Does inflammation raise hepcidin and cause functional iron restriction?

Inflammation initiates a complex physiological response that significantly alters iron metabolism, a process termed "nutritional immunity" or "anemia of inflammation." This phenomenon is characterized by the body’s attempt to sequester iron to limit its availability to pathogens.

Clinical and effectiveness evidence

In states of systemic inflammation—such as chronic kidney disease, rheumatoid arthritis, or acute infections—the clinical profile of iron status changes dramatically.

• Serum Iron and TSAT: Diagnostic guidelines (e.g., ESC 2023, KDIGO) define functional iron restriction by a transferrin saturation (TSAT) of <20%. This reflects a deficit in circulating iron available for physiological processes like red blood cell production.
• Ferritin Levels: Unlike absolute iron deficiency (where ferritin is typically <30 μg/L or <100 μg/L depending on context), functional restriction presents with normal or elevated ferritin levels, often ranging from 100 μg/L to over 300 μg/L.
• The Contrast: Clinical evidence confirms that low TSAT in the presence of high ferritin is a hallmark of inflammation-induced iron sequestration, distinguishing it from true iron depletion.

Mechanistic explanations

The link between inflammation and restricted iron availability is mediated by the hormone hepcidin, the master regulator of systemic iron.

• Hepcidin Induction: Pro-inflammatory cytokines, specifically Interleukin-6 (IL-6), trigger the JAK/STAT3 signaling pathway in the liver. This directly upregulates the transcription of the HAMP gene, leading to a rapid surge in serum hepcidin levels.
• Ferroportin Degradation: Hepcidin functions by binding to ferroportin, the only known cellular iron exporter found on macrophages and intestinal cells. This binding causes ferroportin to be internalized and degraded.
• Iron Sequestration: Without functional ferroportin on the cell surface, iron becomes trapped within macrophages (which recycle iron from old red blood cells) and hepatocytes. This effectively "locks" iron in storage, preventing it from entering the bloodstream and resulting in low serum iron despite high cellular stores.

Bottom line

The claim is fully supported by high-quality evidence. Inflammation increases hepcidin via the IL-6/STAT3 pathway, causing the degradation of ferroportin and sequestering iron within cells. This results in a diagnostic profile of low serum iron and TSAT (<20%) alongside normal or high ferritin levels.