Nonheme

Nonheme refers to substances that do not contain a heme group, the iron-containing porphyrin found in hemoglobin and several other proteins. In chemistry and biology, nonheme iron denotes iron not bound within a heme moiety. It is a central component of many metalloproteins, including iron-sulfur proteins and a variety of nonheme iron enzymes, as well as iron storage and transport proteins such as ferritin and transferrin.

In nutrition, nonheme iron is the form of iron most abundant in plant-based foods and iron-fortified products. Heme iron, by contrast, is primarily found in animal tissues. Nonheme iron is generally less readily absorbed by the digestive tract, and its uptake is influenced by dietary components. Absorption is enhanced by stomach acid and vitamin C, while inhibitors include phytates, polyphenols, and calcium.

Once absorbed, iron proceeds through the bloodstream bound to transferrin, is delivered to tissues, and is stored mainly as ferritin or ferritin-bound iron in the liver, spleen, and bone marrow. Its levels are regulated by hormonal controls such as hepcidin, which modulates intestinal absorption and iron release from stores.

Deficiency of nonheme iron can contribute to iron deficiency anemia, especially in populations relying heavily on plant-based diets or with conditions that impair absorption. Assessment of iron status commonly includes measurements of serum ferritin, transferrin saturation, and serum iron. Excess iron, including nonheme iron, can be toxic in overload conditions.