Iron deficiency, or sideropenia, is the state in which a body lacks enough iron to supply its needs. Iron is present in all cells in the human body and has several vital functions, such as carrying oxygen to the tissues from the lungs as a key component of the hemoglobin protein, acting as a transport medium for electrons within the cells in the form of cytochromes, and facilitating oxygen enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and death. ^[1]

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 iron metabolism and safeguard against iron deficiency. The main regulatory mechanism is situated in the gastrointestinal tract. The majority of iron absorption occurs in the small intestine called duodenum. A number of dietary factors may affect iron absorption. When loss of iron is not sufficiently compensated by 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, a common type of anemia. ^[1]Before

anemia occurs, the medical condition of iron deficiency without anemia is called latent iron deficiency (LID).
Anemia is a condition characterized by inadequate red blood cells (erythrocytes) or hemoglobin. When the body lacks sufficient amounts of iron, production of the protein hemoglobin is reduced. Hemoglobin binds to oxygen, enabling red blood cells to supply oxygenated blood throughout the body. Women of child-bearing age, ^[2]children, and people with poor diet are most susceptible to the disease. Most cases of iron-deficiency anemia are mild, but if not treated can cause problems like an irregular heartbeat, pregnancy complications, and delayed growth in infants and children that could affect their cognitive development and their behavior. ^[3]

Signs and symptoms

Symptoms of iron deficiency can occur even before the condition has progressed to iron deficiency anemia.
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:

· fatigue

· dizziness/lightheadedness

· pallor

· hair loss

· twitches

· irritability

· weakness

· pica

· brittle or grooved nails

· hair thinning

· Plummer–Vinson syndrome: painful atrophy of the mucous membrane covering the tongue, the pharynx and the esophagus

· impaired immune function ^[4]

· pagophagia

· restless legs syndrome ^[5]

Continued iron deficiency may progress to anemia 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.

Signs and symptoms in children

· pale skin

· fatigue

· slowed growth and development

· poor appetite

· behavioral problems

· abnormal rapid breathing

· frequent infection

Treatment

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. ^[6]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 the patient has underlying IBD, is 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. ^[7]

Food sources

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 heme-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. ^{[8] [9]} Non-heme 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 sources). ^[10]Minerals and chemicals in one type of food may also inhibit absorption of iron from another type of food eaten at the same time. ^[11] 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. ^[12]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.[citation needed] Iron from non-heme 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. ^[13]

Following are two tables showing the richest foods in heme and non-heme iron. ^[14] In both tables, food serving sizes may differ from the usual 100g quantity for relevancy reasons. Arbitrarily, the guideline is set at 18 mg, which is the USDA Recommended Dietary Allowance for women aged between 19 and 50. ^[15]

Abstract: richest foods in heme iron
Food	Serving size	Iron	% guideline
clam[a]	100g	28 mg	155%
pork liver	100g	18 mg	100%
lamb kidney	100g	12 mg	69%
cooked oyster	100g	12 mg	67%
cuttlefish	100g	11 mg	60%
lamb liver	100g	10 mg	57%
octopus	100g	9.5 mg	53%
mussel	100g	6.7 mg	37%
beef liver	100g	6.5 mg	36%
beef heart	100g	6.4 mg	35%

Abstract: richest foods in non-heme iron
Food	Serving size	Iron	% guideline
raw yellow beans	100g	7 mg	35%
spirulina	15g	4.3 mg	24%
falafel	140g	4.8 mg	24%
soybean kernels	125ml=1/2cup	4.6 mg	23%
spinach	125g	4.4 mg	22%
lentil	125ml=1/2cup	3.5 mg	17.5%
treacle (CSR Australia)	20ml=1Tbsp	3.4 mg	17%
molasses (Bluelabel Australia)	20ml=1Tbsp	1.8 mg	9%
candied ginger root	15g~3p	1.7 mg	8.5%
toasted sesame seeds	10g	1.4 mg	7%
cocoa (dry powder)	5g~1Tbsp	.8 mg	4%

Food recommendations for children

Children at 6 months should start having solid food that contains enough iron, which could be found in both heme and non-heme iron ^[16]

Heme iron :

· Red meat (for example, beef, pork, lamb, goat, or venison)

· Fatty fish

· Poultry (for example, chicken or turkey)

· Eggs

Non-heme iron :
· Iron-fortified infant cereals
· Tofu
· Beans and lentils
· Dark green leafy vegetables

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.

Food recommendations for Infant

Add egg yolk, fish paste, poultry blood, etc. for 4 to 5 months; add liver paste, minced meat, blood, red date paste and other foods from 7 months; in addition, for premature infants from 2 months, and full-term infants from 4 Iron can be supplemented under guidance from the first month to strengthen prevention. On April 29, 2014, the National Health and Planning Commission of the People's Republic of China issued a national food safety standard for complementary food supplements for infants and young children aged 6-36 months and children aged 37-60 months.

References

1. Centers for Disease Control and Prevention (3 April 1998). "Recommendations to Prevent and Control Iron Deficiency in the United States". Morbidity and Mortality Weekly Report. Recommendations and Reports. 47 (RR-3): 1–36. PMID 9563847.
2.  "Women of reproductive age (15-49 years) population (thousands)". www.who.int.
3.  "Iron and Iron Deficiency". Centers for Disease Control and Prevention. 23 February 2011. Archived from the original on 8 September 2014. Retrieved 12 August 2014.
4. Wintergerst, E. S.; Maggini, S.; Hornig, D. H. (2007). "Contribution of Selected Vitamins and Trace Elements to Immune Function" (PDF). Annals of Nutrition and Metabolism. 51 (4): 301–323. doi:10.1159/000107673. PMID 17726308.
5.  Rangarajan, Sunad; D'Souza, George Albert. (April 2007). "Restless legs syndrome in Indian patients having iron deficiency anemia in a tertiary care hospital". Sleep Medicine. 8 (3): 247–51. doi:10.1016/j.sleep.2006.10.004. PMID 17368978.
6. Rockey D, Cello J (1993). "Evaluation of the gastrointestinal tract in patients with iron-deficiency anemia". N Engl J Med. 329 (23): 1691–5. doi:10.1056/NEJM199312023292303. PMID 8179652.
7.  Rimon E, Kagansky N, Kagansky M, Mechnick L, Mashiah T, Namir M, Levy S (2005). "Are we giving too much iron? Low-dose iron therapy is effective in octogenarians". Am J Med. 118 (10): 1142–7. doi:10.1016/j.amjmed.2005.01.065. PMID 16194646.
8.  Defoliart G (1992). "Insects as Human Food". Crop Protection. 11 (5): 395–99. doi:10.1016/0261-2194(92)90020-6.
9.  Bukkens SGF (1997). "The Nutritional Value of Edible Insects". Ecol. Food. Nutr. 36 (2–4): 287–319. doi:10.1080/03670244.1997.9991521.
10.  Iron deficiency Archived 8 August 2006 at the Wayback Machine Food Standards Agency.
11.  Iron in diet. MedlinePlus.
12.  Mangels, Reed. Iron in the vegan diet. The Vegetarian Resource Group.
13.  Iron. The Merck Manuals Online Medical Library.
14. Iron rich foods Archived 18 May 2017 at the Wayback Machine. Rich Foods.
15. Dietary Reference Intakes: Recommended Intakes for Individuals Archived 6 September 2013 at the Wayback Machine National Academy of Sciences. Institute of Medicine. Food and Nutrition Board.
16.  CDC (3 December 2018). "Iron - Infant and Toddler Nutrition". Centers for Disease Control and Prevention. Retrieved 26 April 2019.