Iron role in the body
Iron is one of the most important and essential microelements present in the human body, namely as a part of iron-containing enzymes such as hemoglobin and myoglobin. As a part of hemoglobin, Ferrum binds the oxygen and carries it throughout the body to the tissues. Iron also plays an important role in the cytochrome system of the mitochondria – power plant of the cell. The nonactive pool of iron is represented by the storage proteins ferritin, hemosiderin, and transferrin.
Metabolism of iron
Iron is absorbed in the gastrointestinal tract (mainly in the duodenum and proximal part of the small intestine) into the bloodstream where it bounds with the special iron transport protein called transferritin. This complex circulates in the body until it reaches the bone marrow where through the interaction with transferritin receptors the iron is transported into the erythroid cells where the heme synthesis takes place. Not all of the body’s iron is involved in hemoglobin synthesis – the inactive iron is bound to the so-called storage protein apoferritin forming the substance known as ferritin.
The life span of an average red blood cell containing iron is about 120 days. Every day about 1% of the erythrocytes are destroyed in the cells of the reticuloendothelial system, the hemoglobin is broken down and released iron binds with transferrin and travels to bone marrow again.
Dietary reference intake
The recommended dietary intake of iron is approximately 8 mg of iron per day for men and women after menopause. Women of childbearing age require higher doses of iron as they are prone to develop iron deficiency due to chronic blood loss, therefore they should receive about 18 mg of iron per day. Even higher are iron requirements during pregnancy due to high usage of iron by the cells – 27 mg/day.
Infant and young children require about 7-11 mg/day, whether older children and adolescents – up to 15 mg/day.
Foods with a high content of iron
A common mixed diet contains about 6 mg of iron per 1000 calories.
The listed products are the main sources of iron in a diet:
- Meat (beaf or chicken liver, kidney, heart, lean beef, chicken, turkey, lamb, pork, ham);
- Seaproducts (oysters, shellfish, sardines, salmon, tuna);
- Egg yolk;
- Legumes (beans, chickpeas, peas, soybeans, and lentils);
- Potatoes and rice;
- Cashew and pumpkin seeds;
- Spinach, silverbeet, and broccoli;
- Blueberries and dried fruits;
- Dark chocolate;
- Iron-containing breakfast cereals, whole grains wheat;
The liver is considered to be the best dietary source of iron followed by seafood, meat, and poultry. Plant sources of iron are represented by the dried beans and vegetables, dried fruits, whole grains, and cereals.
However, not all the ingested iron is being absorbed; availability of the dietary iron is an important and not well-understood question. Various factors can influence the bioavailability of iron including the nature of the foodstuff. For example, in general, iron derived from the red meat (so-called heme iron) is readily absorbed in the digestive tract, while on the other hand only 5% of non heme iron or even less can be absorbed from the vegetables. The absorption of non heme iron seems to depend on the production of hormone hepcidin by the liver that is influenced by the filling of the body’s iron storage – the absorption will be higher when iron stores are depleted and vice versa.
Furthermore, the foods you consume with iron-rich products also matter. Coffee and tea are known to reduce iron absorption so it is recommended to drink these beverages rather in-between the meals. What’s more, wheat brans and soy products may inhibit the absorption of nonheme iron, therefore, consumption of soy should be carefully regulated.
Vitamin C enhances Ferrum absorption so vitamin C containing products (potatoes, tomatoes, cabbage, spinach, broccoli, grapefruit, strawberries, oranges) may be especially helpful if consumed with nonheme iron sources. On average, iron bioavailability varies from 5 to 15%, though sometimes it may reach even 50% in severely deficient individuals.