Iron EME and Iron non-EME
The human body contains about 3-4 g of iron.
Based on the link with hemoglobin and the oxidation state, two different types of iron can be distinguished:
- heme iron (or emic iron ): it is the iron bound to hemoglobin or myoglobin, in which it is in the oxidation state Fe2 + ( ferrous ion ); only in this oxidation state can iron bind oxygen;
- non-heme iron (or non-heme iron ): it is iron bound to deposit proteins (such as ferritin), in which it is in the oxidation state Fe3 + ( ferric ion ).
Hemic iron amounts to about 75% of the total iron present in the body (65% in hemoglobin and 10% in myoglobin).
In small quantities (0.1-0.5% of the total) this element is found in some intracellular enzymes and in transferrin, a glycoprotein that gives it to the bone marrow hemoglobin. In this way the non-emic iron is converted into emic iron.
Functions and requirements
Iron is necessary for the synthesis of hemoglobin (protein that carries oxygen to cells), myoglobin and collagen; it is also indispensable in the processes of cellular respiration and in the metabolism of nucleic acids.
According to the tables of the LARN (Recommended Daily Intake Levels of Nutrients for the Italian Population) the daily requirement of iron for humans amounts to 10mg, while for women of childbearing age it rises to 18mg. Normally an adequate diet compensates for the elimination of iron and the balance is kept in balance, thanks to the reserves and the regulation of absorption and elimination.
Iron in Food
Foods rich in iron are: meat, liver, legumes, shellfish, dried fruit and green vegetables. Instead, they contain minimal amounts of iron: butter, milk and alcohol (with the exception of wine).
The iron present in the food is absorbed slowly and to a limited extent (from 5 to 10% of the ingested iron). The absorption depends above all on the form in which it is found in the food:
- the emic iron is better absorbed than the non-emic one . Hemic iron is present only in meat, being a residue of the muscular myoglobin of the animal;
- non-emic iron is found in all foods (including meat) and is divided into:
- ferrous iron Fe2 +, among the two best absorbed, is typical of foods of animal origin;
- ferric iron Fe3 +, is typical of vegetables.
In vegetables, iron is present in the Fe3 + form, more precisely in the form of iron hydroxide, or in a highly liable way linked to organic compounds such as citrates, lactates and sugars. Furthermore, in vegetables, antinutritional factors are often present, such as phytates and oxalates, which limit intestinal absorption.
Non-EME iron Fe3 + will only be absorbed after being released and reduced to Fe2 +.
Reducing substances, such as ascorbic acid (vitamin C), citric acid and -SH groups (sulphidryl), and substances that keep it soluble such as fructose (sugar present in fruit), help iron absorption favoring the reduction from Fe3 + to Fe2 +. For this reason, it is advisable to use anemic sources of iron in combination with citrus fruits or vitamin C supplements.
The absorption of iron is inhibited by hypochloridria (decrease in the concentration of hydrochloric acid in the stomach) and increased gastric pH (typical iron-free anemia of the elderly with hypo or achlorhydria) and by the presence of phytates, oxalates, phosphates contained in vegetables, which form insoluble coffee and tea complexes with iron.
Deepening: Diet to Maximize Iron Absorption
Easily absorbable iron
FOOD | Mg of iron / 100 grams | Mg of iron presumably absorbed per 100 grams of food |
Liver, offal, seafood | 5-10 | 0.77 |
Horse meat | 3.9 | 0.9 |
Beef | 2.5 | 0.6 |
Other meats (including cold cuts) | 1-2 | 0.3-0.4 |
Pisces | 1 | 0.1 |
Iron difficult to absorb
FOOD | Mg of iron / 100 grams | Mg of iron presumably absorbed per 100 grams of food |
Cocoa, yeast | 10 | 0.5 |
VEGETABLES (radicchio, spinach, endive, broccoli) DRIED OILY FRUIT (walnuts, hazelnuts) CHOCOLATE | 1 - 5 | 0.2 |
LEGUMES (beans, chickpeas) | 2 | 0.06 |
RICE, PASTA, EGGS | 1.5 | 0.09 |
BREAD | 1 | 0.05 |
PASTRY (cakes, biscuits) | 1-3 | 0.05-0.1 |
FRESH FRUIT, VEGETABLES, MILK, CHEESE | <1 | <0.05 |
Absorption and Excretion
Iron is absorbed above all in the duodenum and proximal jejunum: passively if its concentration in the intestinal lumen is high; through an active process with energy expenditure, if instead it is present in low quantity.
In the cells of the intestinal mucosa Fe2 + is oxidized to Fe3 +.
Part of the iron then passes into the plasma where it is transported in circulation by the transferrin; the remaining portion binds in the cytoplasm of intestinal cells to apoferritin which is converted to ferritin.
From this it is released in relation to the needs of the body and given up to plasma transferrin.
Elimination (1mg per day) occurs mainly with bile, faeces, menstrual blood, peeling of the skin and urine.
Iron Shortage
Although the body limits its losses, cases of iron deficiency are quite common. These may be due to:
- reduced intake, due to diets lacking in meat and rich in cereals;
- insufficient absorption: achlorhydria, diarrhea, gastro-intestinal changes;
- excessive blood loss.
Premature babies, menstruating women, people who have suffered blood loss, alcoholics and vegetarians are at risk of iron deficiency.
Deficiency is manifested by fatigue, fatigue, in severe cases headache, palpitations, neuralgia, vasomotor disorders, ease of infection, iron-free anemia.
Deepening: Iron in Maternal Milk
Considering the nutritional analysis of food and the needs of the newborn, maternal milk seems apparently poor in iron; however the newborn is already born with enough iron supplies to compensate for this deficiency for at least 6 months.
Increasing the mineral intake through enriched artificial milks is not only useless but even counterproductive.
Organisms to survive require iron, including bacteria. Lactobacilli are an exception, they colonize the small intestine at birth and guarantee the baby protection from infection and the digestion of breast milk . The mother transmits little iron from the breast, just to avoid the development of pathogenic bacteria. And this is good, because it hinders the growth of pathogenic bacteria in the intestine at a time when the immune defenses are still immature.
Excess of Iron
If in excess the mineral is transferred to the parenchyma of various organs such as pancreas, adrenal glands, myocardium and liver which are damaged.
The toxicity of iron is called siderosis, a condition almost always of a genetic nature, as in the case of hemochromatosis.
To remember
Interactions with certain drugs that reduce its absorption are known, such as antacids, cholestyramine, anti-inflammatory drugs NSAID inhibitors of COX 1, penicillamine, tetracyclines, some vitamins and some mineral salts.
In vegetable products the iron content decreases by about 15% for cooking with a lot of water and about 10% for steaming (without water).
See also: Iron in food
Iron absorption
