Questions: Iron Metabolism, Bioavailability, and Deficiency States

Question 1

A vegetarian patient's diet is assessed to contain 18 mg of iron daily — meeting the recommended intake. Yet she is diagnosed with early-stage iron deficiency. What is the most likely explanation?

• A. 18 mg is insufficient for women regardless of dietary source
• B. She likely has an underlying gastrointestinal disorder blocking all iron absorption
• C. The majority of her dietary iron is non-heme, which has far lower bioavailability than heme iron — so effective absorbed iron is well below the apparent intake
• D. Iron deficiency in vegetarians is primarily caused by calcium from dairy products blocking absorption

Answer: (C)

This is the core paradox of iron nutrition: quantity on paper ≠ quantity absorbed. Non-heme iron (from plants and fortified foods) has 2–20% bioavailability vs. 15–35% for heme iron. A vegetarian diet may meet the RDA in raw milligrams while delivering a fraction of the absorbable iron a meat-eater would receive from the same number. This explains why vegetarians face higher deficiency risk even with apparently adequate dietary intake.

Question 2

A patient with severe rheumatoid arthritis has low hemoglobin but normal-to-elevated ferritin. Iron supplementation has little effect. Which mechanism best explains this presentation?

• A. Elevated hepcidin from chronic inflammation degrades ferroportin, trapping iron in storage depots and blocking its release into circulation
• B. The patient's enterocytes are inflamed and absorbing less dietary iron
• C. Rheumatoid arthritis causes occult blood loss that depletes storage iron faster than it accumulates
• D. Elevated transferrin saturation from inflammation blocks additional iron uptake by the erythroid marrow

Answer: (A)

This is anemia of chronic disease. Inflammation independently raises hepcidin, which binds and degrades ferroportin — the transporter that moves iron from enterocytes and macrophages into the bloodstream. Iron is present in stores (hence normal ferritin) but cannot be released to make hemoglobin. Oral iron supplementation fails because it can be absorbed into the enterocyte but not exported. This illustrates that hepcidin is the master regulator of iron availability, not just iron absorption.

Question 3

A falling hemoglobin level is the earliest reliable biochemical marker of iron deficiency.

• T. True
• F. False

Answer: False

Hemoglobin falls only in the third and final stage of iron deficiency — iron-deficiency anemia. By that point, the body has already exhausted storage iron (marked by falling ferritin) and gone through a phase of iron-deficient erythropoiesis (falling transferrin saturation, rising RDW). Serum ferritin is the earliest and most sensitive marker because it reflects storage depletion before any functional iron compartment is affected. Waiting for hemoglobin to fall misses the window for easy treatment.

Question 4

Consuming vitamin C alongside plant-based iron sources can substantially increase non-heme iron absorption.

• T. True
• F. False

Answer: True

Vitamin C (ascorbate) reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺) and chelates it in a soluble form that resists the inhibitory effects of phytates and polyphenols. Studies show up to sixfold enhancement of non-heme iron absorption when vitamin C is consumed in the same meal. This is clinically meaningful advice for vegetarians, pregnant women, and anyone at risk of deficiency — and illustrates how the dietary context surrounding iron matters as much as the iron content itself.

Question 5

Why does iron deficiency progress through distinct stages before anemia develops, and why does this staging matter clinically?

Model answer: The body maintains iron in separate compartments: storage iron (ferritin in liver, spleen, marrow), transport iron (transferrin-bound in blood), and functional iron (hemoglobin in red cells, enzymes). Deficiency depletes these compartments sequentially. Storage depletion comes first (ferritin falls), then transport iron drops (low transferrin saturation, rising RDW as new red cells are iron-poor), and only finally hemoglobin falls. This staging matters because ferritin-stage deficiency is easily corrected with supplementation, while full iron-deficiency anemia requires longer treatment, may signal chronic disease, and in vulnerable populations (children, pregnant women) has already caused measurable harm to cognition and fetal development.

The staging also explains why ferritin is the preferred screening test for at-risk populations. Treating stage 1 (depleted stores) prevents the downstream harms of stage 3. By contrast, if clinicians only check hemoglobin, they miss deficiency entirely until it is severe.