Iron is essential for a functioning immune system. It fuels the production of infection-fighting white blood cells, powers the killing mechanisms that destroy bacteria, and supports the rapid cell division your body needs to mount an immune response. But the relationship between iron and immunity is more nuanced than “more is better.” Your body carefully controls iron levels, and both too little and too much can leave you vulnerable to infection.
How Iron Powers Immune Cells
Iron is used by roughly 400 proteins in the body, with over 200 of those active in T cells, the white blood cells that coordinate your immune response and kill infected cells. These proteins handle everything from energy production inside mitochondria to DNA synthesis and repair. When iron runs low, the impact on immune cells is broad and deep.
The most striking effect shows up in CD8+ T cells, the immune cells responsible for directly killing virus-infected or cancerous cells. When iron is scarce, these cells activate normally, growing in size and switching on their surface markers as expected. But then they stall. They cannot proliferate. The problem traces back to mitochondria, where iron-dependent enzymes drive the energy cycle that produces a molecule called aspartate. Without enough aspartate, cells can’t build the DNA building blocks (purines and pyrimidines) they need to divide. The result is a T cell that recognizes a threat but can’t multiply fast enough to fight it off.
Iron deficiency also changes the chemical landscape inside these cells. Histone methylation, which controls which genes get switched on or off, becomes altered. Mitochondrial membrane potential drops. Glucose and glutamine processing slows and partially reverses direction. These aren’t subtle tweaks; they represent a fundamental disruption to how the cell generates energy and builds new copies of itself.
Iron’s Role in Killing Bacteria
Your first-responder immune cells, neutrophils, rely on iron to destroy bacteria they’ve engulfed. They use two main weapons: an enzyme called myeloperoxidase and a rapid surge in oxygen consumption known as the oxidative burst. Both are iron-dependent. In iron-deficient individuals, myeloperoxidase activity drops significantly, reducing the cell’s ability to generate the toxic compounds that kill ingested microbes. The oxidative burst is also suppressed, though to a lesser degree.
Macrophages, the larger immune cells that patrol tissues and clean up infections, also depend on iron status to function properly. When activated against intracellular pathogens like Salmonella, macrophages deliberately export iron out of the cell and block new iron from entering. This starves the bacteria trapped inside. Macrophages that can’t execute this iron-shuttling strategy show impaired resistance to infection.
Your Body Hides Iron During Infection
One of the most fascinating aspects of iron and immunity is a strategy called nutritional immunity. When you get an infection, your body actively pulls iron out of your bloodstream to keep it away from invading bacteria. The key player is hepcidin, a hormone produced by the liver. During inflammation, immune signaling molecules trigger a surge in hepcidin, which blocks the only known iron export channel on cells. This traps iron inside your cells and causes a rapid drop in circulating iron levels.
This matters because bacteria need iron to survive and multiply, and they’ve evolved aggressive tools to get it. Many bacterial species secrete molecules called siderophores that bind iron with an affinity far higher than your own iron-carrying proteins. These siderophores can strip iron from your body’s transport molecules and deliver it directly to the pathogen. Your immune system fights back: neutrophils and macrophages release a protein called lipocalin 2 that intercepts iron-loaded siderophores before bacteria can reclaim them.
Some pathogens have evolved countermeasures. Certain strains of E. coli produce chemically modified siderophores that lipocalin 2 can’t bind. Klebsiella pneumoniae, a common cause of respiratory infections, produces a siderophore that naturally evades this defense. The evolutionary arms race over iron access is one of the oldest and most intense battles between humans and infectious microbes.
The hepcidin response has been directly tested in animal models of pneumonia. Mice that couldn’t produce hepcidin during a lung infection experienced a paradoxical rise in blood iron levels and developed severe bloodstream infections as bacteria spread from the lungs. Normal mice, whose hepcidin kicked in as expected, kept plasma iron low and contained the infection to the lungs. Hepcidin-driven iron sequestration is essential for preventing bacteria from escaping a local infection and going systemic.
Iron Deficiency and Infection Risk
The clinical consequences of low iron are measurable. A study of over 2,000 adults aged 70 and older found that iron deficiency was associated with a 63% greater rate of severe infections requiring hospitalization. Among participants who were iron-deficient but not yet anemic, the risk was even higher: an 80% increase in hospitalizations for infection compared to those with normal iron levels. This is significant because it suggests immune impairment begins before iron levels drop low enough to cause anemia.
The picture in children is equally concerning. Iron deficiency or anemia at the time of vaccination predicts weaker immune responses to diphtheria, pertussis, and pneumococcal vaccines in African infants. Iron supplementation may improve the response to measles vaccination. Iron is critical for the B cells that produce antibodies; sufficient iron supports the production of both the antibody-secreting cells and the antibodies themselves. A child vaccinated while iron-deficient may not build the same level of protection as one with adequate iron stores.
Why More Iron Isn’t Always Better
Given iron’s importance, it might seem logical to supplement heavily. But excess iron creates its own immune problems. Free iron that isn’t bound to proteins can generate oxidative radicals that damage cells, proteins, and DNA. More critically, extra circulating iron feeds the very pathogens your body is trying to starve.
Iron supplementation in tropical regions has been linked to increased rates of malaria and tuberculosis. Iron overload conditions, whether from genetic disorders, excessive dietary intake, or abnormal red blood cell breakdown, are also associated with heightened susceptibility to these infections. This is consistent with the nutritional immunity concept: your body deliberately lowers available iron during infection, so flooding the system with supplemental iron can work against that protective response.
The study in older adults captured this complexity. Among participants who already had anemia at baseline, iron deficiency was actually associated with a 26% lower rate of overall infections and 37% fewer upper respiratory infections. One interpretation is that in the context of chronic inflammation (which often causes anemia), lower circulating iron may offer some protection against certain pathogens even as it raises the risk of severe, hospitalized infections. The relationship between iron and immunity is not a simple linear curve.
Getting Iron Right for Immune Health
The practical takeaway is that your immune system needs iron, but it needs the right amount. Iron deficiency, even without full-blown anemia, can impair T cell proliferation, weaken neutrophil killing power, reduce vaccine effectiveness, and increase your risk of serious infection. At the same time, excess iron can feed pathogens and cause oxidative damage.
If you suspect low iron, a blood test measuring ferritin (your iron storage protein) is more informative than hemoglobin alone, since immune impairment can begin before anemia develops. Iron from animal sources (heme iron) is absorbed more efficiently than plant-based (non-heme) iron, and vitamin C taken alongside iron-rich foods improves absorption of the plant-based form. For people with confirmed deficiency, supplementation can restore neutrophil function, though different immune functions recover at different rates. Myeloperoxidase activity, for instance, takes longer to normalize than the oxidative burst after iron treatment begins.