Iron

Iron is an essential trace element that serves numerous critical functions in human physiology. As a core component of hemoglobin and myoglobin, iron enables oxygen transport from the lungs to tissues and oxygen storage in muscles. It is also a cofactor for numerous enzymes involved in energy production, DNA synthesis, and immune function.

The body tightly regulates iron homeostasis through absorption, storage, and recycling mechanisms. Dietary iron comes in two forms: heme iron (from animal sources, highly bioavailable) and non-heme iron (from plant sources, less bioavailable and affected by other dietary components).

Iron deficiency represents the most common nutritional deficiency globally, affecting approximately 30% of the world's population. Risk factors include menstrual blood loss, pregnancy, vegetarian/vegan diets, gastrointestinal disorders, and certain chronic diseases. Iron deficiency anemia develops when iron stores are depleted and hemoglobin synthesis is impaired.

Clinical research demonstrates that iron supplementation effectively corrects deficiency anemia and improves fatigue, physical performance, and quality of life in deficient individuals. However, because excessive iron accumulation can be toxic, supplementation should be guided by healthcare providers, particularly for men and postmenopausal women who have lower iron requirements.

Iron serves as an essential component of heme, the prosthetic group in hemoglobin and myoglobin. In hemoglobin, iron binds oxygen in the lungs and releases it to tissues throughout the body. Myoglobin stores and releases oxygen in muscle cells, facilitating oxygen availability during physical activity.

Beyond oxygen transport, iron is a cofactor for numerous enzymes involved in energy metabolism, including those in the electron transport chain for ATP production. Iron-dependent enzymes are also required for DNA synthesis, cell division, and neurotransmitter synthesis.

Iron absorption occurs primarily in the duodenum and proximal jejunum. Heme iron (from animal sources) is absorbed directly via heme transporters with approximately 15-35% bioavailability. Non-heme iron (from plant sources) requires reduction to ferrous iron (Fe²⁺) before absorption via the divalent metal transporter 1 (DMT1), with bioavailability of 2-20% depending on dietary enhancers and inhibitors.

Vitamin C (ascorbic acid) enhances non-heme iron absorption by reducing ferric iron (Fe³⁺) to the more soluble ferrous form and forming a chelate that remains soluble in the alkaline intestinal environment. Conversely, phytates (in whole grains), polyphenols (in tea and coffee), and calcium can inhibit iron absorption.

Iron is found in both animal and plant foods. Heme iron from animal sources (meat, poultry, seafood) is more readily absorbed than non-heme iron from plant sources (beans, lentils, spinach). Vitamin C-rich foods enhance absorption of non-heme iron when consumed together.

Iron deficiency progresses through stages: depletion of iron stores (reduced ferritin), followed by decreased iron transport (low serum iron, high transferrin), and finally iron deficiency anemia (low hemoglobin, microcytic red blood cells). Symptoms include fatigue, weakness, pale skin, shortness of breath, dizziness, cold hands and feet, brittle nails, and cravings for non-food items (pica).

Iron requirements vary significantly based on age, sex, and physiological status. Women of childbearing age have substantially higher needs due to menstrual losses. Pregnant women require the highest amounts to support fetal development and maternal blood volume expansion.

Iron supplements come in various forms with differing elemental iron content and absorption rates. Ferrous iron (Fe²⁺) forms are better absorbed than ferric iron (Fe³⁺). Enteric-coated or slow-release forms may reduce gastrointestinal side effects but could decrease absorption.