Symptoms of iron deficiency are not unique to iron deficiency (i.e. not pathognomonic). Iron is needed for many enzymes to function normally, so a wide range of symptoms may eventually emerge, either as the secondary result of the anemia, or as other primary results of iron deficiency. Symptoms of iron deficiency include:
- hair loss
- brittle or grooved nails
- Plummer-Vinson syndrome: painful atrophy of the mucous membrane covering the tongue, the pharynx and the esophagus
- impaired immune function
- restless legs syndrome
Likely lab test results in people with iron deficiency 
- Low serum ferritin *see below
- Low serum iron
- High TIBC (total iron binding capacity)
- It is possible that the fecal occult blood test might be positive, if iron deficiency is the result of gastrointestinal bleeding.
As always, laboratory values have to be interpreted with the lab's reference values in mind and considering all aspects of the individual clinical situation.
Serum ferritin can be elevated in inflammatory conditions and so a normal serum ferritin may not always exclude iron deficiency, and the utility is improved by taking a concurrent C reactive protein (CRP).
Continued iron deficiency may progress to anaemia and worsening fatigue. Thrombocytosis, or an elevated platelet count, can also result. A lack of sufficient iron levels in the blood is a reason that some people cannot donate blood.
Before commencing treatment, there should be definitive diagnosis of the underlying cause for iron deficiency. This is particularly the case in older patients, who are most susceptible to colorectal cancer and the gastrointestinal bleeding it often causes. In adults, 60% of patients with iron deficiency anemia may have underlying gastrointestinal disorders leading to chronic blood loss. It is likely that the cause of the iron deficiency will need treatment as well.
Upon diagnosis, the condition can be treated with iron supplements. The choice of supplement will depend upon both the severity of the condition, the required speed of improvement (e.g. if awaiting elective surgery) and the likelihood of treatment being effective (e.g. if has underlying IBD, undergoing dialysis or is having ESA therapy).
Examples of oral iron that are often used are ferrous sulfate, ferrous gluconate, or amino acid chelate tablets. Recent research suggests the replacement dose of iron, at least in the elderly with iron deficiency, may be as little as 15 mg per day of elemental iron.
Food sources of iron 
Mild iron deficiency can be prevented or corrected by eating iron-rich foods and by cooking in an iron skillet. Because iron is a requirement for most plants and animals, a wide range of foods provide iron. Good sources of dietary iron have haem-iron as this is most easily absorbed and is not inhibited by medication or other dietary components. Three examples are red meat, poultry and insects. Non-haeme sources do contain iron, though it has reduced bioavailability. Examples are lentils, beans, leafy vegetables, pistachios, tofu, fortified bread, and fortified breakfast cereals.
Iron from different foods is absorbed and processed differently by the body; for instance, iron in meat (heme iron source) is more easily absorbed than iron in grains and vegetables ("non-heme" iron source), but heme/hemoglobin from red meat has effects which may increase the likelihood of colorectal cancer. Minerals and chemicals in one type of food may also inhibit absorption of iron from another type of food eaten at the same time. For example, oxalates and phytic acid form insoluble complexes which bind iron in the gut before it can be absorbed.
Because iron from plant sources is less easily absorbed than the heme-bound iron of animal sources, vegetarians and vegans should have a somewhat higher total daily iron intake than those who eat meat, fish or poultry. Legumes and dark-green leafy vegetables like broccoli, kale and oriental greens are especially good sources of iron for vegetarians and vegans. However, spinach and Swiss chard contain oxalates which bind iron making it almost entirely unavailable for absorption. Iron from nonheme sources is more readily absorbed if consumed with foods that contain either heme-bound iron or vitamin C. This is due to a hypothesised "meat factor" which enhances iron absorption.
Following are two tables showing the richest foods in heme and non-heme iron. In both tables, foods serving size may differ from the usual 100g quantity for relevancy reasons. Arbitrarily, the guideline is set to 18 mg, which is the USDA Recommended Dietary Allowance for women aged between 19 and 50.
|Food||Serving Size||Iron||% Guideline|
|pork liver||100g||18 mg||100%|
|lamb kidney||100g||12 mg||69%|
|cooked oyster||100g||12 mg||67%|
|lamb liver||100g||10 mg||57%|
|beef liver||100g||6.5 mg||36%|
|beef heart||100g||6.4 mg||35%|
|Food||Serving Size||Iron||% Guideline|
|raw yellow beans||100g||7 mg||39%|
|soybean kernels||250ml||4.7 mg||26%|
|toasted sesame seeds||30g||4.4 mg||25%|
|candied ginger root||30g||3.4 mg||19%|
Iron deficiency can have serious health consequences that diet may not be able to quickly correct, hence an iron supplement is often necessary if the iron deficiency has become symptomatic.
Bioavailability and bacterial infection 
Iron is needed for bacterial growth making its bioavailability an important factor in controlling infection. Blood plasma as a result carries iron tightly bound to transferrin, and only releases it to cells with appropriate cell markers thus preventing its access to bacteria. Between 15 and 20 percent of the protein content in human milk consists of lactoferrin that binds iron. As a comparison, in cow's milk, this is only 2 percent. As a result, breast fed babies have fewer infections. Lactoferrin is also concentrated in tears, saliva and at wounds to bind iron to limit bacterial growth. Egg white contains 12% conalbumin to withhold it from bacteria that get through the egg shell (for this reason prior to antibiotics, egg white was used to treat infections).
To reduce bacterial growth, plasma concentrations of iron are lowered in inflammatory states in the body, such as those caused by fever, and following surgery after open wounds where it acts as a protection against infection. Reflecting this link between iron bioavailability and bacterial growth, the taking of iron supplements can increase the risk of infection. A moderate iron deficiency, in contrast, can provide protection against acute infection. This is due to the release of hepcidin from the liver.
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Further reading 
- Gropper, Sareen S; Smith, Jack L; Groff, James L (2009). "Enhancers and inhibitors of iron absorption". In . Advanced Nutrition and Human Metabolism (5th ed.). Belmont, California: Wadsworth, Cengage Learning. ISBN 978-0-495-11657-8. Retrieved 2 October 2010 Alternative ISBN 0-495-11657-2
- Umbreit, Jay (2005). "Iron Deficiency: A Concise Review". American Journal of Hematology 78 (3): 225–231. doi:10.1002/ajh.20249. Retrieved 2 October 2010
- Hobbs, Christopher (April 1989). "'Iron-Clad' Foods and Herbs". Vegetarian Times: 70–75
- Iron Rich Foods Extensive information on Iron Rich Foods
- Recommendations to Prevent and Control Iron Deficiency in the United States
- Textbook on iron deficiency in various settings IronTherapy.Org
- Iron Deficiency conditions, symptoms, treatments Iron Deficiency Guide