The master regulator of systemic iron homeostasis. Hepcidin is a 25-amino-acid peptide hormone produced primarily by hepatocytes that controls iron absorption, recycling, and distribution by binding to and degrading ferroportin (SLC40A1/FPN) -- the only known cellular iron exporter. Understanding hepcidin is essential for interpreting the iron supplementation paradox that recurs across multiple disease contexts in this wiki.
Mechanism of Action
The Hepcidin-Ferroportin Axis
- Hepcidin binds ferroportin on the surface of enterocytes, macrophages, and hepatocytes, triggering its internalization and degradation [bao 2024 iron homeostasis intestinal immunity gut microbiota].
- When hepcidin is high: ferroportin is destroyed, iron is trapped inside cells, serum iron falls.
- When hepcidin is low: ferroportin is expressed, iron flows into plasma from dietary absorption and macrophage recycling.
Regulation
- Iron excess upregulates hepcidin via the BMP-SMAD pathway (bone morphogenetic protein signaling).
- Inflammation upregulates hepcidin via IL-6/JAK-STAT3 signaling -- this is the basis of anemia of chronic disease.
- Iron deficiency and erythropoietic demand suppress hepcidin to increase iron availability.
- Hypoxia suppresses hepcidin via HIF signaling.
Hepcidin and Nutritional Immunity
Elevated hepcidin during infection represents the host INTENTIONALLY restricting iron availability -- a key arm of nutritional immunity. This has profound clinical implications:
The Iron Supplementation Paradox
- In inflammatory states (IBD, chronic infection, autoimmune disease), hepcidin is elevated and serum iron/ferritin may appear low.
- Clinicians interpret low iron markers as deficiency and prescribe iron supplementation.
- However, high hepcidin means supplemental iron is poorly absorbed (blocked at the enterocyte) and what IS absorbed may feed iron-requiring pathogens rather than reaching the host's erythroid compartment.
- Unabsorbed oral iron reaches the colon, where it feeds siderophore-producing Enterobacteriaceae and disrupts the gut microbiome [bao 2024 iron homeostasis intestinal immunity gut microbiota].
Infection Context
- Hepcidin elevation during infection is part of a coordinated host defense that includes lactoferrin (iron sequestration at mucosal surfaces), ferritin (intracellular iron storage), and transferrin (limiting free plasma iron).
- Vaginal lactoferrin concentrations positively correlate with serum hepcidin levels, suggesting coordinated systemic and mucosal iron restriction during infection [roberts 2019 lactoferrin genital infections iron].
Hepcidin in Disease Contexts
Chronic Kidney Disease
- Hepcidin accumulates in CKD due to reduced renal clearance and chronic inflammation, contributing to the anemia of CKD and functional iron deficiency [mishra 2022 molecular mechanisms heavy metals ckd].
- Iron supplementation in CKD patients with elevated hepcidin may be ineffective or harmful.
Neurodegeneration
- Disruption of the hepcidin-ferroportin axis in the brain contributes to regional iron accumulation (substantia nigra in PD, hippocampus in AD), increasing ferroptosis vulnerability [pendergrass 2026 microbial metallomics parkinsons ferroptosis].
Thyroid Disease
- Hepcidin dysregulation has been documented in autoimmune thyroid disease, linking iron homeostasis to thyroid function [brylinski 2025 trace elements thyroid diseases].
Clinical Significance
Hepcidin measurement should ideally guide iron supplementation decisions: supplementing iron when hepcidin is high is at best ineffective and at worst feeds pathogens and worsens dysbiosis. This principle is violated daily in clinical practice because hepcidin is not part of standard iron panels.
Connections
- iron -- hepcidin is the master regulator of iron homeostasis
- nutritional immunity -- hepcidin-mediated iron restriction is a core host defense
- ferroptosis -- hepcidin dysregulation contributes to iron-driven cell death
- lactoferrin -- coordinated mucosal iron restriction
- gut metal microbiome -- unabsorbed iron from supplementation feeds pathobionts