Understanding the process of iron absorption in the body is key to grasping its mechanism of action. The disparity in absorption between heme and non-heme iron has implications for the amount of elemental iron absorbed in the body, with heme iron, typically found in animal products, being absorbed more efficiently.[1]
Both heme and non-heme iron are primarily absorbed in the duodenum and, to a lesser extent, in the upper jejunum (the first and second sections of the small intestine, respectively). Heme iron enters the gastrointestinal tract as ferrous iron (i.e., with a 2+ oxidation state), which is more easily absorbed, while non-heme iron is typically ingested in its ferric (3+) form. However, for non-heme iron to be absorbed, it must first be reduced into ferrous iron by reductase enzymes (e.g., ascorbate ferrireductase), or other compounds like vitamin C. Ferrous iron is then taken up by enterocytes lining the intestine through the divalent metal transporter 1 (DMT1), and then leaves these cells and enters the bloodstream via ferroportin. Once in the bloodstream, iron is converted back from ferrous to ferric iron and transported by transferrin to various organs and tissues.[2]
After absorption, iron plays a crucial role in several reactions and biological processes within the body, many of which are centered around iron’s roles in protein function and oxygen transport and storage. Iron is required to form hemoglobin (an oxygen-transporter protein) and myoglobin (an oxygen-storage protein). Inadequate iron intake can hinder the production of healthy red blood cells, potentially leading to anemia. In mitochondria, iron serves as a cofactor in proteins that contain iron-sulfur clusters (e.g., flavoproteins), other heme-containing proteins involved in the electron transport chain (e.g., cytochrome c oxidase), and proteins that contain iron ions (e.g., monooxygenases and dioxygenases).[3][4] Additionally, iron is involved in cell growth and differentiation, electron transfer reactions for energy production, and the regulation of the expression of some genes.[5]
Iron is also an essential nutrient for brain development and function. It plays a role in energy (ATP) production and neurotransmitter synthesis, as well as in the uptake and degradation of neurotransmitters, all of which are involved in behavior, memory, learning, and sensory systems.[6][7]
It’s important to note that when iron supplements are taken to treat IDA, it usually takes about 3 months to replenish iron stores, and hemoglobin levels will increase gradually in the first month of supplementation.[8]