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Iron is a vital mineral that your body uses for many essential functions, from making energy in your cells to helping your brain work properly. But its most well-known role is in oxygen transport; iron is a key part of hemoglobin, the protein in red blood cells that carries oxygen from your lungs to the rest of your body. Nearly two-thirds of the body’s iron is found in these red blood cells. The rest is stored in the liver, spleen, bone marrow, and muscles, where it supports myoglobin (which stores oxygen in muscle tissue) and a variety of enzymes involved in DNA synthesis, mitochondrial energy production, and immune function.
Iron is also critical for brain health. It’s needed for the creation of myelin (the protective sheath around nerves), proper neurotransmitter cycling (especially dopamine and serotonin), and healthy mitochondrial activity in neurons. Without enough iron, you may experience cognitive changes, fatigue, or restless legs. But too much iron can be dangerous as well. Iron accumulation in the brain or organs can generate oxidative stress, damaging cells and possibly contributing to conditions like Alzheimer’s disease, liver fibrosis, and heart failure.
Iron homeostasis is tightly controlled, primarily at the point of absorption in the small intestine. Unlike many nutrients, the body has no active way to excrete excess iron, so balance is maintained by adjusting how much iron gets absorbed from food. The key regulator here is hepcidin, a hormone made by the liver. When iron levels are high, hepcidin tells cells to stop absorbing more. It does this by blocking ferroportin, the protein that exports iron into the bloodstream. When iron is low, hepcidin drops, allowing more absorption.
Iron deficiency is the most common nutritional deficiency worldwide. It can happen due to chronic blood loss (like heavy menstrual periods or internal bleeding), low dietary intake, or problems with absorption (as in celiac disease or post-bariatric surgery). Inflammation and obesity can also block iron absorption, leading to what’s called functional iron deficiency, when stores exist, but they can’t be mobilized effectively.
Deficiency progresses in stages: first, your body uses up stored iron (low ferritin); next, the amount of circulating iron and transferrin saturation drops; eventually, hemoglobin falls and anemia develops. Even before anemia, people may experience fatigue, poor focus, irritability, and cold intolerance.
Iron supplements, especially oral iron, are commonly used to correct deficiency. But not all strategies are equally effective. Daily iron dosing can actually increase hepcidin and reduce absorption. Research shows that alternate-day dosing may optimize iron uptake, especially in women of reproductive age.
In cases where oral iron fails (e.g., in heart failure, inflammatory bowel disease, or chronic kidney disease), intravenous (IV) iron is often more effective. IV iron works faster and bypasses the gut entirely. While generally safe, IV iron carries a small risk of infusion reactions and infections, so it’s reserved for more severe cases.
In chronic diseases like heart failure, iron deficiency (even without anemia) can worsen symptoms and outcomes. Correcting iron status improves energy levels and exercise capacity. Children with obesity often have iron deficiency due to chronic low-grade inflammation, not dietary lack, highlighting the need for nuanced diagnosis and treatment.
Excess iron, especially from heme iron (found in red meat), may also raise the risk of some cancers. Heme iron can act as a pro-oxidant, promoting damage to DNA and cell membranes.
Just as too little iron can impair health, too much can be toxic. Primary iron overload is usually inherited, as in hereditary hemochromatosis (most often caused by mutations in the HFE gene). Secondary iron overload can occur from frequent blood transfusions or long-term high-dose supplementation.
Iron overload causes damage by generating reactive oxygen species (ROS), unstable molecules that harm cells. The liver, heart, pancreas, and endocrine glands are particularly vulnerable. Complications include liver cirrhosis, diabetes, heart failure, and infertility.
Treatment for iron overload typically involves phlebotomy (regular blood removal) or iron chelation therapy (drugs that bind and remove iron). Patients should also avoid vitamin C supplements (which enhance iron absorption) and iron-containing multivitamins.
During pregnancy, iron needs increase significantly to support fetal growth, brain development, and the expansion of maternal blood volume. Iron supplementation during pregnancy reduces the risk of low birth weight and anemia, but its effect on preventing preterm birth is still being studied. While iron is essential for infant brain development, the evidence on whether supplementation improves developmental outcomes is mixed.