Does iron deficiency impair immune function and raise infection risk?

Iron is a fundamental micronutrient that acts as a critical cofactor for enzymes involved in DNA synthesis, cellular metabolism, and the antimicrobial response. Its deficiency creates a state of metabolic constraint that compromises both the innate and adaptive immune systems.

Clinical evidence and effectiveness

Clinical observations consistently link iron deficiency to a heightened risk of morbidity from infections, particularly in respiratory and gastrointestinal domains.

• Lymphocyte Response: Research indicates that iron-deficient individuals often exhibit reduced T-cell counts and impaired delayed-type hypersensitivity responses. This is primarily due to the inability of lymphocytes to expand rapidly enough to mount an effective defense during a pathogen challenge.
• Epidemiological Links: Large-scale studies show that correcting iron deficiency can reduce the frequency and severity of infections in vulnerable populations, such as children and women of reproductive age.
• Risk Complexity: While deficiency impairs the host, it is important to note that many pathogens also require iron to replicate. Consequently, the relationship between iron status and infection is a "double-edged sword," where both extreme deficiency and excessive iron availability (particularly non-transferrin-bound iron) can negatively influence infection outcomes.

Mechanistic explanations

The immune impairment seen in iron deficiency is driven by specific cellular and molecular failures:

• DNA Synthesis: Ribonucleotide reductase, the enzyme responsible for the rate-limiting step in DNA synthesis, requires a diferric-tyrosyl radical cofactor. When iron is scarce, this enzyme's activity drops, directly stalling the proliferation of T-lymphocytes.
• Oxidative Killing: Neutrophils and macrophages rely on iron-containing enzymes, such as myeloperoxidase (MPO), to produce the "oxidative burst" (reactive oxygen species) necessary to kill phagocytosed bacteria.
• Cellular Signaling: Iron deficiency disrupts the functional polarization of macrophages, reducing their ability to present antigens via MHC class II and diminishing the production of critical cytokines like interferon-gamma, which are essential for antiviral responses.

Bottom line

Iron deficiency significantly impairs immune function by stalling lymphocyte proliferation and weakening the bactericidal activity of innate immune cells. While this mechanistically increases susceptibility to various infections, clinical management must balance correcting deficiency with the risk that excess iron can also promote pathogen growth.