Nonheme Iron

Nonheme iron is dietary iron that is not incorporated into a heme molecule. It is one of the two major forms of dietary iron, the other being heme iron. Nonheme iron is the form present in plant foods and iron-fortified foods, and it is also present in animal-derived foods, which can contain both heme and nonheme iron .¹

Nonheme iron can occur in several chemical forms, including ferric and ferrous iron compounds and iron associated with proteins such as ferritin. For soluble inorganic nonheme iron, intestinal absorption occurs mainly in the duodenum. Ferric iron (Fe3+) is generally reduced to ferrous iron (Fe2+) at or near the intestinal surface before Fe2+ is transported into enterocytes through divalent metal transporter 1 (DMT1) .²

The amount of nonheme iron absorbed varies considerably according to both meal composition and the body's iron status. Ascorbic acid, or vitamin C, can increase nonheme iron absorption, partly by helping maintain iron in a soluble, reduced form. In contrast, compounds such as phytate and certain polyphenols can bind iron and reduce its availability for absorption. Systemic regulation, particularly through the hormone hepcidin, also influences how much absorbed iron enters the circulation .^1,2

Nonheme iron differs from heme iron in both chemical form and absorption. Heme iron is contained within a porphyrin structure and is generally more bioavailable, with its absorption less strongly affected by other dietary components. Nonheme iron therefore describes a chemical and nutritional form of iron rather than a particular food source .^1,2