Can chronic low-grade inflammation from metabolic dysfunction or autoimmunity cause functional iron deficiency?

The physiological link between chronic low-grade inflammation and restricted iron availability—often termed "functional iron deficiency"—is well-supported by clinical and mechanistic evidence. This process is driven primarily by the interaction between the cytokine interleukin-6 (IL-6) and the iron-regulatory hormone hepcidin.

The IL-6/Hepcidin Axis

Sustained IL-6 signaling is a primary driver of elevated hepcidin.

• Mechanistic Pathway: IL-6 binds to its receptor complex, activating the Janus kinase (JAK) and Signal Transducer and Activator of Transcription 3 (STAT3) pathway. Phosphorylated STAT3 translocates to the nucleus and directly binds to the promoter of the HAMP gene, which encodes hepcidin.
• Transcriptional Control: Experimental models confirm that IL-6 is both necessary and sufficient for inflammation-induced hepcidin elevation; blocking IL-6 or the STAT3 pathway effectively reverses hepcidin induction, even during active inflammation.

Metabolic and Autoimmune Triggers

Chronic inflammation originating from metabolic dysfunction and autoimmunity provides the continuous cytokine stimulus required for this axis.

• Metabolic Dysfunction: In obesity and insulin resistance, adipose tissue macrophages shift toward a pro-inflammatory M1 phenotype, becoming a significant source of systemic IL-6.
• Autoimmune Activity: Conditions like Hashimoto’s thyroiditis induce endoplasmic reticulum (ER) stress and regulatory T cell (Treg) depletion, further elevating IL-6 levels. This creates a self-sustaining cycle where inflammation and metabolic impairment reinforce each other.

Iron Restriction in the Bone Marrow

Elevated hepcidin limits iron availability by targeting ferroportin, the only known cellular iron exporter.

• Ferroportin Degradation: Hepcidin binds to ferroportin on the surface of macrophages and enterocytes, triggering its internalization and degradation. This sequesters iron within these cells, preventing its release into the circulation.
• Bone Marrow Supply: This sequestration causes hypoferremia (low serum iron) and low transferrin saturation (TSAT). Research shows a strong inverse correlation between hepcidin levels and bone marrow sideroblasts, confirming that high hepcidin restricts the iron available for erythropoiesis (red blood cell production), regardless of total body iron stores.

Bottom line

Chronic low-grade inflammation from metabolic or autoimmune sources sustains IL-6 signaling, which keeps hepcidin elevated via the JAK/STAT3 pathway. This results in the degradation of ferroportin and the sequestration of iron in storage cells, effectively starving the bone marrow of the iron required for healthy red blood cell production.