Iron and Food

Absorption regulation

The maintenance of homeostasis (balance between income and losses) of iron is ensured by the regulation of intestinal absorption, which is increased for the needs of erythropoiesis and reduced when iron stores are abundant.
Iron – rich foods are liver , red meat , oysters and legumes .

Its absorption is reduced in cases of:

• Low-iron diet (in absolute terms, but increases in percentage terms)
• Gastric pH alterations: a reduction in gastric acidity reduces its absorption
• Chelating agents in the diet: substances that bind it, reducing its available amount
• The possible decrease of the absorbent intestinal surface or the alterations of the absorbent cells that constitute it
• Situations of increased intestinal motility
• Hemochromatosis ( hereditary disease)
• Situations that increase iron turnover, such as anemia due to vitamin B12 deficiency (pernicious or nutritional deficiency) or folate
• Metabolic disorders
• Presence in foods of EDTA (a preservative), of Tannates (substances present in tea), of oxalates , phosphates and carbonates.

On the other hand, ascorbic acid ( vitamin C ), citric acid , amino acids and sugars of food origin facilitate its absorption .
Iron is absorbed as heme iron, i.e. bound to hemoglobin or myoglobin present in meat. Or it can be absorbed in soluble (ferrous) form. Heme iron is much more absorbable than inorganic iron .
Absorption occurs at the level of the duodenum (the first portion of the small intestine ) and in the first section of the jejunum (intermediate portion of the small intestine).
The body regulates the amount of iron to be absorbed with three mechanisms:

1. By means of a deposit regulator which signals the de/replenishment status of the deposits themselves.
2. By means of an erythropoiesis regulator, which signals the amount of iron available for erythrocyte synthesis.
3. By a mechanism in the kidney that signals the degree of hypoxia.

Iron in the blood

Iron, once absorbed in the intestine, enters the bloodstream linked to a protein called transferrin , and here it is found in a closed system where it is constantly recycled between plasma and tissues.
In clinical practice it is very useful to dose:

The amount of circulating transferrin saturated in iron , a value which takes the name of sideremia , and whose normal values ​​are between 15 and 120 milligrams per decilitre.

The total iron binding capacity, which takes the name of transferrinemia , and whose normal values ​​are between 250 and 400 milligrams per decilitre.

Transferrin plays a key role in hematopoiesis, as it is responsible for transferring iron to erythroblasts , which have a specific receptor for it on their surface.

Iron losses

The physiological excretion of iron occurs with urine, faeces, sweat , desquamation of intestinal cells, skin, urinary tract. Iron losses in men and women after menopause amount to about 1 mg per day. In women of childbearing age, losses are increased in consideration of the menstrual cycle (normally up to about 25 mg/cycle) and pregnancies, since, from conception to delivery, there is an additional iron loss of about 700 mg, if they consider the quotas transferred to the fetus , the expulsion of the placenta and the post-partum hemorrhage; the loss due to breastfeeding is about 1 mg per day.

Iron metabolism

Under normal conditions, the iron content of the whole body varies from 2 g in women to 6 g in men. The iron is divided into a functional compartment and a storage compartment. About 80% of functional iron is found in hemoglobin, myoglobin and iron-providing enzymes. In the storage pool, consisting of hemosiderin and ferritin , about 15% of the total iron is found. It should be noted that young women, even in good health, have significantly lower iron stores than men. Their martial balance (of iron) is therefore much more precarious and they are consequently more vulnerable to excessive losses or to the increase in demands connected with the menstrual cycle and pregnancy .
All the stored iron is stored in the form of ferritin or hemosiderin . Ferritin is essentially an iron-protein complex found in all tissues, but particularly in the liver , spleen , bone marrow and skeletal muscle .
When iron stores are normal, only traces of hemosiderin are found in the body. It is formed by aggregates of ferritin molecules. Under conditions of iron overload, most of the iron is stored in the form of haemosiderin .
Usually in the plasmavery small amounts of ferritin circulate. Plasma ferritin largely derives from the depot pool and therefore its dosage is a good index of the adequacy of the body’s martial reserves. In situations of deficiency, serum ferritin is always lower than 12 micrograms per litre, while in conditions of overload, very high values ​​can also be found, close to 5,000 micrograms per litre.
The physiological importance of the martial reserve pool consists in the ease of mobilization in case of an increase in requests.
Under normal conditions, there is an equilibrium between the amount of ferritin in the deposits and that in the plasma. This is a useful parameter to evaluate the martial reserves of the organism.
There are a few situations in which iron deposits grow:

In case of overload resulting from a high intake of iron, such as for example in subjects who need continuous blood transfusions or in those affected by a genetic disease called haemosiderosis .

In chronic inflammatory processes or tumors, in which the iron is carried from the circulating (usable) compartment to that of the deposits, with a consequent picture of anemia of chronic diseases, characterized by a reduction of the circulating iron (hypoderemia) and by an increase of that deposit (hyperferritinemia).

Important tissue destructions: they lead to a release into the circulation of the iron contained in the damaged cells with a consequent increase in circulating ferritin.