Dietary sources of iron
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Types of Dietary Iron: Heme and Non-Heme Iron Sources
Iron in the diet comes in two main forms: heme iron and non-heme iron. Heme iron is found in animal-based foods such as red meat, poultry, seafood (especially oysters and clams), liver, kidneys, and eggs. Non-heme iron is present in both plant and animal foods, but is especially abundant in plant-based sources like beans, peas, nuts, leafy green vegetables (such as spinach), enriched pastas and breads, fortified cereals, and certain fruits including watermelon, raisins, strawberries, dates, figs, dried apricots, peaches, and prunes or prune juice 129.
Major Dietary Sources of Iron: Animal and Plant Foods
Animal sources, which provide heme iron, include red meat, poultry, seafood, and eggs. These sources are generally more efficiently absorbed by the body compared to plant sources. Plant-based sources, which provide non-heme iron, include beans, peas, nuts, leafy greens, cereals, grains, and fortified foods. Among plant foods, beans have been shown to have particularly high iron content, followed by fish, eggs, and pork among animal sources 126.
In various populations, bread, cereals, grains, and vegetables are significant contributors to total iron intake, with cereals or grains often providing the largest share, followed by meats and vegetables 348. In young children, infant formulas and cereals are the main sources of iron, while meat contributes a smaller portion .
Iron Bioavailability and Absorption from Dietary Sources
The body absorbs heme iron from animal sources more efficiently than non-heme iron from plant sources. The absorption rate for iron from food can vary widely, from about 1% to 40%, depending on the form of iron, the body's needs, and other dietary factors 129. Mixed diets (containing both animal and plant foods) have an iron bioavailability of 14–18%, while vegetarian diets have a lower bioavailability of 5–12% .
Iron absorption is also influenced by other components in the diet. Meat proteins and organic acids can enhance iron absorption, while phytates (found in whole grains and legumes), calcium, and polyphenols (found in tea and coffee) can inhibit it. Food preparation methods like cooking, fermentation, and germination can improve the bioavailability of non-heme iron by reducing inhibitors such as phytic acid 29.
Population-Specific Iron Sources and Intake Patterns
Studies in different countries show that the main sources of dietary iron can vary. In Armenia and Spain, bread, cereals, grains, fruits, and vegetables are the primary sources, with heme iron making up a small fraction of total intake 34. In Poland, adolescent females get most of their iron from non-heme sources, especially if they follow vegetarian diets . In France, young children rely heavily on iron-fortified formulas and cereals for their iron intake, with meat playing a smaller role .
Special Forms of Dietary Iron: Ferritin and Fortified Foods
Ferritin, a form of non-heme iron found in legumes like soybeans, is a natural alternative for iron supplementation and may be useful in addressing iron deficiency, especially where traditional supplements are less acceptable or have side effects . Fortified foods, such as iron-enriched rice, flour, and biscuits, are also important sources of dietary iron, especially in populations at risk of deficiency .
Conclusion
Dietary iron is found in a wide variety of foods, with animal sources providing heme iron and plant sources providing non-heme iron. The main contributors to iron intake in most populations are cereals, grains, vegetables, and meats, with fortified foods and formulas playing a key role for young children. The body absorbs heme iron more efficiently, but the overall absorption of iron depends on dietary composition and preparation methods. Understanding these sources and factors is essential for preventing iron deficiency and ensuring adequate iron intake across different age groups and dietary patterns.
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