Types of dietary iron
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Types of Dietary Iron: Heme and Nonheme Iron
Dietary iron comes in two main forms: heme iron and nonheme iron. Heme iron is found in animal-based foods, especially meat, poultry, and fish, while nonheme iron is present in plant-based foods, dairy, and eggs, as well as in some animal foods but in smaller amounts. Inorganic forms of iron, such as ferrous and ferric compounds, are also present in the diet, but heme and nonheme iron are the most important for human nutrition 12.
Heme Iron: Sources, Bioavailability, and Health Implications
Heme iron is primarily found in red meat, poultry, and fish. It is more easily absorbed by the body compared to nonheme iron, with bioavailability rates typically higher than those of nonheme iron. This means the body can use heme iron more efficiently 12. However, higher intake of heme iron, especially from red meat, has been linked to an increased risk of type 2 diabetes and cardiovascular disease in several studies 45678. Each 1 mg/day increase in heme iron intake is associated with a higher risk of these conditions, and the risk is particularly notable for heme iron from red meat 45678.
Nonheme Iron: Sources, Bioavailability, and Health Implications
Nonheme iron is found in plant-based foods such as legumes, grains, vegetables, and fortified foods. It is also present in dairy and eggs. The absorption of nonheme iron is generally lower than that of heme iron and is strongly influenced by other dietary factors. For example, vitamin C can enhance nonheme iron absorption, while substances like phytic acid (found in grains and legumes) and certain polyphenols (in tea and coffee) can inhibit it. Cooking, fermentation, and germination can improve nonheme iron bioavailability by reducing inhibitors like phytic acid 12. Unlike heme iron, higher intakes of nonheme iron have not been associated with increased risks of type 2 diabetes or cardiovascular disease 4567.
Total Dietary Iron and Supplemental Iron
Total dietary iron includes both heme and nonheme iron from all food sources. Supplemental iron, found in iron-fortified foods and dietary supplements, is usually in the nonheme form. Studies have not found significant associations between total dietary iron or supplemental iron intake and increased risk of type 2 diabetes or cardiovascular disease 4567.
Conclusion
In summary, dietary iron exists mainly as heme iron (from animal sources) and nonheme iron (from plant and some animal sources). Heme iron is more readily absorbed but is linked to higher risks of type 2 diabetes and cardiovascular disease, especially when consumed in large amounts from red meat. Nonheme iron is less efficiently absorbed and is not associated with these health risks. The bioavailability of both types of iron can be influenced by other dietary components and food preparation methods. Understanding the differences between heme and nonheme iron is important for making informed dietary choices and managing health risks related to iron intake.
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